light-emitting element

Abstract

Light-emitting element comprising: a first electrode (103); a light-emitting layer (703) above the first electrode (103), wherein the light-emitting layer (703) comprises a guest material and a host material; and a second electrode (108) above the light-emitting layer (703), where a fluorescence spectrum of the host material and a phosphorescence spectrum of the host material overlap the absorption band on the longest wavelength side (the side of lowest energy) in the absorption spectrum of the guest material, wherein the difference between the energy value of the maximum of the fluorescence spectrum of the host material and the energy value of the maximum of the absorption band on the side of the lowest energy in the absorption spectrum of the guest material, wherein this maximum has an absorption wavelength corresponding to a direct transition from the singlet ground state to the lowest excited triplet state of the guest material, is 0.2 eV or less, wherein the host material is a mixture of a heterocyclic compound and an aromatic amine compound or carbazole compound, and where the level of a triplet excitation energy of the host material is higher than the level of a triplet excitation energy of the guest material.

Description

Technical field

[0001] The present invention relates to light-emitting elements that utilize a phenomenon of organic electroluminescence (EL) (hereinafter such light-emitting elements are also referred to as organic EL elements). Background of the technology

[0002] An organic EL element has been actively researched and developed. In a basic structure, an organic EL element consists of a layer containing a luminescent organic compound (hereinafter also referred to as the light-emitting layer) positioned between a pair of electrodes. Due to properties such as the ability to be thinner and lighter, a high-speed response to input signals, and the capacity to operate at low voltage with direct current, the organic EL element has attracted attention as a next-generation flat panel display element. Furthermore, a feature of a display using such a light-emitting element is its excellent contrast and image quality, as well as its wide viewing angle.Since it is a planar light source, attempts have also been made to use the organic EL element as a light source, for example as backlighting for a liquid crystal display and for a lighting device.

[0003] The emission mechanism of the organic light-emitting cell (EL cell) is a type of charge carrier injection. That is, by applying a voltage, with a light-emitting layer positioned between electrodes, electrons and holes injected by the electrodes recombine, exciting a light-emitting substance. Light is emitted when the substance relaxes from the excited state to the ground state. Two types of excited states are possible: an excited singlet state (S*) and an excited triplet state (T*). The statistical generation ratio of excited states in a light-emitting cell is assumed to be S*:T* = 1:3.

[0004] In general, the ground state of a light-emitting organic compound is a singlet state. Therefore, light emission from the excited singlet state (S*) is called fluorescence, as it is caused by an electron transfer between the same spin multiplicities. In contrast, light emission from the excited triplet state (T*) is called phosphorescence, where an electron transfer occurs between different spin multiplicities. In general, for a compound that emits fluorescence (hereinafter referred to as a fluorescent compound), phosphorescence is not observed at room temperature; only fluorescence is observed.Accordingly, it is assumed that the internal quantum efficiency (the ratio of generated photons to injected charge carriers) in a light-emitting element containing a fluorescent compound has a theoretical limit of 25% based on S*:T* = 1:3.

[0005] In contrast, when using a phosphorescent-emitting compound (hereinafter referred to as the phosphorescent compound), an internal quantum efficiency of 100% can theoretically be achieved. That is, a higher emission efficiency can be achieved than when using a fluorescent compound. For these reasons, a light-emitting element incorporating a phosphorescent compound has been actively developed in recent years to achieve a highly efficient light-emitting element. As a phosphorescent compound, a metal-organic complex featuring iridium or the like as the central metal has attracted particular attention due to its high phosphorescence quantum yield; for example, a metal-organic complex featuring iridium as the central metal is disclosed as a phosphorescent material in Patent 1 and in Publications 1 to 5.

[0006] When a light-emitting layer of a light-emitting element is formed using a phosphorescent compound as described above, in order to suppress concentration quenching or quenching due to triplet-triplet annihilation in the phosphorescent compound, the light-emitting layer is often designed such that the phosphorescent compound is dispersed in a matrix of another compound. Here, the compound serving as the matrix is ​​referred to as the host material, and the compound dispersed in the matrix, such as a phosphorescent compound, is referred to as the guest material. [Reference][Patent Specification]

[0007] [Patent 1] International Disclosure of Printed Matter WO 00 / 70 655 A2 [Veröffentlichung 1] M. E. Kondakova et al. „High-efficiency, low-voltage phosphorescent organic light emitting diode devices with mixed host“, Journal of Applied Physics 104, 094501, 2008. [Veröffentlichung 2] X. Gong et al. „Phosphorescence from iridium complexes doped into polymer blends“, J. Appl. Phys. 95, 2004. [Veröffentlichung 3]: Y. Hino et al. „Red Phosphorescent Organic Light-Emitting Diodes Using Mixture System of Small-Molecule and Polymer Host“, Jpn. J. Appl. Phys., 44, 2790, 2005. [Veröffentlichung 4] Xia, Hong et al. „Efficient electrophosphorescence from lowcost copper (I) complex“, Optical Materials, Vol. 29, 2007, No. 6, S. 667-671. [Veröffentlichung 5] A. B. Tamayo et al. „Synthesis and Characterization of Facial and Meridional Triscyclometalated Iridium(111) Complexes“, JACS, 2003. Offenlegung der Erfindung

[0008] In general, the light extraction efficiency of an organic EL element is approximately 20% to 30%. Taking into account the light absorption by a reflective electrode and a transparent electrode, the external quantum efficiency of a light-emitting element containing a phosphorescent compound is therefore limited to a maximum of approximately 25%.

[0009] One objective of an embodiment of the present invention is to provide a light-emitting element with high external quantum efficiency. Another objective of an embodiment of the present invention is to provide a light-emitting element with a long lifetime.

[0010] The invention relates to a light-emitting element according to one of the independent claims, as well as an electronic device according to claim 10 and a lighting device according to claim 11. Advantageous embodiments are specified in the dependent claims. In one embodiment of the present invention, the light-emitting element comprises a light-emitting layer between a pair of electrodes, the layer comprising a guest material and a host material, wherein an emission spectrum of the host material overlaps an absorption spectrum of the guest material, and phosphorescence is emitted by converting an excitation energy of the host material into an excitation energy of the guest material.

[0011] In a further embodiment of the present invention, a light-emitting element comprises a light-emitting layer between a pair of electrodes, which includes a guest material and a host material, wherein an emission spectrum of the host material overlaps an absorption band on the longest wavelength side (the side of lowest energy) in an absorption spectrum of the guest material, and phosphorescence is emitted by converting an excitation energy of the host material into an excitation energy of the guest material.

[0012] In the above light-emitting element, the absorption band on the longest wavelength side preferably includes absorption based on a triplet MLCT (metal to ligand charge transfer) transition.

[0013] The emission spectrum of the host material of the above light-emitting element is preferably a fluorescence spectrum.

[0014] In the above light-emitting element, the guest material is preferably a metal-organic complex, more preferably an iridium complex.

[0015] For the above light-emitting element, the difference between the energy value of a maximum of the emission spectrum and the energy value of a maximum of the absorption band on the side of the lowest energy in the absorption spectrum is preferably 0.3 eV or less.

[0016] For the light-emitting element above, the molar absorption coefficient of the absorption band at the longest wavelength side in the absorption spectrum is preferably 5,000 M. -1 ·cm -1 or more.

[0017] According to one embodiment of the present invention, a light-emitting element with high external quantum efficiency can be provided. According to another embodiment of the present invention, a light-emitting element with a long lifetime can be provided. Brief description of the drawings

[0018] The following applies to the attached drawings: Fig. 1A and Fig. 1B represents absorption spectra and emission spectra according to Example 1; Fig. Figure 2 illustrates the structure of light-emitting elements by examples; Fig. Figure 3 represents a current density-luminance characteristic curve of light-emitting elements from Example 2; Fig. Figure 4 represents a voltage-luminance characteristic curve of the light-emitting elements of Example 2; Fig.Figure 5 represents a luminance-current efficiency characteristic of the light-emitting elements of Example 2; Fig. Figure 6 represents a characteristic curve of the luminance against the external quantum efficiency of the light-emitting elements of Example 2; Fig. Figure 7 represents the emission spectra of the light-emitting elements from Example 2; Fig. Figure 8 presents the results of reliability tests of the light-emitting elements of Example 2; Fig. Figure 9 represents a current density-luminance characteristic curve of a light-emitting element from Example 3; Fig. Figure 10 represents a voltage-luminance characteristic curve of the light-emitting element of Example 3; Fig. Figure 11 represents a luminance-current efficiency characteristic of the light-emitting element of Example 3; Fig.Figure 12 represents a characteristic curve of the luminance versus the external quantum efficiency of the light-emitting element of Example 3; Fig. Figure 13 represents an emission spectrum of the light-emitting element from Example 3; Fig. 14 presents results of reliability tests of the light-emitting element of Example 3; Fig. Figures 15A to 15C illustrate light-emitting elements of embodiments of the present invention; Fig. Figure 16 presents absorption spectra and an emission spectrum according to Example 1; Fig. 17A and Fig. 17B presents absorption spectra and emission spectra according to Example 4; Fig. Figure 18 represents a current density-luminance characteristic curve of a light-emitting element from Example 5; Fig. Figure 19 represents a voltage-luminance characteristic curve of the light-emitting element of Example 5; Fig. Figure 20 represents a luminance-current efficiency characteristic of the light-emitting element of Example 5; Fig. Figure 21 represents a characteristic curve of the luminance versus the external quantum efficiency of the light-emitting element of Example 5; Fig. Figure 22 represents an emission spectrum of the light-emitting element of Example 5; Fig. 23A and Fig. 23B represent absorption spectra and emission spectra according to Example 6; Fig. Figure 24 represents a current density-luminance characteristic curve of a light-emitting element from Example 7; Fig. Figure 25 represents a voltage-luminance characteristic curve of the light-emitting element of Example 7; Fig. Figure 26 represents a luminance-current efficiency characteristic of the light-emitting element of Example 7; Fig.Figure 27 represents a characteristic curve of the luminance versus the external quantum efficiency of the light-emitting element of Example 7; Fig. Figure 28 represents an emission spectrum of the light-emitting element of Example 7; Fig. 29 presents results of reliability tests of the light-emitting element of Example 7; Fig. 30A and Fig. 30B represent absorption spectra and emission spectra according to Example 8; Fig. Figure 31 represents a current density-luminance characteristic curve of light-emitting elements from Example 9; Fig. Figure 32 represents a voltage-luminance characteristic curve of the light-emitting elements of Example 9; Fig. Figure 33 represents a luminance-current efficiency characteristic of the light-emitting elements of Example 9; Fig.Figure 34 represents a characteristic curve of the luminance against the external quantum efficiency of the light-emitting elements of Example 9; Fig. Figure 35 presents emission spectra of the light-emitting elements of Example 9; Fig. 36 presents results of reliability tests of the light-emitting elements of Example 9; Fig. 37A and Fig. 37B presents absorption spectra and emission spectra according to Example 10; Fig. Figure 38 represents a current density-luminance characteristic curve of light-emitting elements from Example 11; Fig. Figure 39 represents a voltage-luminance characteristic curve of the light-emitting elements of Example 11; Fig. Figure 40 represents a luminance-current efficiency characteristic of the light-emitting elements of Example 11; Fig.Figure 41 represents a characteristic curve of the luminance versus the external quantum efficiency of the light-emitting elements of Example 11; Fig. 42 represents emission spectra of the light-emitting elements of Example 11; Fig. 43A and Fig. 43B presents absorption spectra and emission spectra according to Example 12; Fig. Figure 44 represents a current density-luminance characteristic curve of light-emitting elements from Example 13; Fig. Figure 45 represents a voltage-luminance characteristic curve of the light-emitting elements of Example 13; Fig. Figure 46 represents a luminance-current efficiency characteristic of the light-emitting elements of Example 13; Fig. Figure 47 represents a characteristic curve of the luminance against the external quantum efficiency of the light-emitting elements of Example 13; Fig.48 represents emission spectra of the light-emitting elements of Example 13; Fig. 49A and Fig. 49B presents absorption spectra and emission spectra according to Example 14; Fig. Figure 50 represents a current density-luminance characteristic curve of light-emitting elements from Example 15; Fig. Figure 51 represents a voltage-luminance characteristic curve of the light-emitting elements of Example 15; Fig. Figure 52 represents a luminance-current efficiency characteristic of the light-emitting elements of Example 15; Fig. Figure 53 represents a characteristic curve of the luminance versus the external quantum efficiency of the light-emitting elements of Example 15; and Fig. Figure 54 presents emission spectra of the light-emitting elements of Example 15. The best method for carrying out the invention

[0019] Embodiments are described with reference to the drawings. It should be noted that the invention is not limited to the following description, and it is readily apparent to those familiar with the technology that various changes and modifications can be made without departing from the concept and scope of the invention. Therefore, the invention should not be understood as being limited to the description in the following embodiments. It should be noted that in the structures of the invention described below, the same sections, or sections having similar functions, are designated by the same reference numerals in different drawings, and the description of such sections is not repeated. (Version 1)

[0020] Embodiment 1 represents a light-emitting element of an embodiment of the present invention.

[0021] The light-emitting element of this embodiment comprises a light-emitting layer containing a guest material as the light-emitting substance and a host material in which the guest material is dispersed. A phosphorescent compound is used as the guest material. One or more types of organic compounds can be used as the host material.

[0022] The structure in which the guest material is dispersed within the host material can prevent the light-emitting layer from crystallizing. Furthermore, concentration quenching due to a high concentration of the guest material can be suppressed, and consequently, the light-emitting element can exhibit a higher emission efficiency.

[0023] According to this embodiment, it is desirable that the level of the triplet excitation energy (T1 level) of the organic compound used as the host material be higher than that of the guest material. The reason for this is that if the T1 level of the host material is lower than that of the guest material, the triplet excitation energy of the guest material, which is intended to contribute to light emission, is canceled out by the host material, and consequently the emission efficiency is reduced. (Elementary processes of light emission)

[0024] First, general elementary processes of light emission in a light-emitting element using a phosphorescent compound as a guest material are described.

[0025] (1) The case in which an electron and a hole in a guest molecule are recombined and the guest molecule is excited (direct recombination process).

[0026] (1-1) If the excited state of the guest molecule is an excited triplet state, the guest molecule emits phosphorescence.

[0027] (1-2) If the excited state of the guest molecule is an excited singlet state, the guest molecule in the excited singlet state undergoes intersystem crossing to an excited triplet state and emits phosphorescence.

[0028] In other words, the direct recombination process in (1) can achieve high emission efficiency, provided the intersystem crossing efficiency and the phosphorescence quantum yield of the guest molecule are high. As described above, it is desirable for the T1 level of the host molecule to be higher than that of the guest molecule.

[0029] (2) The case in which an electron and a hole in a host molecule are recombined and the host molecule is brought into an excited state (energy transfer process).

[0030] (2-1) If the excited state of the host molecule is an excited triplet state and the T1 level of the host molecule is higher than that of the guest molecule, excitation energy is transferred from the host molecule to the guest molecule, and the guest molecule is consequently excited to a triplet state. The guest molecule in the excited triplet state emits phosphorescence. It should be noted that, theoretically, energy can be transferred to a singlet excitation energy level (S1 level) of the guest molecule; however, since the S1 level of the guest molecule has a higher energy than the T1 level of the host molecule in many cases, it is unlikely that energy transfer to the S1 level of the guest molecule is a major energy transfer process; therefore, this is not described here.

[0031] (2-2) If the excited state of the host molecule is an excited singlet state and the S1 level of the host molecule is higher than the S1 level and the T1 level of the guest molecule, excitation energy is transferred from the host molecule to the guest molecule, and the guest molecule is consequently excited to an excited singlet state or an excited triplet state. The guest molecule in the excited triplet state emits phosphorescence. Furthermore, the guest molecule in the excited singlet state undergoes intersystem crossing to an excited triplet state and emits phosphorescence.

[0032] In other words, in the energy transfer process in (2) it is important how efficiently both the triplet excitation energy and the singlet excitation energy of the host molecule can be transferred to the guest molecule. (Energy transfer process)

[0033] The following section describes in detail the energy transfer processes between molecules.

