Light-emitting element, light-emitting device, lighting device, and electronic device

Abstract

To provide a light-emitting element having high external quantum efficiency, and a light-emitting element having a long lifetime.SOLUTION: A light-emitting element is provided which includes a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, in which a combination of the first organic compound and the second organic compound forms an exciplex (excited complex). The light-emitting element transfers energy by utilizing an overlap between the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound and thus has high energy transfer efficiency. Therefore, a light-emitting element having high external quantum efficiency can be obtained.SELECTED DRAWING: Figure 25

Description

[Technical Field]

[0001] Organic electroluminescence (EL) phenomenon The present invention relates to a light-emitting device (hereinafter also referred to as an organic EL device) utilizing the above. [Background technology]

[0002] Research and development of organic EL elements is actively underway. The basic structure of an organic EL element is a pair of A layer containing a light-emitting organic compound (hereinafter referred to as a light-emitting layer) is sandwiched between electrodes. Lightweight type, high-speed response to input signals, and low DC voltage drive are possible. Therefore, it is attracting attention as a next-generation flat panel display element. Displays using these light-emitting elements have the advantages of excellent contrast and image quality, as well as a wide viewing angle. Furthermore, since organic EL elements are surface light sources, they can be used as backlights for LCD displays. Applications as a light source for lights and illumination are also being considered.

[0003] The light-emitting mechanism of organic EL elements is a carrier injection type. In other words, the light-emitting layer is sandwiched between electrodes. By applying a voltage, electrons and holes injected from the electrode recombine and The luminescent material is excited and emits light when the excited state returns to the ground state. The types of states include the singlet excited state (S * ) and triplet excited states (T * ) is possible. The statistical generation rate of light-emitting elements is S * :T * =1:3 are.

[0004] The ground state of luminescent organic compounds is usually a singlet state. Therefore, the singlet excited state (S * ) is called fluorescence because it is an electron transition between atoms of the same spin multiplicity. , triplet excited state (T * ) is an electron transition between different spin multiplicities, Here, a compound that emits fluorescence (hereinafter referred to as a fluorescent compound) emits light at room temperature. Therefore, phosphorescence is not observed and only fluorescence is observed. The internal quantum efficiency (the ratio of photons generated to injected carriers) of a light-emitting device The theoretical limit is S * :T * It is said to be 25% based on the ratio = 1:3.

[0005] On the other hand, if a compound that emits phosphorescence (hereinafter referred to as a phosphorescent compound) is used, the internal quantum efficiency can be increased to 1 In other words, it is possible to obtain a higher luminous efficiency than fluorescent compounds. For this reason, in order to realize a highly efficient light-emitting device, phosphorescent compounds are used. In recent years, the development of light-emitting devices using phosphorescent compounds has been actively pursued. Due to the high phosphorescence quantum yield of iridium, organometallic complexes with iridium as the central metal have attracted attention. For example, Patent Document 1 discloses that an organometallic complex having iridium as the central metal is a phosphorescent material. and is disclosed as such.

[0006] When the light-emitting layer of the light-emitting element is formed using the above-mentioned phosphorescent compound, the concentration quenching of the phosphorescent compound is To suppress quenching by light and triplet-triplet annihilation, the compound is placed in a matrix of other compounds. In most cases, the phosphorescent compound is dispersed in a matrix. The compound is the host material, and the compound dispersed in the matrix, such as a phosphorescent compound, is the guest material. It is called a fee. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 00 / 70655 Brochure Summary of the Invention [Problem to be solved by the invention]

[0008] However, the light extraction efficiency of organic EL elements is generally said to be around 20% to 30%. Therefore, when considering the absorption of light by the reflective electrode and transparent electrode, it is recommended to use a phosphorescent compound. The limit of external quantum efficiency of light-emitting devices is thought to be about 25%.

[0009] In view of the above, an object of one embodiment of the present invention is to provide a light-emitting element with high external quantum efficiency. Another object of one embodiment of the present invention is to provide a light-emitting element with a long lifetime. [Means for solving the problem]

[0010] One aspect of the present invention is a light-emitting device comprising a phosphorescent compound, a first organic compound, and a second organic compound. The layer is disposed between a pair of electrodes, and a first organic compound and a second organic compound form an exciplex. The light-emitting element is a combination of these elements.

[0011] Another embodiment of the present invention is a light-emitting device including a phosphorescent compound, a first organic compound, and a second organic compound. The light-emitting layer is disposed between a pair of electrodes and includes a first organic compound and a second organic compound. The exciplex acts on the phosphorescent compound, causing the phosphorescent compound to emit phosphorescence. It is a light-emitting element that emits light.

[0012] Another embodiment of the present invention is a light-emitting device including a phosphorescent compound, a first organic compound, and a second organic compound. The light-emitting layer is disposed between a pair of electrodes, and an exciplex is formed from the singlet exciton of the first organic compound. It is a light emitting element.

[0013] Another embodiment of the present invention is a light-emitting device including a phosphorescent compound, a first organic compound, and a second organic compound. The light-emitting layer is disposed between a pair of electrodes and includes an anion of a first organic compound and a cation of a second organic compound. This is a light-emitting element in which an exciplex is formed from thione.

[0014] In the light-emitting element, the excitation energy of the exciplex is transferred to the phosphorescent compound, Preferably, the compound is phosphorescent.

[0015] In the light-emitting device, at least one of the first organic compound and the second organic compound is fluorescent. It is preferable that the compound is a carboxylic acid compound.

[0016] In the above light-emitting element, the phosphorescent compound is preferably an organometallic complex.

[0017] The light-emitting element of one embodiment of the present invention can be applied to light-emitting devices, electronic devices, and lighting devices. do. [Effects of the Invention]

[0018] According to one embodiment of the present invention, a light-emitting element with high external quantum efficiency can be provided. In one embodiment, a light-emitting element with a long lifetime can be provided. [Brief explanation of the drawings]

[0019] [Figure 1] 3A and 3B are diagrams showing absorption spectra and emission spectra according to Example 1. FIG. [Figure 2] 10A and 10B are diagrams showing absorption spectra and emission spectra according to Example 2. [Figure 3] FIG. 10 is a graph showing current density-luminance characteristics of the light-emitting element of Example 3. [Figure 4] FIG. 10 is a graph showing voltage-luminance characteristics of the light-emitting element of Example 3. [Figure 5] FIG. 10 shows luminance-current efficiency characteristics of the light-emitting element of Example 3. [Figure 6] FIG. 10 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 3. [Figure 7] FIG. 10 shows an emission spectrum of the light-emitting element of Example 3. [Figure 8] FIG. 10 shows the results of a reliability test of the light-emitting element of Example 3. [Figure 9] FIG. 10 is a graph showing current density-luminance characteristics of the light-emitting element of Example 4. [Figure 10] FIG. 10 is a graph showing voltage-luminance characteristics of the light-emitting element of Example 4. [Figure 11] FIG. 10 shows luminance-current efficiency characteristics of the light-emitting element of Example 4. [Figure 12] FIG. 10 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 4. [Figure 13] FIG. 10 shows an emission spectrum of the light-emitting element of Example 4. [Figure 14] FIG. 10 shows the results of a reliability test of the light-emitting element of Example 4. [Figure 15] 1A and 1B are diagrams showing the structure of a light-emitting element according to an embodiment; [Figure 16] 1A and 1B illustrate light-emitting elements of one embodiment of the present invention. [Figure 17] FIG. 1 illustrates energy levels of an exciplex used in one embodiment of the present invention. [Figure 18] 10A and 10B are diagrams showing absorption spectra and emission spectra according to Example 5. [Figure 19] FIG. 10 is a graph showing current density-luminance characteristics of the light-emitting element of Example 6. [Figure 20] FIG. 10 shows voltage-luminance characteristics of the light-emitting element of Example 6. [Figure 21] FIG. 10 shows luminance-current efficiency characteristics of the light-emitting element of Example 6. [Figure 22] FIG. 10 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 6. [Figure 23] FIG. 10 shows an emission spectrum of the light-emitting element of Example 6. [Figure 24] FIG. 10 shows the results of a reliability test of the light-emitting element of Example 6. [Figure 25] 1A and 1B illustrate a concept of one embodiment of the present invention. [Figure 26] FIG. 10 shows an absorption spectrum and an emission spectrum according to Example 7. [Figure 27] FIG. 10 is a graph showing current density-luminance characteristics of the light-emitting element of Example 8. [Figure 28] FIG. 10 shows voltage-luminance characteristics of the light-emitting element of Example 8. [Figure 29] FIG. 10 shows luminance-current efficiency characteristics of the light-emitting element of Example 8. [Figure 30] FIG. 10 is a graph showing the luminance-external quantum efficiency characteristics of the light-emitting element of Example 8. [Figure 31] FIG. 10 shows an emission spectrum of the light-emitting element of Example 8. [Figure 32] FIG. 10 shows the absorption spectrum and the emission spectrum according to Example 9. [Figure 33] FIG. 13 shows current density-luminance characteristics of the light-emitting element of Example 10. [Figure 34] FIG. 16 shows voltage-luminance characteristics of the light-emitting element of Example 10. [Figure 35] FIG. 13 shows luminance-current efficiency characteristics of the light-emitting element of Example 10. [Figure 36] FIG. 13 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 10. [Figure 37] FIG. 13 shows an emission spectrum of the light-emitting element of Example 10. [Figure 38] FIG. 13 shows the results of a reliability test of the light-emitting element of Example 10. [Figure 39] FIG. 11 shows the absorption spectrum and the emission spectrum according to Example 11. [Figure 40] FIG. 16 shows current density-luminance characteristics of the light-emitting element of Example 12. [Figure 41] FIG. 16 shows voltage-luminance characteristics of the light-emitting element of Example 12. [Figure 42] FIG. 16 shows luminance-current efficiency characteristics of the light-emitting element of Example 12. [Figure 43] FIG. 16 shows luminance-external quantum efficiency characteristics of the light-emitting element of Example 12. [Figure 44] FIG. 16 shows an emission spectrum of the light-emitting element of Example 12. [Figure 45] FIG. 16 shows the results of a reliability test of the light-emitting element of Example 12. [Figure 46] FIG. 13 shows the absorption spectrum and the emission spectrum according to Example 13. [Figure 47] FIG. 16 shows current density-luminance characteristics of the light-emitting element of Example 14. [Figure 48] FIG. 16 shows voltage-luminance characteristics of the light-emitting element of Example 14. [Figure 49] FIG. 16 shows luminance-current efficiency characteristics of the light-emitting element of Example 14. [Figure 50] FIG. 16 shows the luminance-external quantum efficiency characteristics of the light-emitting element of Example 14. [Figure 51] FIG. 16 shows an emission spectrum of the light-emitting element of Example 14. [Figure 52] FIG. 16 shows the absorption spectrum and the emission spectrum according to Example 15. [Figure 53] FIG. 16 shows current density-luminance characteristics of the light-emitting element of Example 16. [Figure 54] FIG. 16 shows voltage-luminance characteristics of the light-emitting element of Example 16. [Figure 55] FIG. 16 shows luminance-current efficiency characteristics of the light-emitting element of Example 16. [Figure 56] FIG. 16 shows luminance-external quantum efficiency characteristics of the light-emitting element of Example 16. [Figure 57] FIG. 16 shows an emission spectrum of the light-emitting element of Example 16. [Figure 58] FIG. 11 shows the absorption spectrum and the emission spectrum according to Example 17. [Figure 59] FIG. 19 shows current density-luminance characteristics of the light-emitting element of Example 18. [Figure 60] FIG. 19 shows voltage-luminance characteristics of the light-emitting element of Example 18. [Figure 61] FIG. 19 shows luminance-current efficiency characteristics of the light-emitting element of Example 18. [Figure 62]FIG. 19 shows the luminance-external quantum efficiency characteristics of the light-emitting element of Example 18. [Figure 63] FIG. 19 shows an emission spectrum of the light-emitting element of Example 18. [Figure 64] FIG. 10 shows calculation results according to one embodiment of the present invention. [Figure 65] FIG. 10 shows calculation results according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description. The present invention is not limited to the above embodiments, and various changes and modifications may be made in the form and details thereof without departing from the spirit and scope of the present invention. It will be readily understood by those skilled in the art that the present invention can be achieved by the following embodiments. It should not be construed as being limited to the contents of the description. The same reference numerals are used in different drawings to denote the same parts or parts having similar functions. A repeated explanation will be omitted.