[0034] Initially, the following two mechanisms are proposed as mechanisms for energy transfer between molecules. A molecule that releases excitation energy is called a host molecule, whereas a molecule that absorbs the excitation energy is called a guest molecule. (Förster mechanism (dipole-dipole interaction))

[0035] In the Förster mechanism (also known as Förster resonance energy transfer), no direct intermolecular contact is required for energy transfer. Energy transfer occurs through a resonance phenomenon of a dipole vibration between a host molecule and a guest molecule. This resonance phenomenon causes the host molecule to transfer energy to the guest molecule; consequently, the host molecule relaxes to a ground state, and the guest molecule is excited. The rate constant k h*→g The Förster mechanism is expressed by a formula (1). [Formula 1)] kh*→g=9000c4K2ϕln10128π5n4NτR6∫f'h(ν)εg(ν)ν4dν

[0036] In formula (1) v represents a frequency, f' h(v) represents a normalized emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from an excited singlet state and a phosphorescence spectrum for energy transfer from an excited triplet state), ε g (v) denotes a molar absorption coefficient of a guest molecule, N denotes Avogadro's number, n denotes a refractive index of a medium, R denotes an intermolecular distance between the host molecule and the guest molecule, τ denotes a measured lifetime of an excited state (a fluorescence lifetime or phosphorescence lifetime), c denotes the speed of light, ϕ denotes 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 2denotes a coefficient (0 to 4) of the orientation of a transition dipole moment between the host molecule and the guest molecule. It should be noted that with arbitrary orientation K 2 = 2 / 3 applies. (Dexter mechanism (electron exchange interaction))

[0037] In the Dexter mechanism (also known as Dexter electron transfer), a host molecule and a guest molecule are located close to a contact-effective region where their orbitals overlap. The host molecule, in an excited state, and the guest molecule, in a ground state, exchange electrons, resulting in energy transfer. The rate constant k h*→g The Dexter mechanism is expressed by a formula (2). [Formula (2)] kh*→g=(2πh)K2exp(−2RL)∫f'h(ν)ε'g(ν)dν

[0038] In formula (2), h represents a Planck constant, K represents a constant that has an energy dimension, v represents a frequency, f' h (v) represents a normalized emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from an excited singlet state and a phosphorescence spectrum for energy transfer from an excited triplet state), ε' g (v) represents a normalized absorption spectrum of a guest molecule, L represents an effective molecular radius, and R represents an intermolecular distance between the host molecule and the guest molecule.

[0039] Here, it is assumed that the efficiency of energy transfer from the host molecule to the guest molecule (energy transfer efficiency Φ) ET ) is expressed by a formula (3). In the formula, k means ra rate constant of a light emission process (fluorescence in the case of energy transfer from an excited singlet state and phosphorescence in the case of energy transfer from an excited triplet state) of the host molecule, k n represents a rate constant of a non-light emission process (thermal deactivation or intersystem crossing) of the host molecule, and τ represents a measured lifetime of the excited state of the host molecule. [Formula (3)] ΦET=kh*→gkr+kn+kh*→g=kh*→g(1τ)+kh*→g

[0040] According to formula (3), to determine the energy transmission efficiency Φ ET to increase the velocity constant k h*→g the energy transfer, initially in comparison with another competing rate constant k r + k n (= 1 / τ) can be increased further. To determine the velocity constant k h*→gTo increase the energy transfer, an emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from an excited singlet state largely overlaps a phosphorescence spectrum for energy transfer from an excited triplet state) and an absorption spectrum of a guest molecule are then preferably obtained on the basis of formulas (1) and (2) for the Förster mechanism and the Dexter mechanism.

[0041] In one embodiment of the present invention, a light-emitting element is included which comprises a light-emitting layer between a pair of electrodes, the layer comprising a guest material and a host material, wherein an emission spectrum of the host material overlaps an absorption spectrum of the guest material and phosphorescence is emitted by converting an excitation energy of the host material into an excitation energy of the guest material.

[0042] According to one embodiment of the present invention, energy is transferred smoothly from the host material to the guest material by means of the overlap of the emission spectrum of the host material and the absorption spectrum of the guest material, resulting in high energy transfer efficiency. In this way, according to one embodiment of the present invention, a light-emitting element with high external quantum efficiency can be achieved.

[0043] In view of the energy transfer processes described above, if the host molecule's excitation energy is deactivated by emitting the excitation energy as light or heat before it is transferred to the guest molecule, the emission efficiency is reduced and the lifetime is shortened. However, according to one embodiment of the present invention, the energy is transferred smoothly, thus suppressing the deactivation of the excitation energy. In this way, a light-emitting element with a long lifetime can be achieved.

[0044] Here, the inventors of this invention have taken into account that the absorption band on the longest wavelength side (the side of lowest energy) in the absorption spectrum of the guest molecule is important when considering the overlap of the emission spectrum of the host molecule and the absorption spectrum of the guest molecule.

[0045] According to this embodiment, a phosphorescent compound is used as the guest material. In the absorption spectrum of the phosphorescent compound, an absorption band that is thought to contribute most to light emission is an absorption wavelength corresponding to a direct transition from an excited singlet state to an excited triplet state and a proximity of the absorption wavelength to the longest wavelength side. Therefore, it is considered desirable for the emission spectrum (a fluorescence spectrum and a phosphorescence spectrum) of the host material to overlap with the absorption band at the longest wavelength side in the absorption spectrum of the phosphorescent compound.

[0046] For example, most organometallic complexes, especially light-emitting iridium complexes, exhibit a broad absorption band from about 500 nm to 600 nm along the longest wavelength side (in fact, the broad absorption band may be located along a shorter or longer wavelength side depending on the emission wavelengths). This absorption band is primarily based on a triplet MLCT (metal-ligand charge transfer) transition. It should be noted that the absorption band also includes absorptions based on a triplet π-π* transition and a singlet MLCT transition, and that these absorptions overlap, thus forming a broad absorption band along the longest wavelength side of the absorption spectrum.Therefore, as described above, it is desirable that the broad absorption band on the longest wavelength side largely overlaps the emission spectrum of the host material when a metal-organic complex (especially an iridium complex) is used as the guest material.

[0047] Accordingly, a further embodiment of the present invention comprises a light-emitting element comprising a light-emitting layer between a pair of electrodes, which includes a guest material and a host material, wherein an emission spectrum of the host material overlaps an absorption band on the longest wavelength side in an absorption spectrum of the guest material, and phosphorescence is emitted by converting an excitation energy of the host material into an excitation energy of the guest material.

[0048] In the light-emitting element described above, the absorption band preferentially includes absorption based on the triplet MLCT transition. An excited triplet MLCT state is the lowest excited triplet state of the phosphorescent compound, which is the guest material, and consequently, the phosphorescent compound emits phosphorescence from this state. That is, phosphorescence from the excited triplet MLCT state is associated with few other deactivation processes besides light emission, and therefore, high emission efficiency is expected to be achieved by maximizing the presence rate of this excited state.For these reasons, numerous energy transfer processes are preferably present in which energies are transferred directly from the host material to the excited triplet MLCT state via absorption based on the triplet MLCT transition. In the light-emitting element described above, the guest material is preferably a metal-organic complex, more preferably an iridium complex.

[0049] The inventors have determined that when the host molecule is in an excited singlet state (the one above (2-2)), it is unlikely that energy will be transferred to the guest molecule, i.e., the phosphorescent compound, and that the emission efficiency is likely to be reduced compared to when the host molecule is in an excited triplet state (the one above (2-1)). Consequently, the inventors have focused on this fact as their objective.

[0050] A fluorescent compound is generally used as the host material, but its fluorescence lifetime (τ) is extremely short and is in the nanosecond range (k). r +k n is high). The reason for this is that a transition from the excited singlet state to the ground state (singlet) is a permissible transition. From formula (3) it follows that this is unfavorable for the energy transfer efficiency Φ. ET Considering this, it is generally unlikely that energy will be transferred from the host material to the guest material in an excited singlet state.

[0051] However, one embodiment of the present invention can solve such a problem of the efficiency of energy transfer from the host material in the excited singlet state to the guest material. That is, according to one embodiment of the present invention, a light-emitting element between a pair of electrodes includes a light-emitting layer containing a guest material and a host material. A fluorescence spectrum of the host material preferably overlaps an absorption band at the longest wavelength side in an absorption spectrum of the guest material, and by means of this overlap, phosphorescence is emitted by converting an excitation energy of the host material into an excitation energy of the guest material.

[0052] That is, in a light-emitting element according to one embodiment of the present invention, the fluorescence spectrum of the host material overlaps the absorption band at the longest wavelength side in the absorption spectrum of the guest material, and phosphorescence is emitted by means of this overlap through the conversion of an excitation energy of the host material into an excitation energy of the guest material. Such a structure can suppress the deactivation of the singlet excitation energy. Accordingly, an application of one embodiment of the present invention can suppress the deactivation of the singlet excitation energy of the host material, which can impair not only the efficiency of an element but also its lifetime, thus enabling the creation of a light-emitting element with a long lifetime.Here, it is desirable that sufficient excitation energy from the host material is transferred to the phosphorescent compound and that essentially no fluorescence from the excited singlet state is observed.

[0053] To ensure that the emission spectrum of the host material sufficiently overlaps with the absorption spectrum of the guest material, the difference between the energy value of a maximum in the emission spectrum and the energy value of a maximum in the absorption band on the side of lowest energy in the absorption spectrum is preferably 0.3 eV or less. More preferably, the difference is 0.2 eV or less, and even more preferably 0.1 eV or less.

[0054] Furthermore, the Förster mechanism is considered important for energy transfer from the host material in the excited singlet state. Taking this into account, equation (1) shows that the molar absorption coefficient of the absorption band at the longest wavelength side of the host material is preferably 2000 M. -1 ·cm -1 or higher, preferably 5,000 m -1 ·cm -1 or higher.

[0055] It should be noted that this embodiment can optionally be combined with the other embodiment. (Version 2)

[0056] This embodiment represents a light-emitting element of an embodiment of the present invention with reference to Fig. 15A to 15C.

[0057] Fig.Figure 15A illustrates a light-emitting element that includes an EL layer 102 between a first electrode 103 and a second electrode 108. The light-emitting element in Fig. 15A includes a hole injection layer 701, a hole transport layer 702, a light-emitting layer 703, an electron transport layer 704 and an electron injection layer 705, which are stacked in this order over the first electrode 103, and the second electrode 108 which is provided above it.

[0058] The first electrode 103 is preferably formed using any metals, alloys, conductive compounds, mixtures thereof, and the like, which have a high work function (particularly 4.0 eV or higher). Specific examples include indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxide containing tungsten oxide and zinc oxide (IWZO), and the like. Films of these conductive metal oxides are usually formed by a sputtering process, but can also be formed by a sol-gel process or the like. For example, an indium oxide-zinc oxide film can be formed by a sputtering process using a target in which zinc oxide is added to indium oxide at a rate of 1 wt.% to 20 wt.%.Furthermore, an IWZO film can be formed by a sputtering process using a target in which tungsten oxide is added to indium oxide at a rate of 0.5 wt.% to 5 wt.%, and zinc oxide is added to indium oxide at a rate of 0.1 wt.% to 1 wt.%. Other examples include graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, nitrides of metallic materials (e.g., titanium nitride), and the like.

[0059] It should be noted that if a layer contained in the EL layer 102 and formed in contact with the first electrode 103 is formed using a composite material described later, which is formed by combining an organic compound and an electron acceptor, the first electrode 103 can be formed using any variety of metals, alloys, electrically conductive compounds, mixtures thereof, and the like, regardless of the work function; for example, aluminum, silver, an aluminum-containing alloy (e.g., Al-Si), or the like can also be used.

[0060] The first electrode 103 can be formed, for example, by a sputtering process, a vapor deposition process (such as a vacuum vapor deposition process) or the like.

[0061] The second electrode 108 is preferably formed using any metals, alloys, electrically conductive compounds, mixtures thereof, and the like, which have a low work function (in particular, 3.8 eV or less). Certain examples include elements belonging to groups 1 and 2 of the periodic table, that is, alkali metals such as lithium and cesium, alkaline earth metals such as calcium and strontium, magnesium, alloys thereof (e.g., Mg-Ag and Al-Li), rare earth metals such as europium and ytterbium, alloys thereof, aluminum, silver, and the like.

[0062] If a layer contained in the EL layer 102 and formed in contact with the second electrode 108 is formed using a composite material described later, which is formed by combining an organic compound and an electron donor (a donor), the second electrode 108 can be formed independently of the work function using any variety of conductive materials such as Al, Ag, ITO and indium oxide-tin oxide containing silicon or silicon oxide.

[0063] It should be noted that when forming the second electrode 108, a vacuum evaporation process or a sputtering process can be used. If a silver paste or the like is used, a coating process, an inkjet process, or the like can be employed.

[0064] The EL layer 102 includes at least the light-emitting layer 703. A known substance can be used for part of the EL layer 102, and it can be either a low-molecular-weight or a high-molecular-weight compound. It should be noted that the substances forming the EL layer 102 can consist of organic compounds or may contain an organic compound as a component.

[0065] As in Fig.As illustrated in Figure 15A, the EL layer 102 further includes not only the light-emitting layer 703, but also the following layers in a suitable combination: the hole injection layer 701, which contains a substance with a high hole injection capacity, the hole transport layer 702, which contains a substance with a high hole transport capacity, the electron transport layer 704, which contains a substance with a high electron transport capacity, the electron injection layer 705, which contains a substance with a high electron injection capacity, and the like.

[0066] The 701 hole injection layer is a layer containing a substance with high hole injection capability. Examples of substances with high hole injection capability include metal oxides such as molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungsten oxide, and manganese oxide. Alternatively, a phthalocyanine-based compound such as phthalocyanine (abbreviation: H₂Pc) or copper(II) phthalocyanine (abbreviation: CuPc) can be used.

[0067] Other examples include aromatic amine compounds and the like, which are low-molecular-weight organic compounds, such as 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-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B), 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) and 3-[N-(1-Naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1).

[0068] Other examples include high-molecular-weight compounds (e.g., oligomers, dendrimers, and polymers) such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino)phenyl)methacrylamide] (abbreviation: PTPDMA) and poly[N,N'bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: poly-TPD), and high-molecular-weight compounds to which an acid is added, such as poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS) and polyaniline / poly(styrenesulfonic acid) (PAni / PSS).

[0069] The hole injection layer 701 can be formed using the composite material created by combining an organic compound and an electron acceptor. Such a composite material exhibits high hole injection and hole transport capabilities because the electron acceptor generates holes in the organic compound. In this case, the organic compound is preferably a material that excellently transports the generated holes (a substance exhibiting high hole transport capability).

[0070] Examples of the organic compound used for the composite material can include a variety of compounds such as aromatic amines, carbazole derivatives, aromatic hydrocarbons, and high-molecular-weight compounds (e.g., oligomers, dendrimers, and polymers). The organic compound used for the composite material is preferably an organic compound with a high hole transport capacity, and in particular, preferably a substance exhibiting a hole mobility of 10 -6 cm 2 exhibits / V·s or higher. It should be noted that, apart from these substances, any substance capable of transporting more holes than electrons can be used. Organic compounds that can be used for the composite material are described in detail below.

[0071] Examples of organic compounds that can be used for the composite material include aromatic amine compounds such as TDATA, MTDATA, DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD) and 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and carbazole derivatives such as 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(N-carbazolyl)phenyl]-10-phenylanthracene (abbreviation: CzPA), 9-Phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PCzPA) and 1,4-Bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

[0072] Other examples include aromatic hydrocarbon compounds such as 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), 9,10-Bis[2-(1-naphthyl)phenyl]-2-tert-butylanthracene, 9,10-Bis[2-(1-naphthyl)phenyl]anthracene and 2,3,6,7-Tetramethyl-9,10-di(1-naphthyl)anthracene.

[0073] Further examples include aromatic hydrocarbon compounds such as 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, pentacene, coronene, 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (Abbreviation: DPVPA).

[0074] Furthermore, examples of electron acceptors include organic compounds such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ) and chloranil, oxides of transition metals, oxides of metals belonging to groups 4 to 8 of the periodic table, and the like. Vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are particularly favored due to their high electron acceptance capacity. Of these, molybdenum oxide is especially preferred because it is air-stable, has low hygroscopic properties, and is easy to handle.

[0075] The composite material can be formed using the electron acceptor and high molecular weight compound described above, such as PVK, PVTPA, PTPDMA or Poly-TPD, and can be used for the hole injection layer 701.

[0076] The hole transport layer 702 is a layer containing a substance with a high hole transport capacity. Examples of substances with high hole transport capacity include aromatic amine compounds such as NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), and 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB). The substances mentioned here primarily exhibit a hole mobility of 10 -6 cm 2exhibiting / V·s or higher. It should be noted that, apart from these substances, any substance capable of transporting more holes than electrons can be used. It should also be noted that the layer containing a substance with a high hole transport capacity is not limited to a single layer and can consist of a stack of two or more layers containing any of the above substances.

[0077] Alternatively, the hole transport layer 702 can be formed using a carbazole derivative such as CBP, CzPA or PCzPA or an anthracene derivative such as t-BuDNA, DNA or DPAnth.

[0078] Furthermore, the hole transport layer 702 can alternatively be formed using a high molecular weight compound such as PVK, PVTPA, PTPDMA or Poly-TPD.

[0079] The light-emitting layer 703 is a layer containing a light-emitting substance. The light-emitting layer 703 of this embodiment comprises a guest material and a host material. Several types of materials can be used as host materials. Details can be found in embodiment 1.

[0080] A metal-organic complex is preferred as the phosphorescent compound, and in particular an iridium complex. Taking into account energy transfer due to the Förster mechanism described above, the molar absorption coefficient of the absorption band at the longest wavelength side of the phosphorescent compound is preferably 2000 M. -1 ·cm -1 or higher, preferably 5,000 m -1 ·cm -1or higher. Certain examples of compounds exhibiting such a high molar absorption coefficient include bis(3,5-dimethyl-2-phenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), and (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [lr(m PPM )2(acac)]), (Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]) and the like. In particular, a material having a molar absorption coefficient of 5,000 M -1 ·cm -1 or higher, such as [Ir(dppm)2(acac)], provide a highly efficient light-emitting element with an external quantum efficiency of about 30%.

[0081] A preferred host material is a mixture of a compound likely to accept electrons (usually a heterocycle) and a compound likely to accept holes (usually an aromatic amine or a carbazole compound). With such a structure, a light-emitting layer can exhibit an excellent charge carrier balance between hole and electron transport, thereby increasing emission efficiency and lifetime.Specific examples of the host material include a mixture of 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) and 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), a composite of 2mDBTPDBq-II and 4,4'-Di(1-naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), a composite of 2-[4-(3,6-Diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III) and PCBNBB, a composite of 2-[4-(Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: DBTBIm-II) and 4,4',4''-Tris[N-(1-naphthyl)-N-phenylamino]-triphenylamine (abbreviation: 1'-TNATA) and the like.Alternatively, a mixture of 2mDBTPDBq-II and any of the following can be used as the host material: 4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), 4-(1-naphthyl)-4'-phenyltriphenylamine (abbreviation: αNBA1BP), 2,7-Bis[N-(diphenylaminophenyl)-N-phenylamino]-spiro-9,9'-bifluorene (abbreviation: DPA2SF), 9-Phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP), and 1'-TNATA. It should be noted that any other known host material can also be used without restriction to the substances listed above.

[0082] Furthermore, by providing multiple layers and designing their emission colors differently, light emission of a desired color can be achieved from the light-emitting element as a whole. For example, the emission colors of the first and second light-emitting layers in a light-emitting element with both light-emitting layers are complementary, so that the light-emitting element as a whole can emit white light. It should be noted that the word "complementary" means a color relationship in which an achromatic color is obtained when colors are mixed. That is, white light emission can be achieved by mixing light from substances whose emission colors are complementary. This can be applied to a light-emitting element with three or more light-emitting layers.

[0083] Electron transport layer 704 is a layer containing a substance with a high electron transport capacity. Examples of substances with high electron transport capacity include metal complexes such as Alq3, Tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3), Bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq2), BAlq, Zn(BOX)2, and Bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)2). Other examples include heteroaromatic compounds 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-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), and 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (Abbreviation: BzOs).Further examples include high-molecular-weight compounds such as poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), and poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy). The substances mentioned here are mainly those with an electron mobility of 10. -6 cm 2 / V·s or higher. It should be noted that, apart from these substances, any substance capable of transporting more holes than electrons can be used for the electron transport layer.

[0084] Furthermore, the electron transport layer is not limited to a single layer and can be a stack of two or more layers containing any of the above substances.

[0085] The electron injection layer 705 is a layer containing a substance with a high electron injection capability. Examples of substances that can be used for the electron injection layer 705 include alkali metals, alkaline earth metals and compounds thereof, such as lithium, cesium, calcium, lithium fluoride, cesium fluoride, calcium fluoride, and lithium oxide; rare earth metal compounds, such as erbium fluoride; and the substances mentioned above that are used for the electron transport layer 704.

[0086] Alternatively, a composite material formed by combining an organic compound and an electron donor can be used for the electron injection layer 705. Such a composite material exhibits high electron injection and electron transport capabilities because electrons are generated in the organic compound by the electron donor. The organic compound is preferably a material that transports the generated electrons excellently, and in particular, any of the substances mentioned above (such as metal complexes and heteroaromatic compounds) can be used for the electron transport layer 704. The electron donor can be a substance that exhibits the ability to donate electrons to the organic compound.Preferred examples of electron donors include alkali metals, alkaline earth metals, and rare earth metals such as lithium, cesium, magnesium, calcium, erbium, and ytterbium, as well as alkali metal oxides and alkaline earth metal oxides such as lithium oxide, calcium oxide, and barium oxide. Furthermore, a Lewis base such as magnesium oxide or an organic compound such as tetrathiafulvalene (abbreviation: TTF) can be used.

[0087] It should be noted that each of the above-mentioned hole injection layer 701, hole transport layer 702, light emitting layer 703, electron transport layer 704 and electron injection layer 705 can be formed by a process such as a vapor deposition process (e.g. a vacuum vapor deposition process), an inkjet process or a coating process.

[0088] A large number of EL layers can be stacked between the first electrode 103 and the second electrode 108, as shown in Fig.Figure 15B illustrates this. In this case, a charge-generating layer 803 is preferably provided between a first EL layer 800 and a second EL layer 801, which are stacked. The charge-generating layer 803 can be formed using the composite material described above. Furthermore, the charge-generating layer 803 can have a stacked structure consisting of a layer containing the composite material and a layer containing another material. In this case, the layer containing another material can be a layer containing an electron-donating substance and a substance with a high electron transport capacity, a layer formed from a transparent conductive film, or the like.Regarding a light-emitting element (EL) with such a structure, energy transfer and quenching problems are minimal, and due to a wider selection of materials, it is easy to create an EL with both high emission efficiency and a long lifetime. Furthermore, it is easy to create an EL that provides phosphorescence from one EL layer and fluorescence from the other. This structure can be combined with any of the EL layer structures described above.

[0089] Furthermore, by designing the emission colors of the EL layers differently, it is possible to achieve a desired color of light emission from the light-emitting element as a whole. For example, the emission colors of the first and second EL layers in a light-emitting element containing both EL layers are complementary, so that the light-emitting element as a whole emits white light. The same applies to a light-emitting element with three or more EL layers.

[0090] As in Fig.As illustrated in Figure 15C, the EL layer 102 can include the hole injection layer 701, the hole transport layer 702, the light-emitting layer 703, the electron transport layer 704, an electron injection buffer layer 706, an electron relay layer 707, and a composite material layer 708, which is in contact with the second electrode 108, between the first electrode 103 and the second electrode 108.

[0091] Preferably, the composite material layer 708 is provided in contact with the second electrode 108, in which case damage caused to the EL layer 102 can be reduced, particularly if the second electrode 108 is formed by a sputtering process. The composite material layer 708 can be formed using the composite material described above, in which an organic compound exhibiting high hole transport capacity contains an acceptor substance.

[0092] Furthermore, by providing the electron injection buffer layer 706, an injection barrier between the composite material layer 708 and the electron transport layer 704 can be reduced; in this way, electrons generated in the composite material layer 708 can be easily injected into the electron transport layer 704.

[0093] The electron injection buffer layer 706 can be formed using a substance with a high electron injection capability, such as an alkali metal, an alkaline earth metal, a rare earth metal, a compound of the above metals (e.g., an alkali metal compound (for example, an oxide such as lithium oxide, a halide and a carbonate such as lithium carbonate or cesium carbonate), an alkaline earth metal compound (for example, an oxide, a halide and a carbonate) or a rare earth metal compound (for example, an oxide, a halide and a carbonate).

[0094] If the electron injection buffer layer 706 further contains a substance with a high electron transport capacity and a donor substance, the donor substance is preferably added such that the mass ratio of the donor substance to the substance with the high electron transport capacity is in the range of 0.001:1 to 0.1:1. It should be noted that an organic compound such as tetrathianaphthacene (abbreviation: TTN), nickelocene, or decamethylnickelocene, as well as an alkali metal, an alkaline earth metal, a rare earth metal, a compound of the above metals (e.g., an alkali metal compound (for example, an oxide such as lithium oxide, a halide, and a carbonate such as lithium carbonate or cesium carbonate), an alkaline earth metal compound (for example, an oxide, a halide, and a carbonate), and a rare earth metal compound (for example, an oxide, a halide, and a carbonate)) can be used as a donor substance.It should be noted that a material similar to the material described above for the electron transport layer 704 can be used as a substance with a high electron transport capacity.

[0095] Furthermore, the electron relay layer 707 is preferably formed between the electron injection buffer layer 706 and the composite material layer 708. The electron relay layer 707 is not necessarily provided; however, by providing the electron relay layer 707 with a high electron transport capacity, electrons can be rapidly transported to the electron injection buffer layer 706.

[0096] In the structure where the electron relay layer 707 is arranged between the composite material layer 708 and the electron injection buffer layer 706, it is less likely that the acceptor substance contained in the composite material layer 708 and the donor substance contained in the electron injection buffer layer 706 will interact with each other, and consequently their functions hardly interfere with each other. Therefore, an increase in the control voltage can be prevented.

[0097] The electron relay layer 707 contains a substance with a high electron transport capacity and is configured such that the LUMO level of the substance with the high electron transport capacity is between the LUMO level of the acceptor substance contained in the composite material layer 708 and the LUMO level of the substance with the high electron transport capacity contained in the electron transport layer 704. If the electron relay layer 707 contains a donor substance, the donor level of the donor substance is also controlled such that it is between the LUMO level of the acceptor substance contained in the composite material layer 708 and the LUMO level of the substance with the high electron transport capacity contained in the electron transport layer 704.The specific value of the energy level is the LUMO level of the substance with a high electron transport capacity, which is included in the electron relay layer 707, preferably higher than or equal to -5.0 eV, more preferably higher than or equal to -5.0 eV and lower than or equal to -3.0 eV.

[0098] A phthalocyanine-based material or a metal complex having a metal-oxygen bond and an aromatic ligand is preferably used as a substance with a high electron transport capacity that is included in the electron relay layer 707.

[0099] The phthalocyanine-based material incorporated in the electron relay layer 707 is particularly preferably alternatively CuPc, a phthalocyanine-tin(II) complex (SnPc), a phthalocyanine-zinc complex (ZnPc), cobalt(II) phthalocyanine, β-form (CoPc), phthalocyanine-iron (FePc) or vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (PhO-VOPc).

[0100] A metal complex containing a metal-oxygen bond and an aromatic ligand, which is included in the electron relay layer 707, is preferably used. The metal-oxygen double bond exhibits acceptor properties (the ability to readily accept electrons); in this way, electrons can be transferred (given and received) more easily. Furthermore, the metal complex containing a metal-oxygen double bond is considered stable. Consequently, the use of the metal complex containing the metal-oxygen double bond allows the light-emitting element to operate more stably at low voltage.

[0101] A phthalocyanine-based material is preferred as the metal complex, which features a metal-oxygen bond and an aromatic ligand. In particular, vanadyl phthalocyanine (VOPc), a phthalocyanine-tin(IV) oxide complex (SnOPc), or a phthalocyanine-titanium oxide complex (TiOPc) are preferred as alternatives, since a metal-oxygen double bond is likely to act on another molecule with respect to molecular structure and exhibits high acceptability.

[0102] It should be noted that, of the aforementioned phthalocyanine-based materials, a phthalocyanine-based material containing a phenoxy group is preferred. In particular, a phthalocyanine derivative containing a phenoxy group, such as PhO-VOPc, is preferred. The phthalocyanine derivative containing a phenoxy group is solvent-soluble and therefore has the advantage of being easy to handle during the formation of a light-emitting element and of simplifying the maintenance of a device used for film formation.

[0103] The electron relay layer 707 can also contain a donor substance. An organic compound such as tetrathianaphthacene (abbreviation: TTN), nickelocene, or decamethylnickelocene, as well as an alkali metal, an alkaline earth metal, a rare earth metal, or a compound of the above metals (e.g., an alkali metal compound (for example, an oxide such as lithium oxide, a halide, and a carbonate such as lithium carbonate or cesium carbonate), an alkaline earth metal compound (for example, an oxide, a halide, and a carbonate), and a rare earth metal compound (for example, an oxide, a halide, and a carbonate)) can be used as a donor substance. If such a donor substance is included in the electron relay layer 707, electrons can be transferred easily, and the light-emitting element can be operated at a lower voltage.

[0104] If a donor substance is included in the electron relay layer 707 that is different from the materials listed above as having a high electron transport capacity, a substance with a higher LUMO level than the acceptor substance included in the composite material layer 708 may be used. In particular, a substance with a LUMO level higher than or equal to -5.0 eV, preferably higher than or equal to -5.0 eV and lower than or equal to -3.0 eV, is preferably used. Examples of such a substance include a perylene derivative, a nitrogen-containing condensed aromatic compound, and the like. It should be noted that a nitrogen-containing condensed aromatic compound is preferably used for the electron relay layer 707 due to its high stability.

[0105] Specific examples of the perylene derivative include 3,4,9,10-perylenetetracarboxyl dianhydride (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxyl bis-benzimidazole (abbreviation: PTCBI), N,N'-dioctyl-3,4,9,10-perylenetetracarboxyl diimide (abbreviation: PTCDI-C8H), N,N'-dihexyl-3,4,9,10-perylenetetracarboxyl diimide (abbreviation: Hex PTC) and the like.

[0106] Specific examples of nitrogen-containing condensed aromatic compounds include pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation: PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT(CN)6), 2,3-diphenylpyrido[2,3-b]pyrazine (abbreviation: 2PYPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (abbreviation: F2PYPR) and the like.

[0107] In addition, 7,7,8,8-tetracyanoquinodimethane (abbreviation: TCNQ), 1,4,5,8-naphthalenetetracarboxylic dianhydride (abbreviation: NTCDA), perfluoropentacene, copper hexadecafluorophthalocyanine (abbreviation: F) can be used. 16CuPc), N,N'-Bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl)-1,4,5,8-naphthalenetetracarboxyl-diimide (abbreviation: NTCDI-C8F), 3',4'-Dibutyl-5,5''-bis(dicyanomethylene)-5,5''-dihydro-2,2':5',2''-terthiophene (abbreviation: DCMT), Methanefullerenes (e.g. [6,6]-Phenyl-C 61 -methyl butyric acid esters) or the like.

[0108] It should be noted that if a donor substance is included in the electron relay layer 707, the electron relay layer 707 can be formed by a process such as co-evaporation of the substance with a high electron transport capacity and the donor substance.

[0109] The hole injection layer 701, the hole transport layer 702, the light emitting layer 703 and the electron transport layer 704 can each be formed using the materials described above.

[0110] The EL layer 102 of this embodiment can be formed as described above.

[0111] In the light-emitting element described above, a current flows due to a potential difference generated between the first electrode 103 and the second electrode 108, and holes and electrons recombine in the EL layer 102, thus emitting light. This light emission is then extracted to the outside either through the first electrode 103 or the second electrode 108, or both. Therefore, either the first electrode 103 or the second electrode 108, or both, is an electrode capable of transmitting visible light.

[0112] It should be noted that the structure of layers provided between the first electrode 103 and the second electrode 108 is not limited to the structure described above. Alternatively, a different structure than the one above can be used, provided that a light-emitting region, in which holes and electrons recombine, is provided in a section away from the first electrode 103 and the second electrode 108 to prevent quenching due to the proximity of the light-emitting region to metal.

[0113] In other words, there is no particular restriction regarding the stacking structure of the layers. A layer containing a substance with high electron transport capability, a substance with high hole transport capability, a substance with high electron injection capability, a substance with high hole injection capability, a bipolar substance (a substance with both high electron and high hole transport capability), a hole-blocking material, or the like, can be combined with a light-emitting layer as desired.

[0114] By using the light-emitting element described in this embodiment, a passive matrix light-emitting device or an active matrix light-emitting device can be manufactured, in which the activation of the light-emitting element is controlled by a transistor. Furthermore, the light-emitting device can be used for an electronic device, a lighting device, or the like.

[0115] The light-emitting element of an embodiment of the present invention can be manufactured in the manner described above.

[0116] It should be noted that this embodiment can optionally be combined with the other embodiment. [Example 1]

[0117] Example 1 presents guest materials and a host material that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 1A and Fig. 1B and Fig. 16 dar.

[0118] The guest materials used in this example are the following three types: (Acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), Bis(3,5-dimethyl-2-phenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]) and (Acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]). The host material used in this example is a mixture of 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) and 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP). Chemical formulas of the materials used in this example are shown below.

[0119] (Measurement results of absorption spectra of guest materials and an emission spectrum of a host material) (Absorption spectra)

[0120] Fig. 1A and Fig. Figure 16 shows an ultraviolet-visible absorption spectrum (hereinafter referred to simply as the absorption spectrum) of [Ir(dppm)2(acac)] in a dichloromethane solution of [Ir(dppm)2(acac)] as absorption spectrum 1. Similarly, they show Fig. 1A and Fig. 16 also an absorption spectrum of [Ir(mppr-Me)2(dpm)] in a dichloromethane solution of [Ir(mppr-Me)2(dpm)] as absorption spectrum 2 and an absorption spectrum of [Ir(mppm)2(acac)] in a dichloromethane solution of [Ir(mppm)2(acac)] as absorption spectrum 3.