[0021] (Embodiment 1) In this embodiment, a light-emitting element of one embodiment of the present invention will be described.

[0022] The light-emitting element of this embodiment mode includes a guest material which is a light-emitting substance, a first organic compound, and a second organic compound. The light-emitting layer contains an organic compound. Specifically, a phosphorescent compound is used as a guest material. In this specification, the first organic compound and the second organic compound contained in the light-emitting layer are The material that is contained in the majority of the mixture is called the host material.

[0023] By dispersing the guest material in the host material, crystallization of the light-emitting layer is suppressed. In addition, concentration quenching caused by a high concentration of the guest material can be suppressed, and the light-emitting element can be The luminous efficiency can be increased.

[0024] In this embodiment, the first organic compound and the second organic compound are each triple-layered. The first excitation energy level (T1 level) is preferably higher than the T1 level of the guest material. The T1 level of the first organic compound (or the second organic compound) is higher than the T1 level of the guest material. If the triplet excitation energy of the guest material that contributes to light emission is low, the triplet excitation energy of the first organic compound (or This is because the second organic compound is quenched, resulting in a decrease in luminous efficiency.

[0025] <Elemental process of luminescence> First, we will explain the general elementary process of light emission in a light-emitting device that uses a phosphorescent compound as a guest material. explain.

[0026] (1) When electrons and holes recombine in the guest molecule, the guest molecule enters an excited state. (direct recombination process). (1-1) When the excited state of the guest molecule is a triplet excited state The guest molecule emits phosphorescence. (1-2) When the excited state of the guest molecule is a singlet excited state The guest molecule in the singlet excited state undergoes intersystem crossing to the triplet excited state, emitting phosphorescence.

[0027] In other words, in the direct recombination process (1) above, the intersystem crossing efficiency of the guest molecule and the phosphorescence If the quantum yield is high, high luminous efficiency can be obtained. The T1 level of the host molecule is preferably higher than the T1 level of the guest molecule.

[0028] (2) When electrons and holes recombine in the host molecule, the host molecule enters an excited state. (energy transfer process). (2-1) When the excited state of the host molecule is a triplet excited state If the T1 level of the host molecule is higher than the T1 level of the guest molecule, the host molecule The excitation energy is transferred to the guest molecule, and the guest molecule enters a triplet excited state. The guest molecule emits phosphorescence. Although energy transfer to the S1 level of the guest molecule is formally possible, in most cases the energy transfer is to the S1 level of the guest molecule. is located on the higher energy side than the T1 level of the host molecule, and is the main energy transfer pathway. Since it is difficult to achieve this level, we will not go into detail here. (2-2) When the excited state of the host molecule is a singlet excited state If the S1 level of the host molecule is higher than the S1 and T1 levels of the guest molecule, the host Excitation energy is transferred from the molecule to the guest molecule, and the guest molecule enters a singlet excited state or a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. The guest molecule in this state undergoes intersystem crossing to a triplet excited state and emits phosphorescence.

[0029] In other words, in the energy transfer process (2) above, the triplet excitation energy of the host molecule It is important to transfer both the singlet and singlet excitation energy to the guest molecule efficiently. This becomes:

[0030] Considering this energy transfer process, excitation energy is transferred from the host molecule to the guest molecule. Before this happens, the host molecule itself is deactivated, releasing its excitation energy as light or heat. Here, the present inventors have investigated whether the host molecule is in a singlet excited state. In the triplet excited state (above (2-2)), the In all cases, energy transfer to the guest molecule, which is a phosphorescent compound, is difficult, resulting in low luminous efficiency. The reasons for this are as follows: This was derived by considering the energy transfer process.

[0031] <Energy transfer process> The energy transfer process between molecules is described in detail below.

[0032] First, the following two mechanisms have been proposed for intermolecular energy transfer: The molecule that provides the excitation energy is the host molecule, and the molecule that receives the excitation energy is the is referred to as the guest molecule.

[0033] <Förster mechanism (dipole-dipole interaction)> The Förster mechanism does not require direct contact between molecules for energy transfer. Energy transfer occurs through the resonance phenomenon of dipole vibration between the molecule and the guest molecule. The host molecule transfers energy to the guest molecule through the vibrational resonance phenomenon, and the host molecule The guest molecule enters the excited state. The rate constant of the Förster mechanism is k h * →g of This is shown in equation (1).

[0034]

number

[0035] In formula (1), ν represents the frequency, and f' h (ν) is the normalized Emission spectrum (fluorescence spectrum when discussing energy transfer from singlet excited states, When discussing energy transfer from triplet excited states, it represents the phosphorescence spectrum, and ε g (ν ) represents the molar extinction coefficient of the guest molecule, N represents Avogadro's number, and n represents the refractive index of the medium. represents the rate of excitation, R represents the intermolecular distance between the host molecule and the guest molecule, and τ represents the measured excitation state. represents the lifetime of the state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, and φ represents the luminescence quantum yield (single When discussing energy transfer from single excited states, the fluorescence quantum yield is used, and when discussing energy transfer from triplet excited states, the fluorescence quantum yield is used. When discussing energy transfer, it represents the phosphorescence quantum yield, and K 2 is the ratio of the host molecule and the guest molecule This is a coefficient (0 to 4) that represents the orientation of the transition dipole moment. In the case of random orientation, K 2 =2 / 3.

[0036] Dexter mechanism (electron exchange interaction) In the Dexter mechanism, the host and guest molecules are close to the effective contact distance where orbital overlap occurs. Based on this, energy is transferred through the exchange of electrons of the excited host molecule and the ground state guest molecule. The rate constant of the Dexter mechanism, k h * →g is shown in equation (2).

[0037]

number

[0038] In equation (2), h is Planck's constant, and K is a constant with the dimension of energy. where ν represents the frequency and f' h (ν) is the normalized emission spectrum of the host molecule (When discussing energy transfer from the singlet excited state, the fluorescence spectrum, triplet excited state represents the phosphorescence spectrum when discussing energy transfer from g (ν) is a guest represents the normalized absorption spectrum of the molecule, L represents the effective molecular radius, and R represents the effective molecular radius of the host molecule. Represents the intermolecular distance between the child and guest molecules.

[0039] Here, the energy transfer efficiency from the host molecule to the guest molecule Φ ET is expressed by equation (3). It is thought that r The emission process of the host molecule (energy transfer from the singlet excited state) The rate of fluorescence is used when discussing the energy transfer from the triplet excited state, and the rate of phosphorescence is used when discussing the energy transfer from the triplet excited state. represents the coefficient constant, k n represents the rate constant of the non-radiative process (thermal deactivation and intersystem crossing) of the host molecule. , τ represents the measured lifetime of the excited state of the host molecule.

[0040]

number

[0041] First, from equation (3), the energy transfer efficiency Φ ET To increase the The rate constant k h * →g , other competing rate constants k r +k n (=1 / τ) The rate constant of the energy transfer, k h * →g Large In order to achieve this, from equations (1) and (2), the Förster mechanism and the Dexter mechanism In both of these mechanisms, the emission spectrum of the host molecule (energy from the singlet excited state) When discussing energy transfer, consider the fluorescence spectrum and energy transfer from triplet excited states. In this case, it is better to have a large overlap between the absorption spectrum of the guest molecule and the phosphorescence spectrum of the guest molecule. You can see that.

[0042] Here, the present inventors have investigated the relationship between the emission spectrum of the host molecule and the absorption spectrum of the guest molecule. When considering the overlap, the longest wavelength (lowest energy) in the absorption spectrum of the guest molecule The absorption bands on the side were considered to be important.

[0043] In this embodiment, a phosphorescent compound is used as the guest material. In the ion-excited atmosphere, the absorption band that is thought to contribute most strongly to the emission is the singlet ground state The absorption wavelength corresponding to the direct transition to the triplet excited state and its vicinity are the longest wavelengths. This is the absorption band that appears in the emission spectrum (fluorescence spectrum and The absorption band of the phosphorescent compound overlaps with the absorption band at the longest wavelength. It is considered preferable.

[0044] For example, in organometallic complexes, especially luminescent iridium complexes, the longest wavelength absorption band is , often appearing as a broad absorption band around 500-600 nm (of course, the emission wavelength (Depending on the wavelength, it may appear on the shorter or longer wavelength side.) This absorption band is mainly Triplet MLCT (Metal to Ligand Charge Transfer) r) transition. However, this absorption band contains triplet π-π * transition or singlet MLCT transition These overlap and are blown to the longest wavelength side of the absorption spectrum. In other words, it is thought that the lowest singlet excited state and the lowest triplet excited state form a broad absorption band. The difference between the excited states is small, and the absorption due to these states overlaps, resulting in the longest wavelength of the absorption spectrum. Therefore, it is considered that a broad absorption band is formed on the side of the organic gold as the guest material. When using metal complexes (especially iridium complexes), the longest wavelength band is It is preferable that the absorption band of the light-emitting element largely overlaps with the emission spectrum of the host material.

[0045] First, let us consider the energy transfer from the triplet excited state of the host material. From the theory, in the energy transfer from the triplet excited state, the phosphorescence spectrum of the host material It is sufficient that the overlap between the absorption band of the guest material on the longest wavelength side and the absorption band of the guest material is large.

[0046] Generally, fluorescent compounds are used as host materials, so the phosphorescence lifetime (τ) is expected to be more than a millisecond. Very long (k r +k n This is because the triplet excited state is converted to the ground state (singlet). This is because the transition of is a forbidden transition. From equation (3), this means that the energy transfer efficiency Φ ET Taking this into consideration, the triplet excited state of the host material is converted to the guest material. Energy transfer to the triplet excited state of a material generally tends to occur easily.

[0047] However, the problem here is the energy from the singlet excited state of the host material. In addition to the energy transfer from the triplet excited state, the energy transfer from the singlet excited state From the above discussion, if we want to efficiently transfer electrons, we must consider not only the phosphorescence spectrum of the host material but also the Furthermore, the fluorescence spectrum must be designed to overlap with the longest wavelength absorption band of the guest material. In other words, the fluorescent spectrum of the host material must be similar to the phosphorescent spectrum. Unless the host material is designed to be at such a position, the singlet excited state and triplet excited state of the host material will not be This means that energy transfer from both the excited doublet states cannot be performed efficiently. do.

[0048] However, in general, the S1 level and the T1 level are significantly different (S1 level > T1 level). The emission wavelength of light and the emission wavelength of phosphorescence are also significantly different (emission wavelength of fluorescence < emission wavelength of phosphorescence). For example, in light-emitting devices using phosphorescent compounds, 4,4 '-Di(N-carbazolyl)biphenyl (abbreviation: CBP) has a phosphorescent spectrum around 500 nm. On the other hand, the fluorescence spectrum is around 400 nm, with a gap of 100 nm. Considering this example, it is possible to determine whether the fluorescent spectrum of the host material is the same as the phosphorescent spectrum. It is extremely difficult to design a host material to be in such a position. The efficiency of energy transfer from the singlet excited state of the host material to the guest material is significantly improved. The present inventors have considered this to be a major problem.

[0049] The fluorescent compound used as the host material has a fluorescence lifetime (τ) of approximately nanoseconds. Short (k r +k n This is because the transition from the singlet excited state to the ground state (singlet) This is because the transition is an allowed transition. From equation (3), this means that the energy transfer efficiency Φ ET Against Taking this into consideration, the singlet excited state of the host material is transferred to the guest material. Generally, energy transfer is unlikely to occur.

[0050] One aspect of the present invention is to transfer energy from the singlet excited state of such a host material to a guest material. This is a useful technique that can overcome problems related to energy transfer efficiency.

[0051] Until now, phosphorescent compounds have been able to emit light in singlet and triplet excited states by utilizing intersystem crossing. Since both states can be converted into light (see "(1) Direct recombination process" above), phosphorescence It has been said that the internal quantum efficiency of a light-emitting device using such a compound can theoretically be 100%. Then, assuming that the light extraction efficiency is 20%, the light emission that reaches an external quantum efficiency of 20% There has been discussion that the internal quantum efficiency of the device is nearly 100%. However, in these conventional light-emitting devices, the singlet excited state of the host material is In fact, the internal quantum efficiency has not reached 100% because the energy transfer from This is because, by carrying out one embodiment of the present invention described below, This is because researchers have achieved an external quantum efficiency of 30%. An efficiency of 30% or more corresponds to an internal quantum efficiency of 100%, and one embodiment of the present invention achieves this. This is a useful technique for creating a photovoltaic cell. is estimated to correspond to an internal quantum efficiency of 70% or less.

[0052] <One aspect of the present invention> One aspect of the present invention is a light-emitting device comprising a phosphorescent compound, a first organic compound, and a second organic compound. The layer is disposed between a pair of electrodes, and a first organic compound and a second organic compound form an exciplex. The light-emitting element is a combination of these elements.

[0053] The first organic compound and the second organic compound are reacted with each other by recombination of carriers (or singlet excitons). The exciplex formed emits light. In this case, the emission wavelength is the emission wavelength of each of the first organic compound and the second organic compound. The wavelength of the exciplex is longer than the wavelength of the fluorescent compound. The fluorescence spectrum of the first organic compound and the fluorescence spectrum of the second organic compound are The emission spectrum can be converted to a spectrum located on the side of the

[0054] Therefore, as shown in FIG. 25, the fluorescence spectrum of the first organic compound (or the second organic compound) Even if the spectrum is located on the shorter wavelength side compared to the absorption band located on the longest wavelength side of the phosphorescent compound, Even if there is no overlap with the absorption band, the formation of an exciplex will result in emission of long wavelengths. The optical spectrum can be obtained, and the overlap with the absorption band can be increased. The light-emitting device of this invention is a device in which the emission spectrum of the exciplex overlaps with the absorption spectrum of the phosphorescent compound. This allows for high energy transfer efficiency. According to one embodiment of the present invention, a light-emitting element with high external quantum efficiency can be achieved.

[0055] In addition, since exciplexes exist only in excited states, there is no ground state that can absorb energy. Therefore, the singlet and triplet excited states of the phosphorescent compound are not converted into the exciplex. This results in a reverse energy transfer, and the phosphorescent compound is deactivated before it can emit light (i.e., the luminous efficiency This phenomenon, which impairs the external quantum efficiency, is not thought to occur in principle. This is one of the reasons why it can be so expensive.

[0056] In addition, it is considered that the difference between the singlet excitation energy and the triplet excitation energy of an exciplex is extremely small. In other words, the emission spectrum from the singlet state of the exciplex and the emission spectrum from the triplet state are The emission spectra are very close to each other. The emission spectrum (generally from the singlet state of an exciplex) of a phosphorescent compound When the design is such that the absorption band is overlapped with the longest wavelength of the compound, the triplet state of the exciplex is The emission spectra of these compounds (which are not observed at room temperature and are often not observed at low temperatures) are also This overlaps with the absorption band located at the longest wavelength side of the compound. The singlet and triplet states of the complex can be efficiently converted into phosphorescent compounds. This means that you can move the ghee.

[0057] Regarding whether exciplexes actually have such properties, we will use molecular orbital calculations to Generally, the combination of a heteroaromatic compound and an aromatic amine is The lowest unoccupied molecular orbital (LUMO) of amines The LUMO level (electrons are orbital) of heteroaromatic compounds is deeper than the LUMO level (electrons are orbital) of heteroaromatic compounds. The HOMO (Highest Occupied Molecular Orbital) of heteroaromatic compounds Aromatic amines that are shallower than the Occupied Molecular Orbital levels Due to the influence of the HOMO level of the cation (the property that holes can easily enter), exciplexes are often formed. Therefore, we investigated the dibenzo[f,h]ky, a typical skeleton that constitutes the LUMO of heteroaromatic compounds. The triamines of the representative skeletons that constitute the HOMO of aromatic amines are Calculations were performed using a combination with phenylamine (abbreviation: TPA).

[0058] First, the lowest excited singlet state (S1) and the lowest excited triplet state (T The optimal molecular structure and excitation energy in 1) were calculated using the time-dependent density functional theory (TD-DFT) ) was used for the calculation. Furthermore, the excitation energy was calculated for the dimer of DBq and TPA. The total energy of DFT is the potential energy, the electrostatic energy between electrons, and the It is expressed as the sum of the kinetic energy and the exchange-correlation energy, which includes all the complex interactions between electrons. In DFT, the exchange-correlation interaction is expressed as a generalized one-electron potential in terms of electron density. Since it is approximated by a function (meaning a function of a function), the calculation is fast and highly accurate. Using the mixed functional B3LYP, we calculated the weights of each parameter related to the exchange and correlation energy. In addition, the basis functions are 6-311 (three contraction functions for each valence orbital). The triple split valence basis set (based on the number of basis functions) is used to calculate all atoms. For example, in the case of a hydrogen atom, the 1s to 3s orbitals are considered. In the case of carbon atoms, the orbitals 1s to 4s and 2p to 4p are taken into consideration. Furthermore, to improve the accuracy of the calculation, the p function is used for the hydrogen atom as a polarization basis set, and In addition, the d function was added.

[0059] The quantum chemistry calculation program used was Gaussian 09. The analysis was carried out using a high-performance computer (SGI, Altix4700).

[0060] First, the HOMO levels and The HOMO and LUMO levels were calculated. The distribution of MO is shown in Figure 65.

[0061] Figure 65(A1) shows the LUMO distribution of DBq alone, and Figure 65(A2) shows the LUMO distribution of DBq alone. 65(B1) shows the HOMO distribution of TPA alone, and Fig. 6 5(B2) shows the distribution of the HOMO of TPA alone, and Fig. 65(C1) shows the distribution of the HOMO of DBq and TPA The LUMO distribution of the dimer of DBq and TPA is shown in Figure 65(C2). The distribution of O is shown.