[0121] Measurements of the respective absorption spectra were carried out at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solutions in quartz cuvettes. (Emission spectrum)

[0122] Fig. 1A and Fig.Figure 16 also shows an emission spectrum of a thin film of a material mixture of 2mDBTPDBq-II and PCBA1BP. Fig. 1A represents the horizontal axis as the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig. 16 the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0123] Fig. 1A and Fig.Figure 16 shows that absorption spectra 1 to 3 each overlap the emission spectrum. In this way, it is shown that a light-emitting element comprising a light-emitting layer, in which any of the guest materials of this example and the host material of this example are used together, has a high energy transfer efficiency, since energy is transferred by means of the overlap of the emission spectrum of the host material and the absorption spectrum of the guest material.

[0124] Here in Fig. 1A and Fig.Sixteen maxima of absorption bands on the longest wavelength side (the side of lowest energy) (absorption bands that are thought to contribute significantly to light emission) in the absorption spectra and one maximum of the emission spectrum are considered. Of the maxima of absorption spectra 1 to 3, the maximum of absorption spectrum 1 is closest to the maximum of the emission spectrum, and the maximum of absorption spectrum 3 is furthest from the maximum of the emission spectrum.

[0125] Specifically, it amounts to Fig. 16 the difference between the maximum of absorption spectrum 1 and the maximum of emission spectrum is 0.02 eV, the difference between the maximum of absorption spectrum 2 and the maximum of emission spectrum is 0.12 eV, and the difference between the maximum of absorption spectrum 3 and the maximum of emission spectrum is 0.23 eV.

[0126] Next, the molar absorption coefficients at the maxima of the absorption bands on the longest wavelength side (the side of lowest energy) in the absorption spectra are determined. Fig. 1A is considered. Of the absorption spectra 1 to 3, absorption spectrum 1 has the highest molar absorption coefficient, and absorption spectrum 2 has the lowest molar absorption coefficient.

[0127] This means that of the absorption spectra 1 to 3, absorption spectrum 1 has the maximum of the absorption band on the longest wavelength side (the side of lowest energy), which is closest to the maximum of the emission spectrum, and the highest molar absorption coefficient at the maximum.

[0128] From the above, it follows that the absorption spectrum 1 overlaps the emission spectrum particularly strongly. Therefore, it is evident that a light-emitting element containing a material mixture of 2mDBTPDBq-II and PCBA1BP as the host material and [Ir(dppm)2(acac)] as the guest material exhibits a particularly high energy transfer efficiency, since energy is transferred via the overlap of the emission spectrum of the material mixture and the absorption spectrum of [Ir(dppm)2(acac)]. (Calculation results of absorption spectra of guest materials)

[0129] Next, a reproduction of the absorption spectra of [Ir(dppm)2(acac)] and [Ir(mppr-Me)2(dpm)] (the absorption spectra 1 and 2 in Fig. 1A), which had been obtained through the above measurements, were attempted to be calculated.

[0130] To obtain the absorption spectra of [Ir(dppm)2(acac)] and [Ir(mppr-Me)2(dpm)], excitation energies and oscillator intensities were calculated using the most stable structures of the respective molecules in their ground states. The absorption spectra were then obtained based on these calculated oscillator intensities. The specific calculation methods are described below.

[0131] The most stable ground-state structures of [Ir(dppm)2(acac)] and [Ir(mppr-Me)2(dpm)] were calculated using density functional theory (DFT). Next, the excitation energies and oscillator intensities of [Ir(dppm)2(acac)] and [Ir(mppr-Me)2(dpm)] were obtained using time-dependent density functional theory (TD-DFT), and their absorption spectra were calculated using these results. In DFT, the total energy is represented as the sum of the potential energy, the electrostatic energy between electrons, the electronic kinetic energy, and the exchange-correlation energy, which encompasses all the complex interactions between electrons.Furthermore, in DFT, an exchange-correlation interaction is approximated by a functional (that is, a function of another function) of an electron potential represented by an electron density, in order to enable highly accurate calculations. Here, B3PW91, a hybrid functional, was used to specify the weighting of each parameter with respect to the exchange-correlation energy. Additionally, LanL2DZ was applied as a basis function to Ir atoms, while 6-311 (the basis function of a triple-split valence basis set using three contraction functions for each valence orbital) was applied to atoms other than Ir atoms. The basis function above includes, for example, the 1s to 3s orbitals for hydrogen atoms and the 1s to 4s and 2p to 4p orbitals for carbon atoms.To improve the computational accuracy, the p-function and the d-function were added as polarization basis sets for hydrogen atoms and atoms other than hydrogen atoms, respectively.

[0132] It should be noted that Gaussian 09 was used as the quantum chemistry calculation program. A high-performance computer (Altix 4700, manufactured by SGI Japan, Ltd.) was used for the calculations.

[0133] Fig. Figure 1B shows the absorption spectra obtained through the calculations. For comparison, it shows Fig.1B also presents the absorption spectra obtained by the measurements described above. In particular, the absorption spectrum of [Ir(dppm)2(acac)] obtained by the measurements is shown as Absorption Spectrum 1, and the absorption spectrum obtained by the calculations is shown as Absorption Spectrum 1'. Furthermore, the absorption spectrum of [Ir(mppr-Me)2(dpm)] obtained by the measurements is shown as Absorption Spectrum 2, and the absorption spectrum obtained by the calculations is shown as Absorption Spectrum 2'. In Fig. In 1B, the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0134] As in Fig.As shown in Figure 1B, the absorption spectra 1 and absorption spectra 2 obtained by measurement exhibit essentially the same shapes as the absorption spectra 1' and 2' obtained by calculation. In particular, the following two tendencies of absorption spectra 1 and 2 are also evident in absorption spectra 1' and 2'.

[0135] Tendency 1: The maximum wavelength of the absorption spectrum 1 (1') is closer to the maximum wavelength of the emission spectrum than the maximum wavelength of the absorption spectrum 2 (2').

[0136] Trend 2: Absorption spectrum 1 (1') exhibits a higher molar absorption coefficient at the maximum wavelength of the absorption band on its longest wavelength side than absorption spectrum 2 (2'). [Example 2]

[0137] Example 2 presents a light-emitting element of an embodiment of the present invention with reference to Fig. 2. Chemical formulas of materials used in this example are shown below. Note that the chemical formulas of the materials used in the examples above are omitted here.

[0138] The following describes a method for manufacturing light-emitting elements 1 to 3 of this example. (Light-emitting element 1)

[0139] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 1100 by a sputtering process, thus forming a first electrode 1101, which served as the anode. The thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0140] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0141] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4 The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0142] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4Pa was reduced. Then, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and molybdenum(VI) oxide were co-evaporated over the first electrode 1101, forming a hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of BPAFLP to molybdenum oxide was adjusted to 4:2 (= BPAFLP:molybdenum oxide).

[0143] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that a hole transport layer 1112 was formed.

[0144] Furthermore, 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)2(acac)] were co-deposited to form a light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to PCBA1BP and [Ir(dppm)2(acac)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCBA1BP:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm.

[0145] Next, a 2mDBTPDBq-II film with a thickness of 10 nm was formed over the light-emitting layer 1113, thus forming a first electron transport layer 1114a.

[0146] Next, a bathophene anthroline (abbreviation: BPhen) film with a thickness of 20 nm was formed over the first electron transport layer 1114a, so that a second electron transport layer 1114b was formed.

[0147] Furthermore, a lithium fluoride (LiF) film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that an electron injection layer 1115 was formed.

[0148] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating a second electrode 1103 that served as the cathode. In this way, the light-emitting element 1 of this example was fabricated. (Light-emitting element 2)

[0149] The light-emitting layer 1113 of light-emitting element 2 was formed by co-evaporation of 2mDBTPDBq-II, PCBA1BP, and [Ir(mppr-Me)2(dpm)]. The weight ratio of 2mDBTPDBq-II to PCBA1BP and [Ir(mppr-Me)2(dpm)] was set to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCBA1BP:[Ir(mppr-Me)2(dpm)]). The thickness of light-emitting layer 1113 was 40 nm. The layers other than light-emitting layer 1113 were formed in the same way as those of light-emitting element 1. (Light-emitting element 3)

[0150] The light-emitting layer 1113 of light-emitting element 3 was formed by co-evaporation of 2mDBTPDBq-II, PCBA1BP, and [Ir(mppm)2(acac)]. The weight ratio of 2mDBTPDBq-II to PCBA1BP and [Ir(mppm)2(acac)] was set to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCBA1BP:[Ir(mppm)2(acac)]). The thickness of light-emitting layer 1113 was 40 nm. The layers other than light-emitting layer 1113 were formed in the same way as those of light-emitting element 1.

[0151] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0152] Table 1 shows the element structures of the light-emitting elements 1 to 3 obtained in this way. [Table 1] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2nd electron transport layer Electron injection layer 2nd electrode Light-emitting element 1 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-ll:PCBA1BP:[Ir(dppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm Light-emitting element 2 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:PCBA1BP:[Ir(mppr-Me)2(dpm)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm Light-emitting element 3 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-ll:PCBA1BP:[Ir(mppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm

[0153] These light-emitting elements were enclosed in a glove box containing a nitrogen atmosphere to prevent their exposure to air. The operating characteristics of these light-emitting elements were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0154] Fig. Figure 3 represents a current density-luminance characteristic curve of the light-emitting elements 1 to 3. Fig. 3. The horizontal axis represents the current density (mA / cm²). 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 4 represents a voltage-luminance characteristic curve. Fig. 4. The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 5 represents a luminance-current efficiency characteristic curve. Fig.5 represents the horizontal axis and the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 6 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 6 represents the horizontal axis and the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0155] Furthermore, Table 2 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current efficiency (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting elements 1 to 3 at a luminance of approximately 1,000 cd / m² 2 dar. [Table 2] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Luminance (cd / m²) 2 ) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 1 3,0 1,3 (0,56, 0,44) 840 65 68 26 Light-emitting element 2 3,0 1,6 (0,55, 0,45) 1.000 63 66 24 Light-emitting element 3 3,0 1,3 (0,44, 0,55) 940 77 76 20

[0156] Fig. Figure 7 shows the emission spectra of light-emitting elements 1 to 3, obtained by applying a current of 0.1 mA. Fig.Figure 7 represents the horizontal axis as the wavelength (nm), and the vertical axis as the emission intensity (arbitrary unit). As shown in Table 2, the CIE chromaticity coordinates of light-emitting element 1 (x, y) = (0.56, 0.44) at a luminance of 840 cd / m² 2 , the CIE chromaticity coordinates of the light-emitting element 2 were (x, y) = (0.55, 0.45) at a luminance of 1,000 cd / m² 2 , and the CIE chromaticity coordinates of light-emitting element 3 were (x, y) = (0.44, 0.55) at a luminance of 940 cd / m² 2 The results show that light-emitting element 1 emits light originating from [Ir(dppm)2(acac)], light-emitting element 2 emits light originating from [Ir(mppr-Me)2(dpm)], and light-emitting element 3 emits light originating from [Ir(mppm)2(acac)].

[0157] As shown in Table 2 and Fig. 3, Fig. 4, Fig. 5 to Fig.As can be seen in Figure 6, each of the light-emitting elements 1 to 3 exhibits a high current yield, a high efficiency, and a high external quantum efficiency.

[0158] In the light-emitting elements of this example, the light-emitting layers contain the host material and the guest materials described in Example 1. As described in Example 1, the respective absorption spectra of the guest materials contained in light-emitting elements 1 to 3 overlap the emission spectrum of the host material. The light-emitting elements of this example are considered to exhibit high energy transfer efficiency and external quantum efficiency, as energy is transferred via these overlaps.

[0159] Furthermore, light-emitting element 1 exhibits a higher external quantum efficiency than light-emitting elements 2 and 3. According to the results in Example 1, the maximum of the absorption band on the side of lowest energy in the absorption spectrum of the guest material contained in light-emitting element 1 is closest to the maximum of the emission spectrum (the difference between the maxima is 0.02 eV), and the molar absorption coefficient at the maximum wavelength is the highest (> 5,000 M). -1 ·cm -1 ). Consequently, it is shown that the particularly high energy transfer efficiency of the light-emitting element 1 results in the high external quantum efficiency.

[0160] Furthermore, light-emitting element 2 exhibits a higher external quantum efficiency than light-emitting element 3. According to the results in Example 1, the maximum wavelength of the absorption spectrum of element 2 is closer to the maximum wavelength of the emission spectrum than the maximum wavelength of the absorption spectrum of element 3. Consequently, it is shown that this is the reason why the external quantum efficiency characteristics of light-emitting elements 2 and 3 differ.

[0161] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency.

[0162] Next, reliability tests were carried out on the light-emitting elements 1 to 3. Fig. Section 8 presents the results of the reliability checks. Fig.Figure 8 represents the vertical axis as the normalized luminance (%) assuming an initial luminance of 100%, and the horizontal axis represents the driving time (h) of the elements.

[0163] During the reliability tests, the light-emitting elements 1 to 3 were each driven under conditions where the initial luminance was set to 5,000 cd / m². 2 was determined and the current density was constant.

[0164] After driving for over 470 hours, light-emitting element 1 retained 85% of its initial luminance. After driving for over 470 hours, light-emitting element 2 retained 72% of its initial luminance. After driving for over 280 hours, light-emitting element 3 retained 72% of its initial luminance.

[0165] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a long lifetime. [Example 3]

[0166] Example 3 presents a light-emitting element of an embodiment of the present invention with reference to Fig. 2. The materials used in this example are also used in the examples above, and therefore their chemical formulas are omitted here.

[0167] The following describes a method for manufacturing a light-emitting element 4 of this example. (Light-emitting element 4)

[0168] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over the glass substrate 1100 by a sputtering process, thus forming the first electrode 1101, which served as the anode. The thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0169] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0170] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4 The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0171] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4 Pa was reduced. Then, BPAFLP and molybdenum(VI) oxide were co-evaporated over the first electrode 1101 to form the hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of BPAFLP to molybdenum oxide was adjusted to 4:2 (= BPAFLP:molybdenum oxide).

[0172] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that the hole transport layer 1112 was formed.

[0173] Furthermore, 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)2(acac)] were co-deposited to form the light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to PCBA1BP and [Ir(dppm)2(acac)] was adjusted to 0.8:0.2:0.1 (= 2mDBTPDBq-II:PCBA1BP:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm.

[0174] Next, a 2mDBTPDBq-II film with a thickness of 15 nm was formed over the light-emitting layer 1113, thus forming the first electron transport layer 1114a.

[0175] Next, a Bphen film with a thickness of 15 nm was formed over the first electron transport layer 1114a, so that the second electron transport layer 1114b was formed.

[0176] Furthermore, a LiF film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that the electron injection layer 1115 was formed.

[0177] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating the second electrode 1103, which served as the cathode. In this way, the light-emitting element 4 of this example was fabricated.

[0178] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0179] Table 3 shows the elemental structures of the light-emitting element 4 obtained in this way. [Table 3] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2nd electron transport layer Electron injection layer 2nd electrode Light-emitting element 4 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:PCBA1BP:[Ir(dppm)2(acac)](= 0.8:0.2:0.1)40 nm 2mDBTP DBq-II15 nm Bphen15 nm LiF1 nm Al200 nm

[0180] The light-emitting element 4 was enclosed in a glove box containing a nitrogen atmosphere to prevent its exposure to air. The operating characteristics of the light-emitting element were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0181] Fig. Figure 9 represents a current density-luminance characteristic curve of the light-emitting element 4. Fig. 9 represents the current density (mA / cm²) on the horizontal axis. 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 10 represents a voltage-luminance characteristic curve. Fig. 10. The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 11 represents a luminance-current efficiency characteristic curve. Fig.11 The horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 12 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 12 The horizontal axis represents the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0182] Furthermore, Table 4 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current yield (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting element 4 at a luminance of approximately 1,100 cd / m² 2 dar. [Table 4] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 4 3,0 1,4 (0,57, 0,43) 76 70 31

[0183] Fig. Figure 13 represents an emission spectrum of the light-emitting element 4, obtained by applying a current of 0.1 mA. Fig.Figure 13 shows that the horizontal axis represents the wavelength (nm), and the vertical axis represents the emission intensity (arbitrary unit). As shown in Table 4, the CIE chromaticity coordinates of light-emitting element 4 (x, y) = (0.57, 0.43) at a luminance of 1100 cd / m². 2 The results show that the light-emitting element 4 emits light originating from [Ir(dppm)2(acac)].