[0062] As shown in Figure 64, the dimer of DBq and TPA has a LUMO level that is deeper than that of TPA ( The LUMO level of DBq (-1.99 eV) is shallower than the HOMO level of DBq ( The HOMO level of TPA (-5.21 eV) is the highest, and the exciplex of DBq and TPA is formed. In fact, as can be seen from Figure 65, the dimer of DBq and TPA The LUMO is located on the DBq side, and the HOMO is located on the TPA side.

[0063] Next, we show the excitation energies obtained from the optimal molecular structures of DBq alone at S1 and T1. Here, the excitation energies of S1 and T1 correspond to the fluorescence and phosphorescence wavelengths emitted by DBq alone, respectively. The excitation energy of S1 of DBq alone is 3.294 eV, and the fluorescence wavelength is The excitation energy of T1 of DBq alone was 2.460 eV, and the phosphorescence wavelength was 504.1 nm.

[0064] The excitation energies obtained from the optimal molecular structures of TPA alone at S1 and T1 are also shown. Here, the excitation energies of S1 and T1 correspond to the fluorescence and phosphorescence wavelengths emitted by TPA alone, respectively. The excitation energy of S1 of TPA alone is 3.508 eV, and the fluorescence wavelength is The excitation energy of T1 of TPA alone was 2.610 eV, and the phosphorescence wavelength was 474.7 nm.

[0065] Furthermore, the excitation energies obtained from the optimized molecular structures of the DBq and TPA dimers at S1 and T1 were The excitation energies of S1 and T1 are the fluorescence energies emitted by the dimer of DBq and TPA. and phosphorescence wavelengths, respectively. The excitation energy of S1 of DBq and TPA dimer is The energy of DBq and TPA was 2.036 eV and the fluorescence wavelength was 609.1 nm. The excitation energy of the dimer T1 is 2.030 eV, and the phosphorescence wavelength is 610.0 nm. It was.

[0066] From the above, for both DBq and TPA alone, the phosphorescence wavelength is shorter than the fluorescence wavelength. This is because the wavelength of the CBP (measured This shows a similar trend to that of the previous results (values), which supports the validity of the calculations.

[0067] On the other hand, the fluorescence wavelength of the dimer of DBq and TPA is higher than that of DBq alone or TPA alone. This is similar to the example (measured values) described later. This is a trend that supports the validity of the calculation. The difference between the optical wavelength and the phosphorescent wavelength is only 0.9 nm, which means that they are almost the same wavelength.

[0068] From this result, it can be seen that the exciplex has almost the same energy for the singlet excitation energy and the triplet excitation energy. Therefore, as mentioned above, the exciplex can be summarized as Efficient energy transfer from both singlet and triplet states to phosphorescent compounds It was suggested that it could be done.

[0069] This effect is unique to the use of exciplexes as a medium for energy transfer. Generally, phosphorescent compounds are excited from the singlet or triplet excited state of the host material. On the other hand, in one aspect of the present invention, the energy transfer between the host material and other First, an exciplex (an exciplex between a first organic compound and a second organic compound) is formed with the material. This method is significantly different from conventional methods in that it uses energy transfer from the exciplex. These differences have resulted in an unprecedentedly high luminous efficiency.

[0070] Generally, when an exciplex is used in the light-emitting layer of a light-emitting element, it is possible to control the color of emitted light. Although they are valuable, the luminescence efficiency is usually significantly reduced. It has been thought that such a light-emitting device is not suitable for obtaining a highly efficient light-emitting device. However, as shown in one embodiment of the present invention, the exciplex is used as a catalyst for energy transfer to a phosphorescent compound. The inventors have found that by using the material in the body, the luminous efficiency can be increased to the maximum. This is a technological concept that contradicts conventional stereotypes.

[0071] In order to ensure sufficient overlap between the emission spectrum of the exciplex and the absorption spectrum of the guest material, The peak energy of the emission spectrum and the lowest energy absorption of the absorption spectrum are It is preferable that the difference between the energy value of the absorption peak and the energy value of the absorption peak is within 0.3 eV. It is preferably within 0.2 eV, and most preferably within 0.1 eV.

[0072] In one embodiment of the present invention, a singlet exciton of the first organic compound or the second organic compound is From this, an exciplex is formed.

[0073] In a light-emitting element of one embodiment of the present invention, one of the first organic compound and the second organic compound is a singlet After forming an exciton, the elementary process of forming an exciplex by interacting with another one in the ground state is As mentioned above, the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound Since the electrons can be overlapped to a large extent, the energy transfer efficiency can be increased. As a result, a light emitting device with high external quantum efficiency can be realized.

[0074] In addition, as mentioned above, singlet excitons have a short excitation lifetime (small τ). Before the excitation energy is transferred from the molecule to the guest material, a part of the excitation energy is deactivated (emission or thermal deactivation) (Φ in Equation (3) ET The tendency is for However, in one aspect of the present invention, singlet excitons rapidly form exciplexes. This prevents the deactivation of the excitation energy. The excitation lifetime of the nucleus is relatively long, so the energy transfer efficiency Φ ET It is considered to be advantageous for Therefore, the singlet excitation of the host material is thought to affect not only the efficiency but also the lifetime of the device. By applying one embodiment of the present invention, deactivation of electromotive energy can be suppressed, and the lifetime can be extended. Therefore, a light emitting device with a long lifetime can be realized.

[0075] In the light-emitting element of one embodiment of the present invention, the excitation energy of the exciplex is transferred to a phosphorescent compound. It is preferred that the energy transfer is sufficient so that substantially no emission from the exciplex is observed. Therefore, energy is transferred to the phosphorescent compound via the exciplex, and the phosphorescent compound Preferably, the material emits phosphorescence.

[0076] Furthermore, based on the concept of energy transfer described above, the first organic compound and the second organic compound At least one of the compounds is a fluorescent compound (i.e., the compound is easily luminescent or thermally deactivated from the singlet excited state). Therefore, when the first organic compound is a compound having a structure similar to that of the first organic compound, an embodiment of the present invention is effective. At least one of the first organic compound and the second organic compound is preferably a fluorescent compound.

[0077] When a phosphorescent compound is used as the organic compound used as the host material, the organic compound itself emits light. In this case, the organic compound However, the organic compound serving as the host material has the problem of concentration quenching. Therefore, it is difficult to achieve high luminous efficiency. It is preferable that the compound has the above-mentioned structure and transfers energy.

[0078] In one embodiment of the present invention, the phosphorescent compound is preferably an organometallic complex.

[0079] The exciplex used in one embodiment of the present invention will be described in detail below.

[0080] <Exciplex> An exciplex is an excited state complex between different molecules. The exciplex is formed by the interaction of a material with a relatively deep LUMO level and a material with a shallow LUMO level. It is generally known that they are easily formed between materials that have the same HOMO level.

[0081] The emission wavelength depends on the energy difference between the HOMO and LUMO levels. If the energy difference is large, the emission wavelength will be short, and if the energy difference is small, the emission wavelength will be long.

[0082] Here, the HOMO levels of the first organic compound and the second organic compound used in one embodiment of the present invention are The HOM and LUMO levels of the first organic compound are different. O level < HOMO level of the second organic compound < LUMO level of the first organic compound < LUMO level of the second organic compound The LUMO levels of organic compounds are higher (see Figure 17).

[0083] When these two organic compounds form an exciplex, the LUMO level of the exciplex The HOMO level comes from the first organic compound, and the HOMO level comes from the second organic compound (Figure 1 7). Therefore, the energy difference of the exciplex is the energy difference of the first organic compound, The energy difference between the first organic compound and the second organic compound is smaller than that between the first organic compound and the second organic compound. The emission wavelength of the exciplex is longer than that of each of the organic compounds.

[0084] The process of forming the exciplex used in one embodiment of the present invention can be roughly divided into two processes.

[0085] ≪Electroplex≫ As used herein, an electroplex refers to a compound consisting of a first organic compound in the ground state and a second organic compound in the ground state. This refers to the direct formation of an exciplex from a second organic compound in the fluorine-containing state.

[0086] As mentioned above, in general, when electrons and holes recombine in a host material, they form an excited state. Excitation energy is transferred from the host material to the guest material, and the guest material reaches an excited state, emitting light. do.

[0087] Here, before the excitation energy is transferred from the host material to the guest material, the host material itself They lose some of their excitation energy by emitting light or by converting the excitation energy into heat energy. In particular, when the host material is in a singlet excited state, it is active when it is in a triplet excited state. Because the excitation lifetime is shorter than that of the singlet excited state, the singlet excited state energy is easily deactivated. The deactivation of the electrons is one of the factors that leads to a shortened life of the light-emitting element.

[0088] However, in one embodiment of the present invention, the first organic compound and the second organic compound have a carrier. To form an electroplex from the excited state (cation or anion), In other words, the formation of singlet excitons can be suppressed. There is a process of directly forming an exciplex without the need for a singlet excitation. Therefore, it is possible to realize a light-emitting element with a long life. can.

[0089] For example, the first organic compound is an electron-trapping compound, and the second organic compound is a hole-trapping compound. In the case of a compound with trapping properties, the anion of the first organic compound and the cationic In this way, electroplexes are formed directly from the host material. The generation of singlet excited states of the material is suppressed, and energy is transferred from the electroplex to the guest material. The concept of obtaining a light-emitting element with high luminous efficiency by migration has not been known before. The generation of the excited doublet state is also suppressed, and direct electroplex formation is achieved. It is believed that energy is transferred from the electroplex to the guest material. Not before.

[0090] The emission spectrum of the formed electroplex was also The wavelengths are longer than those of the organic compounds.

[0091] The emission spectrum of the first organic compound (or the second organic compound) and the absorption spectrum of the phosphorescent compound The emission spectrum of the electroplex and the absorption spectrum of the phosphorescent compound overlap rather than overlapping with the spectrum. The light-emitting element of one embodiment of the present invention is an electroplex The overlap between the emission spectrum of the phosphorescent compound and the absorption spectrum of the phosphorescent compound is used to Therefore, in one aspect of the present invention, the energy transfer efficiency is high. A light emitting device with high photoluminescence efficiency can be realized.