[0184] As shown in Table 4 and Fig. 9, Fig. 10, Fig. 11 to Fig. As can be seen in Figure 12, the light-emitting element 4 exhibits a high current output, a high efficiency, and a high external quantum efficiency. In particular, the light-emitting element 4 exhibits an extremely high external quantum efficiency at a luminance of 1,100 cd / m². 2 The result is 31%. As described above, the limit for external quantum efficiency is approximately 25%. However, the result is beyond this limit.

[0185] In the light-emitting element of this example, the light-emitting layer includes the host material and the guest material described in Example 1. As described in Example 1, the absorption spectrum of the guest material contained in light-emitting element 4 overlaps the emission spectrum of the host material. The light-emitting element of this example is considered to have high energy transfer efficiency and external quantum efficiency because energy is transferred via the overlap.

[0186] According to the results in Example 1, the maximum wavelength of the absorption band on the longest wavelength side in the absorption spectrum of the guest material contained in the light-emitting element 4 is close to the maximum wavelength of the emission spectrum (the difference between the maxima is 0.02 eV), and the molar absorption coefficient at the maximum wavelength is high (> 5,000 M). -1 ·cm -1 ). Consequently, it is shown that the particularly high energy transfer efficiency of the light-emitting element 4 results in the new high external quantum efficiency.

[0187] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency.

[0188] Next, reliability tests were carried out on light-emitting element 4. Fig. Section 14 presents the results of the reliability checks. Fig. Figure 14 represents the vertical axis as the normalized luminance (%) assuming an initial luminance of 100%, and the horizontal axis represents the drive duration (h) of the element.

[0189] During the reliability tests, the light-emitting element 4 was driven under conditions where the initial luminance was set to 5,000 cd / m². 2 was determined and the current density was constant.

[0190] After being driven for over 170 hours, the light-emitting element 4 retained 95% of its initial luminance.

[0191] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with high reliability. [Example 4]

[0192] Example 4 provides examples of a guest material and a host material that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 17A and Fig. 17B.

[0193] The guest material used in this example is [Ir(dppm)2(acac)]. The host material also used in this example is a mixture of 2mDBTPDBq-II and 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB). A chemical formula of one of the materials used in this example is shown below. Note that the chemical formulas of the materials used in the examples above are omitted here. (Absorption spectrum)

[0194] Fig. 17A and Fig.Figure 17B shows an ultraviolet visible absorption spectrum (absorption spectrum a) of [Ir(dppm)2(acac)] in a dichloromethane solution of [Ir(dppm)2(acac)]. Absorption spectrum measurements were performed at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solution (0.093 mmol / L) in a quartz cuvette. (Emission spectrum)

[0195] Fig. 17A and Fig. Figure 17B also shows an emission spectrum (emission spectrum a) of a thin film of a material mixture of 2mDBTPDBq-II and NPB. Fig. 17A the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig. In 17B, the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M-1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0196] The absorption spectrum a in Fig. Figure 17A shows that [Ir(dppm)2(acac)] has a broad absorption band around 520 nm. This absorption band is thought to contribute significantly to light emission.

[0197] It turns out that the maximum of the emission spectrum a and the absorption band in the absorption spectrum a, which is thought to contribute significantly to light emission, exhibit strong overlap. Specifically, the difference between the maximum (515 nm) of the absorption band in the absorption spectrum a and the maximum of the emission spectrum a is 0.09 eV. Thus, it is shown that a light-emitting element incorporating a light-emitting layer, where the guest material and the host material of this example are used together, has a high energy transfer efficiency, since energy is transferred via the overlap of the host material's emission spectrum and the guest material's absorption spectrum. Therefore, it is shown that a light-emitting element with high external quantum efficiency can be achieved. [Example 5]

[0198] Example 5 presents a light-emitting element of an embodiment of the present invention with reference to Fig. Figure 2. The following is a chemical formula of a material used in this example. Note that the chemical formulas of the materials used in the examples above are omitted here.

[0199] The following describes a method for manufacturing a light-emitting element 5 of this example. (Light-emitting element 5)

[0200] First, an ITSO film was formed over the glass substrate 1100 by a sputtering process, thus forming the first electrode 1101, which served as the anode. Its thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0201] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0202] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4 The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0203] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4Pa was reduced. Then, 4,4',4''-(1,3,5-benzenetriyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) and molybdenum(VI) oxide were co-evaporated over the first electrode 1101 to form the hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2 (= DBT3P-II:molybdenum oxide).

[0204] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that the hole transport layer 1112 was formed.

[0205] Furthermore, 2mDBTPDBq-II, NPB, and [Ir(dppm)2(acac)] were co-deposited to form the light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to NPB and [Ir(dppm)2(acac)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:NPB:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm.

[0206] Next, a 2mDBTPDBq-II film with a thickness of 10 nm was formed over the light-emitting layer 1113, thus forming the first electron transport layer 1114a.

[0207] Next, a Bphen film with a thickness of 20 nm was formed over the first electron transport layer 1114a, so that the second electron transport layer 1114b was formed.

[0208] Furthermore, a LiF film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that the electron injection layer 1115 was formed.

[0209] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating the second electrode 1103, which served as the cathode. In this way, the light-emitting element 5 of this example was fabricated.

[0210] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0211] Table 5 shows the elemental structures of the light-emitting element 5 obtained in this way. [Table 5] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2. Electron transport layer Electron injection layer 2nd electrode Light-emitting element 5 ITSO110 nm DBT3P-II:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:NPB:[Ir(dppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm

[0212] The light-emitting element 5 was enclosed in a glove box containing a nitrogen atmosphere to prevent its exposure to air. The operating characteristics of the light-emitting element were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0213] Fig. Figure 18 represents a current density-luminance characteristic curve of the light-emitting element 5. Fig. 18 The horizontal axis represents the current density (mA / cm²). 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2) dar. Fig. Figure 19 represents a voltage-luminance characteristic curve. Fig. 19 The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 20 represents a luminance-current efficiency characteristic curve. Fig. 20 The horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 21 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 21 represents the horizontal axis, the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0214] Furthermore, Table 6 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current yield (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting element 5 at a luminance of approximately 1,100 cd / m²2 dar. [Table 6] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 5 2,9 1,5 (0,57, 0,43) 75 81 29

[0215] Fig. Figure 22 represents an emission spectrum of the light-emitting element 5, obtained by applying a current of 0.1 mA. Fig. Figure 22 shows that the horizontal axis represents the wavelength (nm), and the vertical axis represents the emission intensity (arbitrary unit). As shown in Table 6, the CIE chromaticity coordinates of light-emitting element 5 (x, y) = (0.57, 0.43) at a luminance of 1100 cd / m². 2 The results show that the light-emitting element 5 emits light originating from [Ir(dppm)2(acac)].

[0216] As shown in Table 6 and Fig. 18, Fig. 19, Fig. 20 to Fig. As can be seen in Figure 21, the light-emitting element 5 has a high current yield, a high efficiency and a high external quantum efficiency.

[0217] In light-emitting element 5, the light-emitting layer comprises 2mDBTPDBq-II, NPB, and [Ir(dppm)2(acac)], as described in Example 4. As described in Example 4, the emission spectrum of the material mixture of 2mDBTPDBq-II and NPB and the absorption band largely overlap, with the latter expected to contribute significantly to light emission in the absorption spectrum of [Ir(dppm)2(acac)]. Light-emitting element 5 is considered to have high energy transfer efficiency and external quantum efficiency, as energy is transferred via the overlap.

[0218] According to the results in Example 4, the maximum of the absorption band on the longest wavelength side in the absorption spectrum of the guest material contained in the light-emitting element 5 is close to the maximum of the emission spectrum, and the molar absorption coefficient at the maximum is high (> 5,000 M). -1 ·cm -1 ). Consequently, it is shown that the particularly high energy transfer efficiency of the light-emitting element 5 results in the new high external quantum efficiency.

[0219] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency. [Example 6]

[0220] Example 6 provides examples of a guest material and a host material that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 23A and Fig. 23B.

[0221] The guest material used in this example is bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]). The host material also used in this example is a mixture of 2mDBTPDBq-II and NPB. A chemical formula of one of the materials used in this example is given below. Note that the chemical formulas of the materials used in the examples above are omitted here. (Absorption spectrum)

[0222] Fig. 23A and Fig.Figure 23B shows an ultraviolet visible absorption spectrum (absorption spectrum b) of [Ir(tppr)2(dpm)] in a dichloromethane solution of [Ir(tppr)2(dpm)]. Absorption spectrum measurements were performed at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solution (0.094 mmol / L) in a quartz cuvette. (Emission spectrum)

[0223] Fig. 23A and Fig. Figure 23B also shows an emission spectrum (emission spectrum b) of a thin film of a material mixture of 2mDBTPDBq-II and NPB. In Fig. 23A the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig. 23 B the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M-1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0224] The absorption spectrum b in Fig. Figure 23A shows that [Ir(tppr)2(dpm)] has a broad absorption band around 530 nm. This absorption band is thought to contribute significantly to light emission.

[0225] It turns out that the maximum of the emission spectrum b and the absorption band in the absorption spectrum b, which is thought to contribute significantly to light emission, exhibit strong overlap. Specifically, the difference between the maximum (peak at approximately 530 nm) of the absorption band in the absorption spectrum b and the maximum of the emission spectrum b is 0.01 eV. Thus, it is shown that a light-emitting element incorporating a light-emitting layer, where the guest material and the host material of this example are used together, has a high energy transfer efficiency, as energy is transferred via the overlap of the host material's emission spectrum and the guest material's absorption spectrum. Therefore, it is shown that a light-emitting element with high external quantum efficiency can be achieved. [Example 7]

[0226] Example 7 presents a light-emitting element of an embodiment of the present invention with reference to Fig. 2. The materials used in this example are also used in the examples above, and therefore their chemical formulas are omitted here.

[0227] The following describes a method for manufacturing a light-emitting element 6 of this example. (Light-emitting element 6)

[0228] The light-emitting layer 1113 of the light-emitting element 6 was formed by co-evaporation of 2mDBTPDBq-II, NPB, and [Ir(tppr)2(dpm)]. The weight ratio of 2mDBTPDBq-II to NPB and [Ir(tppr)2(dpm)] was set to 0.8:0.2:0.05 (= 2mDBTPDBq-II:NPB:[Ir(tppr)2(dpm)]). The thickness of the light-emitting layer 1113 was 40 nm. Apart from the light-emitting layer 1113, the light-emitting element 6 was fabricated in a similar manner to the light-emitting element 5 described in Example 5.

[0229] Table 7 shows the elemental structures of the light-emitting element 6 obtained in this way. [Table 7] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2. Electron transport layer Electron injection layer 2nd electrode Light-emitting element 6 ITSO110 nm DBT3P-II:MoOx (= 4:2)40 nm BPAFLP 20 nm 2mDBTPDBq-II:NPB:[Ir(tppr)2(dpm)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm

[0230] The light-emitting element 6 was enclosed in a glove box containing a nitrogen atmosphere to prevent its exposure to air. The operating characteristics of the light-emitting element were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0231] Fig. Figure 24 represents a current density-luminance characteristic curve of the light-emitting element 6. Fig. 24 the horizontal axis represents the current density (mA / cm²). 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 25 represents a voltage-luminance characteristic curve. Fig. In diagram 25, the horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 26 represents a luminance-current efficiency characteristic curve. Fig.26 the horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 27 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 27 the horizontal axis represents the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0232] Furthermore, Table 8 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current yield (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting element 6 at a luminance of approximately 1,100 cd / m² 2 dar. [Table 8] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 6 3,3 4,1 (0,66, 0,34) 26 25 22

[0233] Fig. Figure 28 represents an emission spectrum of the light-emitting element 6, obtained by applying a current of 0.1 mA. Fig.Figure 28 shows that the horizontal axis represents the wavelength (nm), and the vertical axis represents the emission intensity (arbitrary unit). As shown in Table 8, the CIE chromaticity coordinates of the light-emitting element 6 (x, y) = (0.66, 0.34) at a luminance of 1100 cd / m². 2 The results show that the light-emitting element 6 emits light originating from [Ir(tppr)2(dpm)].

[0234] As shown in Table 8 and Fig. 24, Fig. 25, Fig. 26 to Fig. As can be seen in Figure 27, the light-emitting element 6 has a high current yield, a high efficiency and a high external quantum efficiency.

[0235] In light-emitting element 6, the light-emitting layer comprises 2mDBTPDBq-II, NPB, and [Ir(tppr)2(dpm)], as described in Example 6. As described in Example 6, the emission spectrum of the material mixture of 2mDBTPDBq-II and NPB and the absorption band largely overlap, with the latter expected to contribute significantly to light emission in the absorption spectrum of [Ir(tppr)2(dpm)]. Light-emitting element 6 is considered to have high energy transfer efficiency and external quantum efficiency, as energy is transferred via the overlap.

[0236] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency.

[0237] Next, reliability tests were carried out on light-emitting element 6. Fig.Section 29 presents the results of the reliability checks. Fig. 29 The vertical axis represents the normalized luminance (%) assuming an initial luminance of 100%, and the horizontal axis represents the driving time (h) of the element.

[0238] During the reliability tests, the light-emitting element 6 was driven under conditions where the initial luminance was set to 5,000 cd / m². 2 was determined and the current density was constant.

[0239] After being driven for over 98 hours, light-emitting element 6 retained 87% of its initial luminance. The results indicate that light-emitting element 6 has a long lifetime.

[0240] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with high reliability. [Example 8]

[0241] Example 8 presents examples of a guest material and host materials that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 30A and Fig. 30B.

[0242] The guest material used in this example is [Ir(mppm)2(acac)]. The host materials also used in this example are the following two types: a mixture of 2mDBTPDBq-II and PCBA1BP, and a mixture of 2mDBTPDBq-II and 4-(1-naphthyl)-4'-phenyltriphenylamine (abbreviated αNBA1BP). A chemical formula of one of the materials used in this example is shown below. Note that the chemical formulas of the materials used in the examples above are omitted here. (Absorption spectrum)

[0243] Fig. 30A and Fig.Figure 30B shows an ultraviolet visible absorption spectrum (absorption spectrum c) of [Ir(mppm)2(acac)] in a dichloromethane solution of [Ir(mppm)2(acac)]. Absorption spectrum measurements were performed at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solution (0.10 mmol / L) in a quartz cuvette. (Emission spectra)

[0244] Fig. 30A and Fig. 30B also presents an emission spectrum (emission spectrum c-1) of a thin film of a material mixture of 2mDBTPDBq-II and PCBA1BP and an emission spectrum (emission spectrum c-2) of a thin film of a material mixture of 2mDBTPDBq-II and αNBA1 BP. In Fig. 30A, the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig.In 30 B, the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0245] The absorption spectrum c in Fig. Figure 30A shows that [Ir(mppm)2(acac)] has a broad absorption band around 490 nm. This absorption band is thought to contribute significantly to light emission.

[0246] It turns out that each of the maxima of the emission spectra c-1 and c-2 and the absorption band in the absorption spectrum c, which is assumed to contribute significantly to light emission, exhibit strong overlap. In this way, it is shown that a light-emitting element incorporating a light-emitting layer, where the guest material and one of the host materials of this example are used together, has a high energy transfer efficiency, since energy is transferred via the overlap of the emission spectrum of the host material and the absorption spectrum of the guest material. Therefore, it is shown that a light-emitting element with high external quantum efficiency can be achieved.

[0247] Here, the emission spectrum c-2 exhibits a maximum on a shorter wavelength side (higher energy side) than the emission spectrum c-1. The maximum of the emission spectrum c-2 is closer to the absorption band mentioned above than the maximum of the emission spectrum c-1. In particular, the difference between the maximum of the absorption band in the absorption spectrum c (located at approximately 490 nm) and the maximum of the emission spectrum c-1 is 0.15 eV, and the difference between the maximum of the absorption band in the absorption spectrum c (located at approximately 490 nm) and the maximum of the emission spectrum c-2 is 0.01 eV.

[0248] The difference between the maxima of the emission spectra c-1 and c-2 is thought to be due to the difference between the HOMO levels of PCBA1BP and αNBA1BP. Specifically, the HOMO level of PCBA1BP is -5.43 eV, whereas the HOMO level of αNBA1BP is -5.52 eV (both values ​​were calculated by cyclic voltammetry (CV) measurements). It is thought that, since αNBA1BP has a lower HOMO level than PCBA1BP, the maximum of the emission spectrum c-2 is located on a shorter wavelength side (higher energy side) than the maximum of the emission spectrum c-1. [Example 9]

[0249] Example 9 presents a light-emitting element of an embodiment of the present invention with reference to Fig. 2. The materials used in this example are also used in the examples above, and therefore their chemical formulas are omitted here.

[0250] The following describes a method for manufacturing light-emitting elements 7 and 8 of this example. (Light-emitting element 7)

[0251] First, an ITSO film was formed over the glass substrate 1100 by a sputtering process, thus forming the first electrode 1101, which served as the anode. Its thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0252] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0253] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0254] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4 Pa was reduced. Then, BPAFLP and molybdenum(VI) oxide were co-evaporated over the first electrode 1101 to form the hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of BPAFLP to molybdenum oxide was adjusted to 4:2 (= BPAFLP:molybdenum oxide).