[0092] <Exciplex formation by excitons> Another process is when one of the first organic compound and the second organic compound generates a singlet exciton. After forming the exciplex, it interacts with the other one in the ground state to form an exciplex. Unlike electroplexing, in this case, once the first organic compound or the second organic compound is However, this is quickly converted to an exciplex, This also suppresses the deactivation of singlet excitation energy. This can prevent the first organic compound or the second organic compound from quenching the excitation energy. Therefore, in one embodiment of the present invention, a light-emitting element with a long lifetime can be realized. The triplet excited state of the ion-doped material is also rapidly converted into an exciplex, and the exciplex is converted into a guest molecule. It is thought that energy is transferred to the support material.

[0093] The emission spectrum of the formed exciplex is the same as that of the first organic compound and the second organic compound. It exists on the longer wavelength side compared to the respective emission wavelengths.

[0094] The emission spectrum of the first organic compound (or the second organic compound) and the absorption spectrum of the phosphorescent compound The emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound overlap rather than overlapping with the spectrum of the The light-emitting element of one embodiment of the present invention has an emission spectrum of an exciplex and an emission spectrum of a phosphorescent Energy transfer is achieved by utilizing the overlap of the absorption spectrum with that of the ionic compound. Therefore, in one embodiment of the present invention, a light-emitting element with high external quantum efficiency is realized. It can be realized.

[0095] For example, the first organic compound is an electron trapping compound, while the second organic compound is These compounds have hole-trapping properties. The difference between the HOMO levels and the LUMO levels of these compounds is When the difference is large (specifically, the difference is 0.3 eV or more), the electrons are selectively transferred to the first organic compound. The hole selectively enters the second organic compound. In this case, the excited state is The process of electroplex formation takes precedence over the process of complex formation. It is thought that...

[0096] This embodiment mode can be combined with other embodiment modes as appropriate.

[0097] (Embodiment 2) In this embodiment, a light-emitting element of one embodiment of the present invention will be described with reference to FIGS.

[0098] FIG. 16(A) shows a light-emitting device having an EL layer 102 between a first electrode 103 and a second electrode 108. 16(A) is a diagram showing an optical element. The light emitting element in FIG. 16(A) has a first electrode 103 and a second electrode 104. A hole injection layer 701, a hole transport layer 702, a light emitting layer 703, an electron transport layer 704, and an electron It is composed of a dopant injection layer 705 and a second electrode 108 provided thereon.

[0099] The first electrode 103 is made of a metal or alloy having a large work function (specifically, 4.0 eV or more). , conductive compounds, and mixtures thereof are preferably used. , indium tin oxide (ITO), silicon or Indium oxide-tin oxide and indium oxide-zinc oxide (Indium oxide) containing silicon oxide Indium oxide containing tungsten oxide and zinc oxide These conductive metal oxide films are usually formed by sputtering. However, it can also be produced by applying the sol-gel method. The indium-zinc oxide film is a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. The IWZO film can be formed by sputtering using a SiO2 nozzle. Contains 0.5 to 5 wt% tungsten oxide and 0.1 to 1 wt% zinc oxide relative to indium It can be formed by sputtering using a target having a graphite layer. Phen, gold, platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, Examples include palladium, nitrides of metal materials (for example, titanium nitride), and the like.

[0100] However, the layer of the EL layer 102 formed in contact with the first electrode 103 is an organic compound, which will be described later. When the electrode is formed using a composite material made by mixing a compound and an electron acceptor, The material used for the first electrode 103 may be any of various metals, alloys, and Electrically conductive compounds and mixtures thereof can be used. For example, aluminum It is also possible to use alloys containing aluminum, silver, and aluminum (for example, Al-Si).

[0101] The first electrode 103 is formed by, for example, sputtering or vapor deposition (including vacuum deposition). It can be achieved.

[0102] The second electrode 108 is made of a metal, alloy, or electrode having a small work function (preferably 3.8 eV or less). It is preferable to form the conductive layer using a conductive compound or a mixture thereof. Elements in Groups 1 and 2 of the periodic table, i.e., alkalis such as lithium and cesium Alkaline earth metals such as lithium metals, calcium, strontium, magnesium, and the like Alloys containing these elements (e.g., Mg-Ag, Al-Li), europium, ytterbium, etc. In addition to rare earth metals and alloys containing these, aluminum, silver, etc. can also be used.

[0103] However, the layer of the EL layer 102 formed in contact with the second electrode 108 is an organic compound, which will be described later. When a composite material is used in which a compound and an electron donor (donor) are mixed, the work function is large. Regardless of size, indium oxide containing Al, Ag, ITO, silicon or silicon oxide A variety of conductive materials can be used, such as tin oxide.

[0104] When forming the second electrode 108, a vacuum deposition method or a sputtering method may be used. In addition, when using silver paste, the coating method or inkjet method can be used. It can be used.

[0105] The EL layer 102 has at least a light-emitting layer 703. A known material is used in a part of the EL layer 102. It is also possible to use either a low molecular weight compound or a high molecular weight compound. The material forming the EL layer 102 is not limited to materials consisting of only organic compounds. This also includes a configuration that partially contains an inorganic compound.

[0106] The EL layer 102 includes a light-emitting layer 703 and a material having a high hole injection property as shown in FIG. a hole injection layer 701 containing a material with high hole transport properties; a hole transport layer 702 containing a material with high hole transport properties; an electron transport layer 704 containing a substance with high electron transport properties; It is formed by appropriately combining and laminating the electron injection layer 705 and the like.

[0107] The hole-injection layer 701 is a layer containing a substance with a high hole-injection property. The oxides are molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, Aluminum oxide, Chromium oxide, Zirconium oxide, Hafnium oxide, Tantalum oxide, Silver Metal oxides such as oxides of tungsten, manganese, etc. can be used. Phthalocyanine (abbreviation: HPc), copper(II) phthalocyanine (abbreviation: CuPc) Phthalocyanine compounds such as the above can be used.

[0108] In addition, the low molecular weight organic compound 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 DPAB, 4,4'-bis(N-{4-[N'-(3-methylphenyl)- N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated as DNTP D), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino] 3-[N-(9-phenylcarbazol-3-yl)benzene (abbreviation: DPA3B) )-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3, 6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9- Phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-( 9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: P Aromatic amine compounds such as CzPCN1) can be used.

[0109] Furthermore, polymeric compounds (oligomers, dendrimers, polymers, etc.) can also be used. For example, poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriflate) Phenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenyl (N'-phenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide (abbreviation: PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bi Examples include polymer compounds such as [poly(phenyl)benzidine] (abbreviation: Poly-TPD). In addition, poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS), polyaniline / poly(styrene sulfonate) (PAni / PS A polymer compound to which an acid such as methyl methyl stearate (S) is added can be used.

[0110] The hole injection layer 701 is formed by mixing an organic compound and an electron acceptor. Such composite materials may be used in which the electron acceptor is attached to the organic compound. Since holes are generated, the organic compound has excellent hole injection and hole transport properties. The material is preferably a material that is excellent in transporting generated holes (a material with high hole transport properties). It's nice.

[0111] The organic compounds used in the composite materials include aromatic amine compounds, carbazole derivatives, aromatic Various compounds such as aromatic hydrocarbons and polymer compounds (oligomers, dendrimers, polymers, etc.) As the organic compound used for the composite material, a compound having a high hole transporting property can be used. It is preferable that the organic compound is a low-molecular-weight organic compound. -6 cm 2 Hole transfer above / Vs However, it is preferable that the material has a higher hole transporting property than the electron transporting property. In the following, organic compounds that can be used in composite materials will be described. The compounds are specifically listed below.

[0112] Examples of organic compounds that can be used in composite materials include TDATA and MTDATA. , DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN 1,4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl Nyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4-phenyl -4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFL Aromatic amine compounds 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] phenyl]-9H-carbazole (abbreviation: PCzPA), 1,4-bis[4-(N-carbazole) Carbazole derivatives such as [2,3,5,6-tetraphenyl]-2,3,5,6-zolylphenyl can be used.

[0113] In addition, 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-t ert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: tB uDBA), 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 , 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, and other aromatic compounds Aromatic hydrocarbon compounds can be used.

[0114] Furthermore, 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, Thracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-buthylene) (ethyl)perylene, pentacene, coronene, 4,4'-bis(2,2-diphenylvinyl) Biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl) Aromatic hydrocarbon compounds such as diphenylanthracene (abbreviation: DPVPA) can be used. can.

[0115] The electron acceptor is 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroethylene. Organic compounds such as fluoroquinodimethane (abbreviated as F4-TCNQ) and chloranil, and transition metals In addition, metal oxides belonging to groups 4 to 8 of the periodic table can be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, Chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are electrically Among them, molybdenum oxide is particularly stable in the atmosphere and has a high molecular acceptability. It is preferred because it has low moisture content and is easy to handle.

[0116] In addition, the above-mentioned polymer compounds such as PVK, PVTPA, PTPDMA, and Poly-TPD A composite material may be formed using the above-described electron acceptor and used for the hole-injection layer 701.

[0117] The hole transport layer 702 is a layer containing a substance with a high hole transport property. NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluoromethyl] 4,4-Diphenyl-2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), '-Bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino] Aromatic amine compounds such as biphenyl (abbreviation: BSPB) can be used. The substances mentioned are mainly 10 -6 cm 2 / Vs or more. Any substance other than these may be used as long as it has a higher hole transporting property than an electron transporting property. The layer containing a substance with a high hole transporting property may be a single layer or may be two or more layers containing the above substance. It may also be laminated on top.

[0118] The hole transport layer 702 may also contain carbazole derivatives such as CBP, CzPA, and PCzPA. Anthracene derivatives such as t-BuDNA, DNA, and DPAnth may also be used. stomach.

[0119] The hole transport layer 702 may be made of a material such as PVK, PVTPA, PTPDMA, or Poly-TPD. Any polymeric compound can be used.

[0120] The light-emitting layer 703 is a layer containing a light-emitting substance. The phosphorescent compound includes a light-emitting material, a first organic compound, and a second organic compound. The first organic compound and the second organic compound are the guest material. The material that is contained in a larger amount is the host material. do.