[0255] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that the hole transport layer 1112 was formed.

[0256] Furthermore, 2mDBTPDBq-II, PCBA1BP, and [Ir(mppm)2(acac)] were co-deposited to form the light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to PCBA1BP and [Ir(mppm)2(acac)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCBA1BP:[Ir(mppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm.

[0257] Next, a 2mDBTPDBq-II film with a thickness of 10 nm was formed over the light-emitting layer 1113, thus forming the first electron transport layer 1114a.

[0258] Next, a Bphen film with a thickness of 20 nm was formed over the first electron transport layer 1114a, so that the second electron transport layer 1114b was formed.

[0259] Furthermore, a LiF film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that the electron injection layer 1115 was formed.

[0260] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating the second electrode 1103, which served as the cathode. In this way, the light-emitting element 7 of this example was fabricated. (Light-emitting element 8)

[0261] The light-emitting layer 1113 of the light-emitting element 8 was formed by co-evaporation of 2mDBTPDBq-II, αNBA1BP, and [Ir(mppm)2(acac)]. The weight ratio of 2mDBTPDBq-II to αNBA1BP and [Ir(mppm)2(acac)] was set to 0.8:0.2:0.05 (= 2mDBTPDBq-II:αNBA1BP:[Ir(mppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm. The layers other than the light-emitting layer 1113 were formed in the same way as those of the light-emitting element 7.

[0262] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0263] Table 9 shows the elemental structures of the light-emitting elements 7 and 8 obtained in this way. [Table 9] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2. Electron transport layer Electron injection layer 2nd electrode Light-emitting element 7 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:PCBA1BP:[Ir(mppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm Light-emitting element 8 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:áNBA1BP:[Ir(mppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm

[0264] These light-emitting elements were enclosed in a glove box containing a nitrogen atmosphere to prevent their exposure to air. The operating characteristics of these light-emitting elements were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0265] Fig. Figure 31 represents a current density-luminance characteristic curve of the light-emitting elements 7 and 8. Fig. Figure 31 represents the current density (mA / cm²) on the horizontal axis. 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 32 represents a voltage-luminance characteristic curve. Fig. 32 The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 33 represents a luminance-current efficiency characteristic curve. Fig.33 The horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 34 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 34 The horizontal axis represents the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0266] Furthermore, Table 10 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current efficiency (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting elements 7 and 8 at a luminance of approximately 1,000 cd / m² 2 dar. [Table 10] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Luminance (cd / m²) 2 ) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 7 3,2 1,6 (0,43, 0,56) 1.100 69 68 20 Light-emitting element 8 3,0 1,1 (0,43, 0,56) 860 75 79 21

[0267] Fig. Figure 35 presents emission spectra of the light-emitting elements 7 and 8, obtained by applying a current of 0.1 mA. Fig.Figure 35 shows that the horizontal axis represents the wavelength (nm), and the vertical axis represents the emission intensity (arbitrary unit). As shown in Table 10, the CIE chromaticity coordinates of light-emitting element 7 (x, y) = (0.43, 0.56) at a luminance of 1100 cd / m². 2 , and the CIE chromaticity coordinates of the light-emitting element 8 were (x, y) = (0.43, 0.56) at a luminance of 860 cd / m² 2 The results show that the light-emitting elements 7 and 8 emit a yellow-green light originating from [Ir(mppm)2(acac)].

[0268] As shown in Table 10 and Fig. 31, Fig. 32, Fig. 33 to Fig. As can be seen in Figure 34, each of the light-emitting elements 7 and 8 exhibits a high current yield, a high efficiency, and a high external quantum efficiency.

[0269] The light-emitting layer of light-emitting element 7 contains PCBA1BP, 2mDBTPDBq-II, and [Ir(mppm)2(acac)], as described in Example 8, and the light-emitting layer of light-emitting element 8 contains αNBA1BP, 2mDBTPDBq-II, and [Ir(mppm)2(acac)], as described in Example 8. As described in Example 8, the emission spectra of the material mixture of 2mDBTPDBq-II and PCBA1BP and the material mixture of 2mDBTPDBq-II and αNBA1BP show strong overlap with the absorption band in the absorption spectrum of [Ir(mppm)2(acac)], which is thought to contribute significantly to light emission. It is believed that the light-emitting elements 7 and 8 exhibit high energy transfer efficiency and external quantum efficiency, as energies are transferred using the overlaps.

[0270] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency.

[0271] Next, reliability tests were carried out on the light-emitting elements 7 and 8. Fig. Section 36 presents the results of the reliability checks. Fig. Figure 36 represents the vertical axis as the normalized luminance (%) assuming an initial luminance of 100%, and the horizontal axis represents the driving time (h) of the elements.

[0272] During the reliability tests, the light-emitting elements 7 and 8 were each driven under conditions where the initial luminance was set to 5,000 cd / m². 2 was determined and the current density was constant.

[0273] After being driven for over 260 hours, light-emitting element 7 retained 74% of its initial luminance. After being driven for over 260 hours, light-emitting element 8 retained 75% of its initial luminance. The results show that light-emitting elements 7 and 8 have a long lifetime.

[0274] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with high reliability. [Example 10]

[0275] Example 10 presents examples of a guest material and host materials that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 37A and Fig. 37B.

[0276] The guest material used in this example is (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]). The host materials also used in this example are the following two types: a mixture of 2mDBTPDBq-II and NPB, and a mixture of 2mDBTPDBq-II and 2,7-bis[N-(diphenylaminophenyl)-N-phenylamino]-spiro-9,9'-bifluorene (abbreviation: DPA2SF). Chemical formulas of the materials used in this example are given below. Note that the chemical formulas of the materials used in the examples above are omitted here. (Absorption spectrum)

[0277] Fig. 37A and Fig.Figure 37B shows an ultraviolet visible absorption spectrum (absorption spectrum d) of [Ir(tBuppm)2(acac)] in a dichloromethane solution of [Ir(tBuppm)2(acac)]. Absorption spectrum measurements were performed at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solution (0.093 mmol / L) in a quartz cuvette. (Emission spectra)

[0278] Fig. 37A and Fig. Figure 37B also presents an emission spectrum (emission spectrum d-1) of a thin film of a material mixture of 2mDBTPDBq-II and DPA2SF and an emission spectrum (emission spectrum d-2) of a thin film of a material mixture of 2mDBTPDBq-II and NPB. Fig. 37A the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig.37 B the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0279] The absorption spectrum d in Fig. Figure 37A shows that [Ir(tBuppm)2(acac)] has a broad absorption band around 490 nm. This absorption band is thought to contribute significantly to light emission.

[0280] It turns out that each of the maxima of the emission spectra d-1 and d-2 and the absorption band in the absorption spectrum d, which is assumed to contribute significantly to light emission, exhibit strong overlap. In this way, it is shown that a light-emitting element incorporating a light-emitting layer, where the guest material and one of the host materials of this example are used together, has a high energy transfer efficiency, since energy is transferred via the overlap of the emission spectrum of the host material and the absorption spectrum of the guest material. Therefore, it is shown that a light-emitting element with high external quantum efficiency can be achieved.

[0281] Here, the emission spectrum d-2 exhibits a maximum on a shorter wavelength side (higher energy side) than the emission spectrum d-1. The maximum of the emission spectrum d-2 is closer to the absorption band mentioned above than the maximum of the emission spectrum d-1. From the above in Fig. 37A and Fig. From Equation 37B, it follows that the emission spectrum exhibiting the strongest overlap with the absorption band in the absorption spectrum d, which contributes significantly to light emission, is the emission spectrum d-2. Specifically, the difference between the maximum of the absorption band in the absorption spectrum d and the maximum of the emission spectrum d-1 is 0.39 eV, and the difference between the maximum of the absorption band in the absorption spectrum d and the maximum of the emission spectrum d-2 is 0.19 eV.

[0282] The difference between the maxima of the emission spectra d-1 and d-2 is thought to be due to the difference between the HOMO levels of DPA2SF and NPB. Specifically, the HOMO level of DPA2SF is -5.09 eV, whereas the HOMO level of NPB is -5.38 eV (both values ​​were calculated by CV measurements). It is thought that, since NPB has a lower HOMO level than DPA2SF, the maximum of the emission spectrum d-2 is located on a shorter wavelength side (higher energy side) than the maximum of the emission spectrum d-1.

[0283] From the above, it follows that a light-emitting element comprising a light-emitting layer in which a material mixture of 2mDBTPDBq-II and NPB and [Ir(tBuppm)2(acac)] is used together exhibits a high energy transfer efficiency compared to a light-emitting element comprising a light-emitting layer in which a material mixture of 2mDBTPDBq-II and DPA2SF and [Ir(tBuppm)2(acac)] is used together, since energy is transferred via the strong overlap of the emission spectrum of the host material and the absorption spectrum of the guest material. Therefore, it is shown that a light-emitting element with a higher external quantum efficiency can be achieved. [Example 11]

[0284] Example 11 presents a light-emitting element of an embodiment of the present invention with reference to Fig.2. The materials used in this example are also used in the examples above, and therefore their chemical formulas are omitted here.

[0285] The following describes a method for manufacturing light-emitting elements 9 and 10 of this example. (Light-emitting element 9)

[0286] First, an ITSO film was formed over the glass substrate 1100 by a sputtering process, thus forming the first electrode 1101, which served as the anode. Its thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0287] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0288] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4 The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0289] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4Pa was reduced. Then, DBT3P-II and molybdenum(VI) oxide were co-evaporated over the first electrode 1101 to form the hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2 (= DBT3P-II:molybdenum oxide).

[0290] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that the hole transport layer 1112 was formed.

[0291] Furthermore, 2mDBTPDBq-II, DPA2SF, and [Ir(tBuppm)2(acac)] were co-deposited to form the light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to DPA2SF and [Ir(tBuppm)2(acac)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:DPA2SF:[Ir(tBuppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm.

[0292] Next, a 2mDBTPDBq-II film with a thickness of 10 nm was formed over the light-emitting layer 1113, thus forming the first electron transport layer 1114a.

[0293] Next, a Bphen film with a thickness of 20 nm was formed over the first electron transport layer 1114a, so that the second electron transport layer 1114b was formed.

[0294] Furthermore, a LiF film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that the electron injection layer 1115 was formed.

[0295] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating the second electrode 1103, which served as the cathode. In this way, the light-emitting element 9 of this example was fabricated. (Light-emitting element 10)

[0296] The light-emitting layer 1113 of the light-emitting element 10 was formed by co-evaporation of 2mDBTPDBq-II, NPB, and [Ir(tBuppm)2(acac)]. The weight ratio of 2mDBTPDBq-II to NPB and [Ir(tBuppm)2(acac)] was set to 0.8:0.2:0.05 (= 2mDBTPDBq-II:NPB:[Ir(tBuppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm. The layers other than the light-emitting layer 1113 were formed in the same way as those of the light-emitting element 9.

[0297] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0298] Table 11 shows element structures of the light-emitting elements 9 and 10 obtained in this way. [Table 11] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2nd electron transport layer Electron injection layer 2nd electrode Light-emitting element 9 ITSO110 nm DBT3P-II:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:DPA2SF:[Ir(tBuppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm Light-emitting element 10 ITSO110 nm DBT3P-II:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:NPB:[Ir(tBuppm)2(acac)](= 0.8:0.2:0.05)40 nm 2mDBTPDBq-II10 nm BPhen20 nm LiF1 nm Al200 nm

[0299] These light-emitting elements were enclosed in a glove box containing a nitrogen atmosphere to prevent their exposure to air. The operating characteristics of these light-emitting elements were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0300] Fig. Figure 38 represents a current density-luminance characteristic curve of the light-emitting elements 9 and 10. Fig. 38 represents the current density (mA / cm²) on the horizontal axis. 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 39 represents a voltage-luminance characteristic curve. Fig. 39 The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 40 represents a luminance-current efficiency characteristic curve. Fig.40 represents the horizontal axis, the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 41 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 41 The horizontal axis represents the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0301] Furthermore, Table 12 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current efficiency (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting elements 9 and 10 at a luminance of approximately 1,000 cd / m² 2 dar. [Table 12] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Luminance (cd / m²) 2 ) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 9 2,9 1,7 (0,43, 0,56) 890 52 56 15 Light-emitting element 10 2,8 1,0 (0,42, 0,57) 820 84 95 23

[0302] Fig. Figure 42 presents emission spectra of the light-emitting elements 9 and 10, obtained by applying a current of 0.1 mA. Fig.Figure 42 shows that the horizontal axis represents the wavelength (nm), and the vertical axis represents the emission intensity (arbitrary unit). As shown in Table 12, the CIE chromaticity coordinates of light-emitting element 9 were (x, y) = (0.43, 0.56) at a luminance of 890 cd / m². 2 , and the CIE chromaticity coordinates of the light-emitting element 10 were (x, y) = (0.42, 0.57) at a luminance of 820 cd / m² 2 The results show that the light-emitting elements 9 and 10 emit a yellow-green light originating from [Ir(tBuppm)2(acac)].

[0303] As shown in Table 12 and Fig. 38, Fig. 39, Fig. 40 to Fig. As can be seen in Figure 41, each of the light-emitting elements 9 and 10 exhibits a high current yield, a high efficiency, and a high external quantum efficiency.

[0304] The light-emitting layer of light-emitting element 9 contains DPA2SF, 2mDBTPDBq-II, and [Ir(tBuppm)2(acac)], as described in Example 10, and the light-emitting layer of light-emitting element 10 contains NPB, 2mDBTPDBq-II, and [Ir(tBuppm)2(acac)], as described in Example 10. As described in Example 10, the emission spectra of the material mixture of 2mDBTPDBq-II and DPA2SF and the material mixture of 2mDBTPDBq-II and NPB show strong overlap with the absorption band in the absorption spectrum of [Ir(tBuppm)2(acac)], which is thought to contribute significantly to light emission. It is believed that the light-emitting elements 9 and 10 exhibit high energy transfer efficiency and external quantum efficiency, as energies are transferred using the overlaps.In particular, the emission spectrum of the material mixture of 2mDBTPDBq-II and NPB exhibits a greater overlap with the absorption band than the emission spectrum of the material mixture of 2mDBTPDBq-II and DPA2SF. Therefore, it is considered that light-emitting element 10 has a higher energy transfer efficiency and external quantum efficiency than light-emitting element 9, since energy is transferred via the greater overlap. Referring to the results of Example 10, it follows that the difference between the energy value of a maximum in the emission spectrum of the host material and the energy value of a maximum in the absorption band on the side of lowest energy in the absorption spectrum of the guest material is preferably 0.3 eV or less.

[0305] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency. [Example 12]

[0306] Example 12 presents examples of a guest material and host materials that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 43A and Fig. 43B.

[0307] The guest material used in this example is [Ir(mppr-Me)2(dpm)]. The host materials also used in this example are the following two types: a mixture of 2mDBTPDBq-II and 4,4',4''-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation: 1'-TNATA) and a mixture of 2-[4-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: DBTBIm-II) and 1'-TNATA. A chemical formula of one of the materials used in this example is shown below. Note that the chemical formulas of the materials used in the examples above are omitted here. (Absorption spectrum)

[0308] Fig. 43A and Fig.Figure 43B shows an ultraviolet visible absorption spectrum (absorption spectrum e) of [Ir(mppr-Me)2(dpm)] in a dichloromethane solution of [Ir(mppr-Me)2(dpm)]. Absorption spectrum measurements were performed at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solution (0.093 mmol / L) in a quartz cuvette. (Emission spectra)

[0309] Fig. 43A and Fig. Figure 43B also presents an emission spectrum (e-1 emission spectrum) of a thin film of a material mixture of 2mDBTPDBq-II and 1'-TNATA and an emission spectrum (e-2 emission spectrum) of a thin film of a material mixture of DBTBIm-II and 1'-TNATA. Fig. 43A the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig.43 B the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0310] The absorption spectrum e in Fig. Figure 43A shows that [Ir(mppr-Me)2(dpm)] has a broad absorption band around 520 nm. This absorption band is thought to contribute significantly to light emission.

[0311] It turns out that each of the maxima of the emission spectra e-1 and e-2 and the absorption band in the absorption spectrum e, which is assumed to contribute significantly to light emission, exhibit strong overlap. In this way, it is shown that a light-emitting element incorporating a light-emitting layer, where the guest material and one of the host materials of this example are used together, has a high energy transfer efficiency, since energy is transferred via the overlap of the emission spectrum of the host material and the absorption spectrum of the guest material. Therefore, it is shown that a light-emitting element with high external quantum efficiency can be achieved.