[0121] As the phosphorescent compound, an organometallic complex is preferred, and an iridium complex is particularly preferred. Considering the energy transfer by the Förster mechanism described above, the longest wavelength of the phosphorescent compound The molar absorption coefficient of the absorption band located on the long side is 2000M -1 ·cm -1 More than 5 is preferable. 000M -1 ·cm-1 The above is particularly preferred. Examples of compounds include bis(3,5-dimethyl-2-phenylpyrazinato)(dipivalo) Ir(mppr-Me)2(dpm) ) and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(I II) (abbreviation: [Ir(dppm)2(acac)]), bis(2,3,5-triphenyl Iridium(III) (Ir(tpp) r)2(dpm)]), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinium dinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), (acetonitrile (6-tert-butyl-4-phenylpyrimidinato)iridium (III) (abbreviation: [Ir(tBuppm)2(acac)]) and the like. , such as [Ir(dppm)2(acac)], with a molar extinction coefficient of 5000M -1 ·cm -1 By using materials that achieve this or higher, a light-emitting device with an external quantum efficiency of approximately 30% can be obtained. do.

[0122] Examples of the first organic compound and the second organic compound include 2-[3-(dibenzothiophene)-2-(2-methyl-2-propanol]-1, 2-[3-(dibenzothiophene) ... (4-phenyl)dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDB q-II), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl] 1,2-Dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-( Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7 mDBTPDBq-II) and 6-[3-(dibenzothiophen-4-yl)phenyl 1]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II), 2-[4- (Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazo Compounds that readily accept electrons, such as DBTBIm-II (representatively, heteroaromatic compounds) and 4,4'-bis[N-(1-naphthyl)-N- phenylamino]biphenyl (abbreviation: NPB or α-NPD), 4-phenyl-4'- (9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA 1BP), and 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbamoyl) PCBNBB, 4-(1-naphthyl)-3-benzoltriphenylamine )-4'-phenyltriphenylamine (abbreviation: αNBA1BP), 2,7-bis[N- (4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9'-bifulv Diphenylmethane (abbreviation: DPA2SF), 4,4',4''-tris[N-(1-naphthyl)-N -phenylamino]triphenylamine (abbreviation: 1'-TNATA), 9-phenyl-9 H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCC Compounds that readily accept holes (typically aromatic amine compounds and carboxylic acid compounds) such as It is preferable to combine it with any one of the above compounds (e.g., benzol compounds). By doing so, the effect of improving the luminescence efficiency and lifetime due to the energy transfer from the exciplex can be achieved. Light emission is achieved by balancing the carriers between hole transport and electron transport in the light-emitting layer. The effects of improving efficiency and lifetime can also be obtained. However, the present invention is not limited to these. Any combination that can form the above is acceptable.

[0123] The exciplex may be formed at the interface between the two layers. When a layer containing a first organic compound and a layer containing a second organic compound are stacked, an exciplex is formed near the interface. However, these two layers may be used as the light-emitting layer in one embodiment of the present invention. The photosensitive compound may be added in the vicinity of the interface. It is sufficient if it is added to one or both of them.

[0124] The electron-transporting layer 704 is a layer containing a substance with a high electron-transporting property. The following is a list of aluminum compounds: Alq3, tris(4-methyl-8-quinolinolato)aluminum (abbreviated as Alm q3), bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq 2), BAlq, Zn(BOX)2, bis[2-(2-hydroxyphenyl)benzothiazolinone] Zn(BTZ)2 and other metal complexes. -biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazo PBD, 1,3-bis[5-(p-tert-butylphenyl)-1,3 ,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-ter t-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triacontria TAZ (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)- p-EtTA Z), bathophenanthroline (abbreviated as BPhen), bathocuproine (abbreviated as BCP) , 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: Bz Heteroaromatic compounds such as poly(2,5-pyridine-Os) can also be used. diyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl) -co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), poly[(9,9-di octylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl) Polymer compounds such as PF-BPy can also be used. The substances that were found were mainly 10 -6 cm 2 It is a substance with an electron mobility of 1 / Vs or more. Any substance other than those mentioned above may be used for the electron transport layer as long as it has a higher electron transporting property than the above-mentioned substances. stomach.

[0125] The electron transport layer may be a single layer or a laminate of two or more layers made of the above-mentioned materials. It may also be possible to

[0126] The electron injection layer 705 is a layer containing a substance with a high electron injection property. lithium, cesium, calcium, lithium fluoride, cesium fluoride, calcium fluoride, Alkali metals, alkaline earth metals, or compounds thereof, such as lithium oxide, are used. Also, rare earth metal compounds such as erbium fluoride can be used. In addition, the above-described materials for forming the electron transporting layer 704 can also be used.

[0127] Alternatively, the electron injection layer 705 may be formed of a compound material obtained by mixing an organic compound and an electron donor (donor). Such composite materials are formed by adding electrons to an organic compound via an electron donor. In this case, the organic compound It is preferable that the material is excellent in transporting the generated electrons. Specifically, for example, The material (metal complex, heteroaromatic compound, etc.) constituting the electron transport layer 704 can be used. The electron donor may be any substance that exhibits electron donating properties to organic compounds. In particular, alkali metals, alkaline earth metals and rare earth metals are preferred, and lithium, cesium , magnesium, calcium, erbium, ytterbium, etc. Potassium metal oxides and alkaline earth metal oxides are preferred, and lithium oxide and calcium oxide are also preferred. Examples include barium oxide and the like. Lewis bases such as magnesium oxide are also used. It is also possible to use organic compounds such as tetrathiafulvalene (TTF). It is also possible.

[0128] The hole injection layer 701, the hole transport layer 702, the light emitting layer 703, and the electron transport layer 704 The electron injection layer 705 is formed by a deposition method (including a vacuum deposition method), an ink jet method, a coating method, respectively. It can be formed by a method such as a fabric method.

[0129] As shown in FIG. 16(B), the EL layer is formed by multiple layers between the first electrode 103 and the second electrode 108. In this case, the first EL layer 800 and the second EL layer 80 It is preferable to provide a charge generating layer 803 between the above-mentioned layers. The charge generating layer 803 can be formed of a layer made of a composite material and another material. In this case, the layer made of the other material may be a layer made of an electron donor. A layer containing a conductive material and a material with high electron transport properties, a layer made of a transparent conductive film, or the like can be used. A light-emitting element having such a structure can cause problems such as energy transfer and quenching. This will allow for a wider range of material choices, resulting in light-emitting devices with both high luminous efficiency and long life. It is also easy to obtain phosphorescence in one EL layer and fluorescence in the other. This structure can be used in combination with the above-mentioned EL layer structure.

[0130] In addition, by making the luminescent color of each EL layer different, the desired luminescent color can be obtained as a whole. For example, in a light-emitting element having two EL layers, the first By making the luminescent color of the first EL layer and the luminescent color of the second EL layer complementary to each other, It is also possible to obtain a light-emitting device that emits white light as a whole. The same applies to the case of a light emitting element having a

[0131] As shown in FIG. 16(C), the EL layer 102 is formed by connecting the first electrode 103 and the second electrode 108. Between them, there are 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. the input buffer layer 706, the electronic relay layer 707, and the composite layer in contact with the second electrode 108. 708.

[0132] By providing the composite material layer 708 in contact with the second electrode 108, it is possible to form a thin film by using a sputtering method in particular. Therefore, when the second electrode 108 is formed, damage to the EL layer 102 can be reduced. The composite material layer 708 is preferably formed using the above-described organic compound having a high hole transporting property. Composite materials containing acceptor substances can be used.

[0133] Furthermore, by providing an electron injection buffer layer 706, the composite material layer 708 and the electron transport layer 7 Since the injection barrier between the composite material layer 708 and the electrode 704 can be reduced, the electrons generated in the composite material layer 708 can be injected into the electrode 704. The electron transport layer 704 can be easily injected.

[0134] The electron injection buffer layer 706 contains an alkali metal, an alkaline earth metal, a rare earth metal, and and their compounds (alkali metal compounds (oxides such as lithium oxide, halides, carbonates) Alkaline earth metal compounds (including carbonates such as lithium and cesium carbonate), oxides, halides compounds of rare earth metals (including oxides, halides, carbonates) or rare earth metal compounds (including oxides, halides, carbonates) It is possible to use a substance with high electron injection properties, such as tetrahydrofuran (Tetrahydrofuran) and tetrahydrofuran (Tetrahydrofuran).

[0135] The electron-injecting buffer layer 706 is formed by containing a substance with high electron transporting properties and a donor substance. When the compound is formed, the mass ratio to the substance having high electron transport properties is 0.001 or more and 0.1 or less It is preferable to add the donor substance in the ratio of Alkali metals, alkaline earth metals, rare earth metals, and their compounds (alkali metal compounds ( Contains oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate ), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth metals In addition to compounds of the group (including oxides, halides, and carbonates), tetrathianaphthacene (abbreviated Organic compounds such as TTN, nickelocene, and decamethylnickelocene can also be used. Note that the substance with a high electron transporting property can be the same as the material of the electron transporting layer 704 described above. The substrate can be formed using a variety of materials.

[0136] Furthermore, an electron relay layer 707 is formed between the electron injection buffer layer 706 and the composite material layer 708. The electron relay layer 707 is not necessarily provided, but it is preferable to form the electron relay layer 707. By providing the electron relay layer 707 with high transportability, electrons can be transferred to the electron injection buffer layer 706. It will be possible to send it quickly.

[0137] An electron relay layer 707 is sandwiched between the composite material layer 708 and the electron injection buffer layer 706. The structure is composed of an acceptor material contained in a composite material layer 708 and an electron injection buffer layer 70 The structure is such that it is less likely to interact with the donor substance contained in 6 and to inhibit each other's functions. Therefore, an increase in the driving voltage can be prevented.

[0138] The electron relay layer 707 contains a substance with high electron transport properties, and the LUM of the substance with high electron transport properties The O level is determined by the LUMO level of the acceptor material contained in the composite material layer 708 and the electron transport The layer 704 is formed so as to have a LUMO level between that of the highly electron-transporting substance contained in the layer 704 . In addition, when the electron relay layer 707 contains a donor material, the donor phase of the donor material The LUMO level of the acceptor material in the composite material layer 708 and the LUMO level of the electron transport layer 704 The LUMO level of the material with high electron transport properties is set to be between the specific energy The energy level of the material with high electron transport properties contained in the electron relay layer 707 is The MO level is set to -5.0 eV or more, preferably -5.0 eV or more and -3.0 eV or less. stomach.

[0139] The electron relay layer 707 contains a material with high electron transport properties, such as a phthalocyanine-based material. It is preferable to use a metal complex having a metal-oxygen bond and an aromatic ligand.

[0140] The phthalocyanine-based material contained in the electron relay layer 707 is specifically CuPc, S nPc (Phthalocyanine tin(II) complex), ZnPc (Phthalocyanine zinc complex), CoPc (Cobal t(II)phthalocyanine, β-form), FePc(Phthal ocyanine Iron) and PhO-VOPc(Vanadyl 2,9,16, 23-tetraphenoxy-29H,31H-phthalocyanine) It is preferable to use either one.

[0141] The metal complexes having a metal-oxygen bond and an aromatic ligand contained in the electron relay layer 707 include: It is preferable to use a metal complex having a metal-oxygen double bond. In this case, the molecule has acceptor properties (the ability to easily accept electrons), which facilitates electron transfer (donation and receipt). In addition, metal complexes with metal-oxygen double bonds are thought to be stable. Therefore, by using a metal complex having a metal-oxygen double bond, it is possible to obtain a light-emitting device with low This makes it possible to drive the device more stably with a voltage.

[0142] As a metal complex having a metal-oxygen bond and an aromatic ligand, a phthalocyanine-based material is preferred. Specifically, VOPc (vanadyl phthalocyanine), SnO Pc(Phthalocyanine tin(IV) oxide complex) and TiOPc (Phthalocyanine titanium oxide co complex) is a molecule in which the metal-oxygen double bond acts on other molecules. This is preferred because it is easy to do and has high acceptor properties.

[0143] The above-mentioned phthalocyanine-based material preferably has a phenoxy group. Specifically, a phthalocyanine derivative having a phenoxy group, such as PhO-VOPc, is preferred. The phthalocyanine derivative having a phenoxy group is soluble in a solvent. It has the advantage of being easy to handle when forming a light-emitting element. This has the advantage that maintenance of the device used for film formation becomes easier.

[0144] The electron relay layer 707 may further contain a donor material. Alkali metals, alkaline earth metals, rare earth metals and their compounds (alkali metal compounds) (Oxides such as lithium oxide, halides, carbonates such as lithium carbonate and cesium carbonate (including oxides, halides, and carbonates), or rare earth metal compounds Compounds of metals (including oxides, halides, and carbonates), as well as tetrathianaphthacene (abbreviation: TTN), nickelocene, decamethylnickelocene, and other organic compounds are used. By including these donor materials in the electron relay layer 707, This facilitates movement, and the light-emitting element can be driven at a lower voltage.

[0145] When the electron-relay layer 707 contains a donor substance, the above-mentioned In addition to the material, the acceptor level of the acceptor substance contained in the composite material layer 708 A substance with a high LUMO level can be used. Specific energy levels are: , and the LUMO level is in the range of -5.0 eV or more, preferably in the range of -5.0 eV or more and -3.0 eV or less. It is preferable to use a substance having a structure such as a perylene derivative. Nitrogen-containing condensed aromatic compounds are examples of such compounds. Therefore, it is a preferable material to be used for forming the electron relay layer 707. do.

[0146] Specific examples of perylene derivatives include 3,4,9,10-perylenetetracarboxylic dianhydride. (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxylic bisbenzyl Zoimidazole (abbreviation: PTCBI), N,N'-dioctyl-3,4,9,10-periodic Phenylenetetracarboxylic diimide (abbreviation: PTCDI-CH), N,N'-dihexyl- 3,4,9,10-perylenetetracarboxylic diimide (abbreviation: Hex PTC) It can be obtained.

[0147] Specific examples of nitrogen-containing condensed aromatic compounds include pyrazino[2,3-f][1,10] Phenanthroline-2,3-dicarbonitrile (PPDN), 2,3,6,7,1 0,11-Hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation :HAT(CN)6), 2,3-diphenylpyrido[2,3-b]pyrazine (abbreviation: 2P YPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (abbreviation :F2PYPR) etc.

[0148] Other examples include 7,7,8,8-tetracyanoquinodimethane (TCNQ), 1,4, 5,8-Naphthalenetetracarboxylic dianhydride (abbreviation: NTCDA), Perfluorinated phthalocyanine, copper hexadecafluorophthalocyanine (abbreviation: F 16 CuPc), N,N'-bi S(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoro (N-octyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (abbreviation: NTCD I-C8F), 3',4'-dibutyl-5,5''-bis(dicyanomethylene)-5,5 ''-Dihydro-2,2':5',2''-terthiophene) (abbreviation: DCMT), meta fullerenes (e.g., [6,6]-phenyl C 61 Butyric acid methyl ester) This can be done.

[0149] When the electron-relay layer 707 contains a donor substance, the electron-relay layer 707 contains a substance with high electron transporting properties and a donor substance. The electron relay layer 707 may be formed by a method such as co-evaporation with an insulating material.

[0150] The hole injection layer 701, the hole transport layer 702, the light emitting layer 703, and the electron transport layer 704 are made of the above-mentioned materials. Each can be formed using the material.

[0151] In this manner, the EL layer 102 of this embodiment can be manufactured.

[0152] The light-emitting element described above emits light due to a potential difference generated between the first electrode 103 and the second electrode 108. A current flows, and holes and electrons recombine in the EL layer 102, causing light to be emitted. This light emission is emitted by either the first electrode 103 or the second electrode 108 or both. Therefore, the current is taken out to the outside through either the first electrode 103 or the second electrode 108. One or both of the electrodes are transparent to visible light.

[0153] The structure of the layer provided between the first electrode 103 and the second electrode 108 is the same as that described above. In order to prevent quenching caused by the proximity of the light emitting region to the metal, A light-emitting region where holes and electrons recombine is formed at a location away from the first electrode 103 and the second electrode 108. Any other configuration may be used as long as it provides a region.

[0154] That is, the layer stack structure is not particularly limited, and a material having a high electron transporting property, a material having a high hole transporting property, High electron injection material, high hole injection material, bipolar material (electron and A layer made of a material with high hole transportability or a hole blocking material can be freely combined with the light-emitting layer. It can be configured by combining them.

[0155] A passive matrix light-emitting device or a transistor light-emitting device can be manufactured by using the light-emitting element described in this embodiment mode. An active matrix light-emitting device is fabricated in which the driving of the light-emitting element is controlled by a gate. The light-emitting device can be applied to electronic devices, lighting devices, and the like.

[0156] In the above manner, a light-emitting element of one embodiment of the present invention can be manufactured.

[0157] This embodiment mode can be combined with other embodiment modes as appropriate. [Example]

[0158] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of a second organic compound and a phosphorescent compound will be described with reference to FIG. 1. .

[0159] The phosphorescent compound used in this example is bis(3,5-dimethyl-2-phenylpyrazinato) (Dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2( dpm)]). The first organic compound used in this example is 2-[3-(dibenzo[3-(diphenyl ether)]]. 2m(2-methyl-4-phenyl)dibenzo[f,h]quinoxaline (abbreviation: 2mDB TPDBq-II). The second organic compound used in this example is 4,4'-dichloro-4,4'-diphenyl ether. (1-naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenyl The chemical formula of the material used in this example is shown below: .

[0160] [ka]

[0161] <Absorption spectrum> Figure 1(A)(B) shows the structure of the phosphorescent compound [Ir(mppr-Me)2(dpm)]. 1 shows the ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the dichloromethane solution. The absorption spectrum was measured using an ultraviolet-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). Then, a dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were carried out at room temperature. It was.

[0162] <Emission spectrum> In addition, Figure 1(A)(B) shows the thin film of the first organic compound, 2mDBTPDBq-II. Emission spectrum (Emission spectrum 1), the emission spectrum of a thin film of the second organic compound, PCBNBB. Optical spectrum (emission spectrum 2) and the mixture of 2mDBTPDBq-II and PCBNBB The emission spectrum of the thin film of the composite material (emission spectrum 3) is shown in Figure 1(A). indicates the wavelength (nm), and the vertical axis indicates the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity ( In FIG. 1(B), the horizontal axis represents energy (eV), and the vertical axis represents Molar extinction coefficient ε (M-1 ·cm -1 ) and luminescence intensity (arbitrary units).

[0163] From the absorption spectrum of Figure 1(A), [Ir(mppr-Me)2(dpm)] is It can be seen that the fluorine-containing compound has a broad absorption band around 100 nm. This absorption band strongly contributes to the emission of light. It is thought to be an absorption band.

[0164] Emission spectrum 3 has a peak at a longer wavelength (lower energy) than emission spectra 1 and 2. The peak of the emission spectrum 3 is larger than the peaks of the emission spectra 1 and 2. , which is located close to the absorption band. The emission spectrum that overlaps most with the contributing absorption band is emission spectrum 3. Specifically, the peak of the absorption band in the absorption spectrum (the signal around 520 nm) The difference between the peak of the upper limit and the peak of the emission spectrum 3 was 0.04 eV.

[0165] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBNBB is It was found that the spectrum has a peak on the longer wavelength (lower energy) side. Therefore, by mixing 2mDBTPDBq-II and PCBNBB, an exciplex was formed. It was suggested that this is the case.

[0166] The emission spectrum of the mixed material is similar to the absorption spectrum of [Ir(mppr-Me)2(dpm)]. It was found that there is a large overlap with the absorption band that is thought to strongly contribute to the luminescence in the SiO2 / ... Therefore, the mixed material of 2mDBTPDBq-II and PCBNBB and [Ir(mppr- The light-emitting element using the mixed material has the emission spectrum of the phosphorescent compound Energy transfer is achieved by utilizing the overlap of the absorption spectrum of Therefore, it is possible to obtain a light-emitting device with high external quantum efficiency. was suggested. [Example]

[0167] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. 2. .

[0168] The phosphorescent compound used in this example is (acetylacetonato)bis(4,6-diphenylpiperidin). (Ir(dppm)2(acac)]) The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is PCBNBB. Materials used in this example The chemical formula of the material is shown below: The chemical formula of the material used in Example 1 is omitted.