[0312] Here, the emission spectrum e-2 exhibits a maximum on a shorter wavelength side (higher energy side) than the emission spectrum e-1. The maximum of the emission spectrum e-2 is closer to the absorption band mentioned above than the maximum of the emission spectrum e-1. From the above in Fig. 43A and Fig. From Equation 43B, it follows that the emission spectrum exhibiting the strongest overlap with the absorption band in the absorption spectrum e, which contributes significantly to light emission, is the emission spectrum e-2. Specifically, the difference between the maximum of the absorption band in the absorption spectrum e (located at approximately 520 nm) and the maximum of the emission spectrum e-1 is 0.35 eV, and the difference between the maximum of the absorption band in the absorption spectrum e (located at approximately 520 nm) and the maximum of the emission spectrum e-2 is 0.01 eV.

[0313] The difference between the maxima of the emission spectra e-1 and e-2 is considered to be due to the difference between the LUMO levels of 2mDBTPDBq-II and DBTBIm-II. Specifically, the LUMO level of 2mDBTPDBq-II is -2.95 eV, whereas the LUMO level of DBTBIm-II is -2.52 eV (both values ​​were calculated by CV measurements). It is considered that, since DBTBIm-II has a higher (flatter) LUMO level than 2mDBTPDBq-II, even when DBTBIm-II is mixed with 1'-TNATA, which has a high HOMO level, the wavelength side on which the maximum of the emission spectrum of the composite material is located is not too long (that is, the maximum of the emission spectrum e-2 is located on a shorter wavelength side than the maximum of the emission spectrum e-1).

[0314] From the above, it follows that a light-emitting element containing a material mixture of DBTBIm-II and 1'-TNATA and [Ir(mppr-Me)2(dpm)] exhibits a higher energy transfer efficiency than a light-emitting element containing a material mixture of 2mDBTPDBq-II and 1'-TNATA and [Ir(mppr-Me)2(dpm)], since energy is transferred via the strong overlap of the emission spectrum of the material mixture and the absorption spectrum of the phosphorescent compound. Therefore, it is shown that a light-emitting element with a higher external quantum efficiency can be achieved. [Example 13]

[0315] Example 13 presents a light-emitting element of an embodiment of the present invention with reference to Fig. 2. The materials used in this example are also used in the examples above, and therefore their chemical formulas are omitted here.

[0316] The following describes a method for manufacturing light-emitting elements 11 and 12 of this example. (Light-emitting element 11)

[0317] First, an ITSO film was formed over the glass substrate 1100 by a sputtering process, thus forming the first electrode 1101, which served as the anode. Its thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0318] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0319] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0320] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4 Pa was reduced. Then, BPAFLP and molybdenum(VI) oxide were co-evaporated over the first electrode 1101 to form the hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of BPAFLP to molybdenum oxide was adjusted to 4:2 (= BPAFLP:molybdenum oxide).

[0321] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that the hole transport layer 1112 was formed.

[0322] Furthermore, 2mDBTPDBq-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)] were co-deposited to form the light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to 1'-TNATA and [Ir(mppr-Me)2(dpm)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:1'-TNATA:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 was 20 nm.

[0323] Next, a 2mDBTPDBq-II film with a thickness of 30 nm was formed over the light-emitting layer 1113, thus forming the first electron transport layer 1114a.

[0324] Next, a Bphen film with a thickness of 20 nm was formed over the first electron transport layer 1114a, so that the second electron transport layer 1114b was formed.

[0325] Furthermore, a LiF film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that the electron injection layer 1115 was formed.

[0326] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating the second electrode 1103, which served as the cathode. In this way, the light-emitting element 11 of this example was fabricated. (Light-emitting element 12)

[0327] The light-emitting layer 1113 of the light-emitting element 12 was formed by co-evaporation of DBTBIm-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)]. The weight ratio of DBTBIm-II to 1'-TNATA and [Ir(mppr-Me)2(dpm)] was adjusted to 0.8:0.2:0.05 (= DBTBIm-II:1'-TNATA:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 was 20 nm.

[0328] The first electron transport layer 1114a of the light-emitting element 12 was formed by forming a DBTBIm-II film with a thickness of 30 nm. The layers other than the light-emitting layer 1113 and the first electron transport layer 1114a were formed in the same way as those of the light-emitting element 11.

[0329] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0330] Table 13 shows element structures of the light-emitting elements 11 and 12 obtained in this way. [Table 13] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2. Electron transport layer Electron injection layer 2nd electrode Light-emitting element 11 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:1'-TNATA:[Ir(mppr-Me)2(dpm)](= 0.8:0.2:0.05)20 nm 2mDBTPDBq-II 30 nm BPhen20 nm LiF1 nm Al200 nm Light-emitting element 12 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm DBTBIm-II:1'-TNATA:[Ir(mppr-Me)2(dpm)](=0.8:0.2:0.05)20 nm DBTBIm-II30 nm BPhen20 nm LiF1 nm Al200 nm

[0331] These light-emitting elements were enclosed in a glove box containing a nitrogen atmosphere to prevent their exposure to air. The operating characteristics of these light-emitting elements were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0332] Fig. Figure 44 represents a current density-luminance characteristic curve of the light-emitting elements 11 and 12. Fig. 44 the horizontal axis represents the current density (mA / cm²). 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 45 represents a voltage-luminance characteristic curve. Fig.45 The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 46 represents a luminance-current efficiency characteristic curve. Fig. 46 The horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 47 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 47 The horizontal axis represents the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0333] Furthermore, Table 14 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current yield (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting elements 11 and 12 at a luminance of approximately 860 cd / m² 2 dar. [Table 14] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Luminance (cd / m²) 2 ) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 11 3,1 2,9 (0,53, 0,46) 860 29 30 11 Light-emitting element 12 3,8 1,5 (0,53, 0,46) 860 58 48 21

[0334] Fig. Figure 48 presents emission spectra of the light-emitting elements 11 and 12, obtained by applying a current of 0.1 mA. Fig. Figure 48 shows that the horizontal axis represents the wavelength (nm), and the vertical axis represents the emission intensity (arbitrary unit). As shown in Table 14, the CIE chromaticity coordinates of light-emitting element 11 and light-emitting element 12 were (x, y) = (0.53, 0.46) at a luminance of 860 cd / m². 2 The results show that the light-emitting elements 11 and 12 emit an orange light originating from [Ir(mppr-Me)2(dpm)].

[0335] As shown in Table 14 and Fig. 44, Fig. 45, Fig. 46 to Fig. As can be seen in Figure 47, each of the light-emitting elements 11 and 12 exhibits a high current yield, a high efficiency and a high external quantum efficiency.

[0336] The light-emitting layer of light-emitting element 11 contains 2mDBTPDBq-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)], as described in Example 12, and the light-emitting layer of light-emitting element 12 contains DBTBIm-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)], as described in Example 12. As described in Example 12, the emission spectra of the material mixture of 2mDBTPDBq-II and 1'-TNATA and the material mixture of DBTBIm-II and 1'-TNATA show strong overlap with the absorption band in the absorption spectrum of [Ir(mppr-Me)2(dpm)], which is thought to contribute significantly to light emission. It is believed that the light-emitting elements 11 and 12 exhibit high energy transfer efficiency and external quantum efficiency, as energies are transferred using the overlaps.In particular, the emission spectrum of the material mixture of DBTBIm-II and 1'-TNATA exhibits a greater overlap with the absorption band than the emission spectrum of the material mixture of 2mDBTPDBq-II and 1'-TNATA. Therefore, it is considered that light-emitting element 12 has a higher energy transfer efficiency and external quantum efficiency than light-emitting element 11, since energy is transferred via the greater overlap. Referring to the results of Example 12, it follows that the difference between the energy value of a maximum in the emission spectrum of the host material and the energy value of a maximum in the absorption band on the side of lowest energy in the absorption spectrum of the guest material is preferably 0.3 eV or less.

[0337] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency. [Example 14]

[0338] Example 14 presents examples of a guest material and host materials that may be included in the light-emitting element of an embodiment of the present invention, with reference to Fig. 49A and Fig. 49B.

[0339] The guest material used in this example is [Ir(mppr-Me)2(dpm)]. The host materials also used in this example are the following two types: a mixture of 2mDBTPDBq-II and PCBNBB, and a mixture of 2mDBTPDBq-II and 9-phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP). Chemical formulas of the materials used in this example are shown below. Note that the chemical formulas of the materials used in the examples above are omitted here. (Absorption spectrum)

[0340] Fig. 49A and Fig.Figure 49B shows an ultraviolet visible absorption spectrum (absorption spectrum f) of [Ir(mppr-Me)2(dpm)] in a dichloromethane solution of [Ir(mppr-Me)2(dpm)]. Absorption spectrum measurements were performed at room temperature using a UV / Vis spectrophotometer (type V550, manufactured by JASCO Corporation) with the dichloromethane solution (0.093 mmol / L) in a quartz cuvette. (Emission spectra)

[0341] Fig. 49A and Fig. Figure 49B also presents an emission spectrum (emission spectrum f-1) of a thin film of a material mixture of 2mDBTPDBq-II and PCBNBB and an emission spectrum (emission spectrum f-2) of a thin film of a material mixture of 2mDBTPDBq-II and PCCP. Fig. 49A the horizontal axis represents the wavelength (nm), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig.49 B the horizontal axis represents the energy (eV), and the vertical axes represent the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0342] The absorption spectrum f in Fig. Figure 49A shows that [Ir(mppr-Me)2(dpm)] has a broad absorption band around 500 nm. This absorption band is thought to contribute significantly to light emission.

[0343] It turns out that each of the maxima of the emission spectra f-1 and f-2 and the absorption band in the absorption spectrum f, which is assumed to contribute significantly to light emission, exhibit strong overlap. In this way, it is shown that a light-emitting element incorporating a light-emitting layer, where the guest material and one of the host materials of this example are used together, has a high energy transfer efficiency, since energy is transferred via the overlap of the emission spectrum of the host material and the absorption spectrum of the guest material. Therefore, it is shown that a light-emitting element with high external quantum efficiency can be achieved.

[0344] Example 14 shows that either the material mixture containing the carbazole compound or the composite material containing the aromatic amine compound can be used as the host material. [Example 15]

[0345] Example 15 presents a light-emitting element of an embodiment of the present invention with reference to Fig. 2. The materials used in this example are also used in the examples above, and therefore their chemical formulas are omitted here.

[0346] The following describes a method for manufacturing light-emitting elements 13 and 14 of this example. (Light-emitting element 13)

[0347] First, an ITSO film was formed over the glass substrate 1100 by a sputtering process, thus forming the first electrode 1101, which served as the anode. Its thickness was 110 nm, and the electrode area was 2 mm × 2 mm.

[0348] Next, as a pretreatment to form the light-emitting element above substrate 1100, the surface of the substrate was washed with water, heated at 200 °C for one hour and subjected to a UV ozone treatment for 370 seconds.

[0349] The substrate 1100 was then transferred to a vacuum evaporation apparatus, in which the pressure was set to approximately 10 -4 The Pa had been reduced and subjected to vacuum heating at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for about 30 minutes.

[0350] Next, the substrate 1100, equipped with the first electrode 1101, was attached to a substrate holder in a vacuum evaporation apparatus such that one surface, on which the first electrode 1101 was placed, faced downwards. The pressure in the vacuum evaporation apparatus was set to approximately 10 -4 Pa was reduced. Then, BPAFLP and molybdenum(VI) oxide were co-evaporated over the first electrode 1101 to form the hole injection layer 1111. The thickness of the hole injection layer 1111 was 40 nm, and the weight ratio of BPAFLP to molybdenum oxide was adjusted to 4:2 (= BPAFLP:molybdenum oxide).

[0351] Next, a BPAFLP film with a thickness of 20 nm was formed over the hole injection layer 1111, so that the hole transport layer 1112 was formed.

[0352] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2(dpm)] were co-deposited to form the light-emitting layer 1113 above the hole transport layer 1112. The weight ratio of 2mDBTPDBq-II to PCBNBB and [Ir(mppr-Me)2(dpm)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCBNBB:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 was 20 nm.

[0353] Next, 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2(dpm)] were co-deposited over the light-emitting layer 1113, forming the first electron transport layer 1114a. The weight ratio of 2mDBTPDBq-II to PCBNBB and [Ir(mppr-Me)2(dpm)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCBNBB:[Ir(mppr-Me)2(dpm)]). The thickness of the first electron transport layer 1114a was 40 nm.

[0354] Next, a Bphen film with a thickness of 10 nm was formed over the first electron transport layer 1114a, so that the second electron transport layer 1114b was formed.

[0355] Furthermore, a LiF film with a thickness of 1 nm was formed by vapor deposition over the second electron transport layer 1114b, so that the electron injection layer 1115 was formed.

[0356] Finally, an aluminum foil with a thickness of 200 nm was formed by vapor deposition, creating the second electrode 1103, which served as the cathode. In this way, the light-emitting element 13 of this example was fabricated. (Light-emitting element 14)

[0357] The light-emitting layer 1113 of the light-emitting element 14 was formed by co-evaporation of 2mDBTPDBq-II, 9-phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP), and [Ir(mppr-Me)2(dpm)]. The weight ratio of 2mDBTPDBq-II to PCCP and [Ir(mppr-Me)2(dpm)] was adjusted to 0.8:0.2:0.05 (= 2mDBTPDBq-II:PCCP:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 was 20 nm. The layers other than the light-emitting layer 1113 were formed in the same way as those of the light-emitting element 13.

[0358] It should be noted that in the above vapor deposition process, all vapor deposition was carried out using a resistance heating method.

[0359] Table 15 presents elemental structures of the light-emitting elements 13 and 14 obtained in this way. [Table 15] 1. Electrode Hole injection layer Hole transport layer light-emitting layer 1. Electron transport layer 2nd electron transport layer Electron injection layer 2nd electrode Light-emitting element 13 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-ll:PCBNBB:[Ir(mppr-Me)2(dpm)] (= 0.8:0.2:0.05)20 nm 2mDBTPDBq-ll:PCBNBB:[Ir(mppr-Me)2(dpm)](= 0.8:0.2:0.05)40 nm BPhen10 nm LiF1 nm Al200 nm Light-emitting element 14 ITSO110 nm BPAFLP:MoOx(= 4:2)40 nm BPAFLP20 nm 2mDBTPDBq-II:PCCP:[Ir(mppr-Me)2(dpm)] (= 0.8:0.2:0.05)20 nm 2mDBTPDBq-ll:PCBNBB:[Ir(mppr-Me)2(dpm)](= 0.8:0.2:0.05)40 nm BPhen10 nm LiF1 nm Al200 nm

[0360] These light-emitting elements were enclosed in a glove box containing a nitrogen atmosphere to prevent their exposure to air. The operating characteristics of these light-emitting elements were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0361] Fig. Figure 50 represents a current density-luminance characteristic curve of the light-emitting elements 13 and 14. Fig. 50 represents the current density (mA / cm²) on the horizontal axis. 2 ) represents the luminance (cd / m²), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 51 represents a voltage-luminance characteristic curve. Fig. 51 The horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 52 represents a luminance-current efficiency characteristic curve. Fig.52 represents the horizontal axis, the luminance (cd / m²). 2 ) and the vertical axis represents the current output (cd / A). Fig. Figure 53 represents a characteristic curve of luminance versus external quantum efficiency. Fig. 53 represents the horizontal axis, the luminance (cd / m²). 2 ) represents, and the vertical axis represents the external quantum efficiency (%).

[0362] Furthermore, Table 16 presents the voltage (V) and the current density (mA / cm²). 2 ), the CIE chromaticity coordinates (x, y), the current efficiency (cd / A), the efficiency (Im / W) and the external quantum efficiency (%) of the light-emitting elements 13 and 14 at a luminance of about 1,200 cd / m² 2 dar. [Table 16] Voltage (V) Current density (mA / cm³) 2 ) Color type (x, y) Luminance (cd / m²) 2 ) Power output (cd / A) Efficiency (Im / W) External quantum efficiency (%) Light-emitting element 13 3,0 1,7 (0,54, 0,45) 1.200 67 70 24 Light-emitting element 14 3,0 1,7 (0,54, 0,46) 1.200 69 72 24

[0363] Fig. Figure 54 presents emission spectra of the light-emitting elements 13 and 14, obtained by applying a current of 0.1 mA. Fig.Figure 54 represents the horizontal axis as the wavelength (nm), and the vertical axis as the emission intensity (arbitrary unit). As shown in Table 16, the CIE chromaticity coordinates of the light-emitting element 13 were (x, y) = (0.54, 0.45) at a luminance of 1200 cd / m². 2 , and the CIE chromaticity coordinates of the light-emitting element 14 were (x, y) = (0.54, 0.46) at a luminance of 1,200 cd / m² 2 The results show that the light-emitting elements 13 and 14 emit an orange light originating from [Ir(mppr-Me)2(dpm)].

[0364] As shown in Table 16 and Fig. 50, Fig. 51, Fig. 52 to Fig. As can be seen in Figure 53, each of the light-emitting elements 13 and 14 exhibits a high current yield, a high efficiency and a high external quantum efficiency.

[0365] The light-emitting layer of the light-emitting element 13 comprises 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2(dpm)], as described in Example 14, and the light-emitting layer of the light-emitting element 14 comprises 2mDBTPDBq-II, PCCP, and [Ir(mppr-Me)2(dpm)], as described in Example 14. As described in Example 14, the emission spectra of the material mixture of 2mDBTPDBq-II and PCBNBB and the material mixture of 2mDBTPDBq-II and PCCP show strong overlap with the absorption band in the absorption spectrum of [Ir(mppr-Me)2(dpm)], which is thought to contribute significantly to light emission. The light-emitting elements 13 and 14 are considered to have high energy transfer efficiency and external quantum efficiency, as energies are transferred using the overlaps.

[0366] Example 15 suggests that if the material mixture containing the carbazole compound (PCCP) is used as the host material in the light-emitting layer instead of the material mixture containing the aromatic amine compound (PCBNBB), a light-emitting element with high external quantum efficiency can also be achieved.

[0367] The above results show that the application of an embodiment of the present invention makes it possible to achieve a light-emitting element with a high external quantum efficiency. (Reference example 1)

[0368] The following is a synthesis example for a metal-organic complex (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (another name: Bis[2-(6-phenyl-4-pyrimidinyl-ĸN3)phenyl-ĸC](2,4-pentanedionato-ĸ 2O,O')iridium(III)) (abbreviation: [Ir(dppm)2(acac)]) is shown, which is used in the examples above. The structure of [Ir(dppm)2(acac)] is shown below. 〈Step 1: Synthesis of 4,6-Diphenylpyrimidine (abbreviation: Hdppm〉〉

[0369] First, 5.02 g of 4,6-dichloropyrimidine, 8.29 g of phenylboronic 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 argon. This reaction vessel was heated for 60 minutes by microwave irradiation (2.45 GHz, 100 W). Then, 2.08 g of phenylboronic acid, 1.79 g of sodium carbonate, 0.070 g of Pd(PPh3)2Cl2, 5 ml of water, and 5 ml of acetonitrile were added to the flask, and the mixture was again heated for 60 minutes by microwave irradiation (2.45 GHz, 100 W). Water was then added to this solution, and an organic layer was extracted with dichloromethane. The resulting extract solution was washed with water and dried with magnesium sulfate. After drying, the solution was filtered.The solvent of this solution was distilled off, and the resulting residue was then purified by silica gel column chromatography with dichloromethane as the mobile phase, affording a pyrimidine derivative Hdppm (yellow-white powder, yield 38%). It should be noted that a microwave synthesis system (Discover, manufactured by CEM Corporation) was used for the microwave irradiation. A synthesis scheme (a-1) of step 1 is shown below. 〈Step 2: Synthesis of di-µ-chlorobis[bis(4,6-diphenylpyrimidinato)iridium(III)] (abbreviation: [Ir(dppm)2Cl]2))

[0370] Next, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.10 g of the Hdppm obtained in step 1, and 0.69 g of iridium chloride hydrate (IrCl3·H2O) were placed in 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 to induce a reaction. The solvent was distilled off, and the resulting residue was subsequently filtered and washed with ethanol to generate a dinuclear complex [Ir(dppm)2Cl]2 (reddish-brown powder, yield 88%). A synthesis scheme (a-2) of step 2 is presented below. 〈Step 3: Synthesis of (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]〉

[0371] Furthermore, 40 ml of 2-ethoxyethanol, 1.44 g of the [Ir(dppm)₂Cl]₂ obtained in step 2, 0.30 g of acetylacetone, and 1.07 g of sodium carbonate were placed in a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 120 W) for 60 minutes to induce a reaction. The solvent was distilled off, the resulting residue was dissolved in dichloromethane, and filtration was performed to remove insoluble substances. The filtrate was washed with water and then with saturated salt solution and dried with magnesium sulfate. After drying, the solution was filtered. The solvent of this solution was distilled off, and the residue was then purified by silica gel column chromatography using dichloromethane and ethyl acetate as mobile phases in a volume ratio of 50:1.A recrystallization was then carried out with a solvent mixture of dichloromethane and hexane, yielding an orange powder as the target substance (yield 32%). A synthesis scheme (a-3) of step 3 is presented below.

[0372] The following is an analysis result from nuclear magnetic resonance spectrometry ( 1 The results of the ¹H NMR analysis of the orange powder obtained in step 3 were described. These results showed that the organometallic complex [Ir(dppm)2(acac)] was obtained.

[0373] 1 H NMR. δ (CDCl3): 1.83 (s, 6H), 5.29 (s, 1H), 6.48 (d, 2H), 6.80 (t, 2H), 6.90 (t, 2H), 7.55-7.63 (m, 6H), 7.77 (d, 2H), 8.17 (s, 2H), 8.24 (d, 4H), 9.17 (s, 2H). (Reference example 2)

[0374] The following is a synthesis example for a metal-organic complex (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (another name: Bis[2-(6-methyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2 O,O')iridium(III)) (abbreviation: [Ir(mppm)2(acac)]) is shown, which is used in the examples above. The structure of [Ir(mppm)2(acac)] is shown below. (Step 1: Synthesis of 4-methyl-6-phenylpyrimidine (abbreviation: Hmppm))

[0375] First, 4.90 g of 4-chloro-6-methylpyrimidine, 4.80 g of phenylboronic acid, 4.03 g of sodium carbonate, 0.16 g of bis(triphenylphosphine)palladium(II) dichloride (abbreviation: Pd(PPh3)2Cl2), 20 ml of water, and 10 ml of acetonitrile were placed in a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with argon. This reaction vessel was heated for 60 minutes by microwave irradiation (2.45 GHz, 100 W). Then, 2.28 g of phenylboronic acid, 2.02 g of sodium carbonate, 0.082 g of Pd(PPh3)2Cl2, 5 ml of water, and 10 ml of acetonitrile were added to the flask, and the mixture was heated again for 60 minutes by microwave irradiation (2.45 GHz, 100 W). Water was then added to this solution, and an extraction with dichloromethane was carried out.The obtained extract solution was washed with a saturated aqueous sodium carbonate solution, water, and subsequently with 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 then purified by silica gel column chromatography using dichloromethane and ethyl acetate as mobile phases in a volume ratio of 9:1, yielding the pyrimidine derivative Hmppm as the target compound (an orange, oily substance, yield 46%). It should be noted that microwave irradiation was performed using a microwave synthesis system (Discover, manufactured by CEM Corporation). A synthesis scheme (b-1) of step 1 is presented below. 〈Step 2: Synthesis of Di-µ-chlorobis[bis(6-methyl-4-phenylpyrimidinato)iridium(III)] (abbreviation: [Ir(mppm)2Cl]2)〉

[0376] Next, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.51 g of the Hmppm obtained in step 1, and 1.26 g of iridium chloride hydrate (IrCl3·H2O) were placed in 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 to induce a reaction. The solvent was distilled off, and the resulting residue was then washed with ethanol and filtered to obtain a dinuclear complex [Ir(mppm)2Cl]2 (dark green powder, yield 77%). A synthesis scheme (b-2) of step 2 is presented below. 〈Step 3: Synthesis of (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)])〉

[0377] Furthermore, 40 ml of 2-ethoxyethanol, 1.84 g of the dinuclear complex [Ir(mppm)2Cl]2 obtained in step 2, 0.48 g of acetylacetone, and 1.73 g of sodium carbonate were placed in 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 to induce a reaction. The solvent was distilled off, the resulting residue was dissolved in dichloromethane, and filtration was performed to remove insoluble substances. The filtrate was washed with water and then with saturated salt solution and dried with magnesium sulfate. After drying, the solution was filtered. The solvent of this solution was distilled off, and the residue was then purified by silica gel column chromatography using dichloromethane and ethyl acetate as mobile phases in a volume ratio of 4:1.Subsequently, recrystallization was carried out with a solvent mixture of dichloromethane and hexane, yielding a yellow powder as the target substance (yield 22%). A synthesis scheme (b-3) of step 3 is presented below.

[0378] The following is an analysis result from nuclear magnetic resonance spectrometry ( 1 The results of the ¹H NMR analysis of the yellow powder obtained in step 3 were described. These results showed that the organometallic complex [Ir(mppm)2(acac)] was obtained.

[0379] 1 H NMR. δ (CDCl3): 1.78 (s, 6H), 2.81 (s, 6H), 5.24 (s, 1H), 6.37 (d, 2H), 6.77 (t, 2H), 6.85 (t, 2H), 7.61-7.63 (m, 4H), 8.97 (s, 2H). (Reference example 3)

[0380] The following is a synthesis example for a metal-organic complex (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (other name: Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ2 O,O')iridium(III)) (abbreviation: [Ir(tBuppm)2(acac)]) is shown, which is used in the examples above. The structure of [Ir(tBuppm)2(acac)] is shown below.

[0381] 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 to allow the reacted solution to reflux for 5 hours. Afterward, 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 saturated salt solution and dried with magnesium sulfate. After drying, the solution was filtered. The solvent was distilled off, and the residue was then 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 (c-1) of step 1 is shown below. 〈Step 2: Synthesis of di-µ-chlorobis[bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)] (abbreviation: [Ir(tBuppm)2Cl]2)〉

[0382] Next, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.49 g of the HtBuppm obtained in step 1, and 1.04 g of iridium chloride hydrate (IrCl3·H2O) were placed in 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 to induce a reaction. The solvent was distilled off, and the resulting residue was then filtered and washed with ethanol to give a dinuclear complex [Ir(tBuppm)2Cl]2 (yellow-green powder, yield 73%). A synthesis scheme (c-2) of step 2 is presented below. 〈Step 3: Synthesis of (Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)])〉

[0383] 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 placed in 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 to induce a 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 in which Celit (manufactured by Wako Pure Chemical Industries, Ltd., catalog no. 531-16855), aluminum oxide, and Celit were stacked in that order.The solvent was distilled off, and the resulting solid was recrystallized with a solvent mixture of dichloromethane and hexane to obtain the target substance as a yellow powder (yield 68%). A synthesis scheme (c-3) of step 3 is shown below.

[0384] The following is an analysis result from nuclear magnetic resonance spectrometry ( 1 The results of the ¹H NMR analysis of the yellow powder obtained in step 3 were described. These results showed that the organometallic complex [Ir(tBuppm)2(acac)] was obtained.

[0385] 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 4)

[0386] The following describes a method for synthesizing 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), which is used in examples. (Synthesis of 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II)〉

[0387] A synthesis scheme (d-1) of 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) is presented below.

[0388] Into a 2-liter three-necked flask, 5.3 g (20 mmol) of 2-chlorodibenzo[f,h]quinoxaline, 6.1 g (20 mmol) of 3-(dibenzothiophen-4-yl)phenylboronic acid, 460 mg (0.4 mmol) of tetrakis(triphenylphosphine)palladium(0), 300 mL of toluene, 20 mL of ethanol, and 20 mL of an aqueous potassium carbonate solution (2M) were placed. The mixture was degassed by stirring under reduced pressure, and the air in the three-necked flask was replaced with nitrogen. This mixture was stirred under a nitrogen stream at 100 °C for 7.5 hours. After cooling to room temperature, the mixture was filtered to obtain a white residue. The residue was washed with water and ethanol in that order and then dried. The recovered solid was dissolved in approximately 600 ml of hot toluene, followed by filtering through Celit and Florisil, resulting in a clear, colorless filtrate.The obtained filtrate was concentrated and purified by silica gel column chromatography using approximately 700 ml of silica gel. Hot toluene was used as the mobile phase. Acetone and ethanol were added to the resulting solid, followed by ultrasonic irradiation. The resulting suspended solid was then collected by filtration and dried, yielding 7.85 g of a white powder in an 80% yield.

[0389] The target compound described above was relatively soluble in hot toluene but was likely to precipitate upon cooling. Furthermore, it was poorly soluble in other organic solvents such as acetone and ethanol. Consequently, exploiting these varying degrees of solubility resulted in a high-yield synthesis using a simple procedure like the one described above. After the reaction was complete, the mixture was cooled back to room temperature, and the precipitated solid was collected by filtration, readily removing most impurities. Additionally, the target compound, which would likely precipitate, could be easily purified by column chromatography using hot toluene as the mobile phase.

[0390] 4.0 g of the recovered white powder were purified by train sublimation. During purification, the white powder was heated at 300 °C under a pressure of 5.0 Pa with an argon gas flow rate of 5 ml / min. After purification, the target substance was recovered in 88% yield as 3.5 g of white powder.

[0391] A nuclear magnetic resonance spectrometry ( 1 H NMR) identified this compound as the target substance 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II).

[0392] 1 H-NMR data of the recovered substance are presented below.

[0393] 1 H NMR (CDCl3, 300 MHz): δ (ppm) = 7.45-7.52 (m, 2H), 7.59-7.65 (m, 2H), 7.71-7.91 (m, 7H), 8.20-8.25 (m, 2H), 8.41 (d, J = 7.8 Hz, 1H), 8.65 (d, J = 7.5 Hz, 2H), 8.77-8.78 (m, 1H), 9.23 (dd, J = 7.2 Hz, 1.5 Hz, 1H), 9.42 (dd, J = 7.8 Hz, 1.5 Hz, 1H), 9.48 (s, 1H). Explanation of reference symbols 102 EL layer, 103 first electrode, 108 second electrode, 701 Hole injection layer, 702 Hole transport layer, 703 Light-emitting layer, 704 Electron transport layer, 705 Electron injection layer, 706 Electron injection buffer layer, 707 Electron relay layer, 708 Composite material layer, 800 first EL layer, 801 second EL layer, 803 Charge generation layer, 1100 substrate, 1101 first electrode, 1103 second electrode, 1111 Hole injection layer, 1112 Hole transport layer, 1113 Light-emitting layer, 1114a first electron transport layer, 1114b second electron transport layer, 1115 Electron injection layer.

Claims

[1] Light-emitting element comprising: a first electrode (103); a light-emitting layer (703) above the first electrode (103), wherein the light-emitting layer (703) comprises a guest material and a host material; and a second electrode (108) above the light-emitting layer (703), where a fluorescence spectrum of the host material and a phosphorescence spectrum of the host material overlap the absorption band on the longest wavelength side (the side of lowest energy) in the absorption spectrum of the guest material, wherein the difference between the energy value of the maximum of the fluorescence spectrum of the host material and the energy value of the maximum of the absorption band on the side of the lowest energy in the absorption spectrum of the guest material, wherein this maximum has an absorption wavelength corresponding to a direct transition from the singlet ground state to the lowest excited triplet state of the guest material, is 0.2 eV or less, wherein the host material is a mixture of a heterocyclic compound and an aromatic amine compound or carbazole compound, and where the level of a triplet excitation energy of the host material is higher than the level of a triplet excitation energy of the guest material. [2] Light-emitting element comprising: a first electrode (103); a light-emitting layer (703) above the first electrode (103), wherein the light-emitting layer (703) comprises a guest material and a host material; and a second electrode (108) above the light-emitting layer (703), where a fluorescence spectrum of the host material and a phosphorescence spectrum of the host material overlap the absorption band on the longest wavelength side (the side of lowest energy) in the absorption spectrum of the guest material, wherein the difference between the energy value of the maximum of the fluorescence spectrum of the host material and the energy value of the maximum of the absorption band on the side of the lowest energy in the absorption spectrum of the guest material, wherein this maximum has an absorption wavelength corresponding to a direct transition from the singlet ground state to the lowest excited triplet state of the guest material, is 0.1 eV or less, wherein the host material is a mixture of a heterocyclic compound and an aromatic amine compound or carbazole compound, and where the level of a triplet excitation energy of the host material is higher than the level of a triplet excitation energy of the guest material. [3] Light-emitting element according to claim 1 or 2, wherein the absorption band includes absorption based on a triplet MLCT transition. [4] Light-emitting element according to claim 1 or 2, wherein the guest material is a metal-organic complex. [5] Light-emitting element according to claim 1 or 2, wherein the guest material is an iridium complex. [6] Light-emitting element according to claim 1 or 2, wherein a molar absorption coefficient of the absorption band at the longest wavelength side in the absorption spectrum 5000 M - 1 ·cm-1 or more. [7] Light-emitting element according to claim 1 or 2, wherein the carbazole compound comprises a carbazol-3-yl group. [8] Light-emitting element according to claim 1 or 2, wherein the carbazole compound comprises a first carbazole ring and a second carbazole ring, and where the first carbazole ring is connected to the second carbazole ring at the 3 position. [9] Light-emitting element according to claim 1 or 2, wherein the carbazole compound comprises two carbazole rings. [10] Electronic device comprising the light-emitting element according to claim 1 or 2. [11] Lighting device comprising the light-emitting element according to claim 1 or 2.

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