[0169] [ka]

[0170] <Absorption spectrum> Figure 2(A)(B) shows the dichloromethane of the phosphorescent compound [Ir(dppm)2(acac)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the methane solution is shown below. The spectrum was measured using an ultraviolet-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were performed at room temperature. .

[0171] <Emission spectrum> In addition, Figure 2(A)(B) shows the thin film of the first organic compound, 2mDBTPDBq-II. Emission spectrum (Emission spectrum 4), the emission spectrum of a thin film of the second organic compound, PCBNBB. Optical spectrum (emission spectrum 5) and the mixture of 2mDBTPDBq-II and PCBNBB The emission spectrum of the thin film of the composite material (emission spectrum 6) is shown in FIG. indicates the wavelength (nm), and the vertical axis indicates the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity ( In FIG. 2(B), the horizontal axis represents energy (eV), and the vertical axis represents Molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary units).

[0172] From the absorption spectrum of Figure 2(A), [Ir(dppm)2(acac)] is This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a belt.

[0173] Emission spectrum 6 has a peak at a longer wavelength (lower energy) than emission spectra 4 and 5. The peak of the emission spectrum 6 is larger than the peaks of the emission spectra 4 and 5. 2(A) and (B), the absorption spectrum is strongly affected by the emission of The emission spectrum that overlaps most with the contributing absorption band is emission spectrum 6. Specifically, the peak of the absorption band (515 nm) in the absorption spectrum and the emission The peak difference in spectrum 6 was 0.02 eV.

[0174] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBNBB is It was found that the spectrum has a peak on the longer wavelength (lower energy) side. Therefore, by mixing 2mDBTPDBq-II and PCBNBB, an exciplex was formed. It was suggested that this is the case.

[0175] The peak in the emission spectrum of the mixed material is the absorption peak of [Ir(dppm)2(acac)]. It was found that there is a large overlap with the absorption band that is thought to strongly contribute to the emission in the spectrum. Therefore, the mixed material of 2mDBTPDBq-II and PCBNBB and [Ir(dpp The light-emitting element using the mixed material (m)2(acac)] has an emission spectrum similar to that of the phosphorescent compound Energy transfer is achieved by utilizing the overlap of the absorption spectrum of Therefore, it is possible to obtain a light-emitting device with high external quantum efficiency. was suggested. [Example]

[0176] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The chemical formulas of the materials used in the previous examples are shown below. .

[0177] [ka]

[0178] The methods for fabricating the light-emitting element 1 and the comparative light-emitting element 2 of this example are described below.

[0179] (Light-emitting element 1) First, indium tin oxide containing silicon oxide (ITSO) is deposited on a glass substrate 1100. The first electrode 1101, which functions as an anode, was formed by a quartz crystal deposition method. The film thickness was 110 nm, and the electrode area was 2 mm x 2 mm.

[0180] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0181] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0182] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about a, 4-phenyl-4'-(9-phenyl fluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and molybdenum oxide ( VI) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of BPAFLP to molybdenum oxide was 4:2 (=BPAFLP:molybdenum oxide). The concentration was adjusted to be 100%.

[0183] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0184] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2( dpm)] was co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. mDBTPDBq-II, PCBNBB and [Ir(mppr-Me)2(dpm)] The weight ratio was 0.8:0.2:0.05 (=2mDBTPDBq-II:PCBNBB:[ The light-emitting layer 1113 was adjusted to have a thickness of 1000 nm. The film thickness was set to 40 nm.

[0185] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 10 nm. A first electron transport layer 1114a was formed.

[0186] Next, bathophenanthroline (abbreviation: BPhen) was applied to the first electron transport layer 1114a. A film was formed to a thickness of 20 nm to form the second electron transport layer 1114b.

[0187] Furthermore, lithium fluoride (LiF) was deposited on the second electron transport layer 1114b to a thickness of 1 nm. An electron injection layer 1115 was formed by evaporation.

[0188] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light-emitting element 1 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0189] (Comparative light-emitting element 2) The light-emitting layer 1113 of the comparative light-emitting element 2 contained 2mDBTPDBq-II and [Ir(mppr- The 2mDBTPDBq-II was formed by co-evaporation of 2mDBTPDBq-II and 2mDBTPDBq-II. and [Ir(mppr-Me)2(dpm)] by weight ratio of 1:0.05 (=2mDBT PDBq-II: [Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 was set to 40 nm. It was made in.

[0190] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0191] The element structures of the thus obtained light-emitting element 1 and comparative light-emitting element 2 are shown in Table 1.

[0192] [Table 1]

[0193] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0194] 3 shows the current density-luminance characteristics of the light-emitting element 1 and the comparative light-emitting element 2. In FIG. is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness characteristics. The characteristics are shown in Figure 4. In Figure 4, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) The luminance-current efficiency characteristics are shown in Figure 5. In Figure 5, the horizontal axis represents luminance (cd / m 2 )of The vertical axis represents the current efficiency (cd / A). The luminance vs. external quantum efficiency characteristics are shown in Figure 6. 6, the horizontal axis is luminance (cd / m 2 ) and the vertical axis indicates the external quantum efficiency (%).

[0195] Furthermore, the luminance of the light-emitting element 1 and the comparative light-emitting element 2 was 1000 cd / m 2 Voltage when near (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A) The power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 2.

[0196] [Table 2]

[0197] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting element 1 and the comparative light-emitting element 2 were , shown in Figure 7. In Figure 7, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 2, 1200 cd / m 2 CIE chromaticity coordinates of light-emitting element 1 at luminance of is (x,y)=(0.56,0.44), and the brightness is 960cd / m 2 Comparison of brightness at The CIE chromaticity coordinates of element 2 were (x, y) = (0.55, 0.44). The light-emitting element 1 and the comparative light-emitting element 2 are derived from [Ir(mppr-Me)2(dpm)]. It was found that orange light emission was obtained.

[0198] As can be seen from Table 2 and FIGS. 3 to 6, the light-emitting element 1 has a current The efficiency, power efficiency, and external quantum efficiency all showed high values.

[0199] In the light-emitting element 1 of this example, 2mDBTPDBq-II and PCBNBB shown in Example 1 were used. and [Ir(mppr-Me)2(dpm)] were used in the light-emitting layer. Compared with the emission spectra of BTPDBq-II and PCBNBB alone, The emission spectrum of the mixture of -II and PCBNBB (emission spectrum of the exciplex) is The absorption spectrum of Ir(mppr-Me)2(dpm) has a large overlap. The light-emitting element 1 transfers energy by utilizing the overlap, and therefore has high energy transfer efficiency. The external quantum efficiency is considered to be higher than that of the comparative light-emitting element 2.

[0200] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that

[0201] Next, reliability tests were performed on the light-emitting element 1 and the comparative light-emitting element 2. The results of the reliability tests are shown in FIG. In FIG. 8, the vertical axis indicates normalized luminance (%) when the initial luminance is 100%, and the horizontal axis indicates normalized luminance (%) when the initial luminance is 100%. The axis indicates the driving time (h) of the element.

[0202] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. The light-emitting element 1 and the comparative light-emitting element 2 were driven.

[0203] The luminance of the comparative light-emitting element 2 after 120 hours was 58% of the initial luminance. The luminance of Light-emitting element 1 after 630 hours was 65% of the initial luminance. It was found that the light-emitting element had a longer life than the comparative light-emitting element 2.

[0204] From the above results, it can be seen that a highly reliable element can be realized by applying one embodiment of the present invention. was shown. [Example]

[0205] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in the above are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0206] The method for fabricating the light-emitting device 3 of this example will be described below.

[0207] (Light-emitting element 3) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0208] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0209] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0210] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about 1000 kJ / cm, BPAFLP and molybdenum oxide (VI ) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of PAFLP to molybdenum oxide was 4:2 (=BPAFLP:molybdenum oxide). The value was adjusted to be 0.

[0211] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0212] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(dppm)2(aca c)] was co-evaporated to form the light-emitting layer 1113 on the hole transport layer 1112. The weight ratio of BTPDBq-II, PCBNBB, and [Ir(dppm)2(acac)] was , 0.8:0.2:0.05(=2mDBTPDBq-II:PCBNBB:[Ir(d The thickness of the light-emitting layer 1113 was adjusted to 40 ppm. nm.

[0213] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 10 nm. A first electron transport layer 1114a was formed.

[0214] Next, a film of BPhen was formed on the first electron transport layer 1114a to a thickness of 20 nm. Then, a second electron transport layer 1114b was formed.

[0215] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0216] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light-emitting element 3 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0217] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0218] The element structure of the light-emitting element 3 obtained as described above is shown in Table 3.

[0219] [Table 3]

[0220] The light emitting element 3 is placed in a glove box with a nitrogen atmosphere so that the light emitting element is not exposed to the atmosphere. After the sealing work was performed as described above, the operating characteristics of the light-emitting element were measured. was carried out at room temperature (atmosphere maintained at 25°C).

[0221] The current density-luminance characteristics of the light-emitting element 3 are shown in FIG. 9. In FIG. 9, the horizontal axis represents the current density (mA / cm2 ) and the vertical axis is luminance (cd / m 2 ) and the voltage-luminance characteristics are shown in Figure 10. In Figure 10, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and luminance - The current efficiency characteristics are shown in Figure 11. In Figure 11, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the voltage The luminance vs. external quantum efficiency characteristics are shown in Figure 12. The horizontal axis is luminance (cd / m 2 ) and the vertical axis indicates the external quantum efficiency (%).

[0222] Furthermore, the luminance of the light-emitting element 3 is 1100 cd / m 2 Voltage (V) and current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W ) and external quantum efficiency (%) are shown in Table 4.

[0223] [Table 4]

[0224] FIG. 13 shows the emission spectrum when a current of 0.1 mA is applied to the light-emitting element 3. In Table 13, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary units). As shown, 1100cd / m 2 The CIE chromaticity coordinates of light-emitting element 3 at a luminance of (x, y) = (0.54, 0.46). From this result, it can be seen that the light-emitting element 3 has an It was found that orange luminescence originating from (acac)] was obtained.

[0225] As can be seen from Table 4 and FIGS. 9 to 12, the light-emitting element 3 has excellent current efficiency, power efficiency, and external The quantum efficiency was high, especially at 1100 cd / m2 External quantum efficiency at a luminance of As mentioned above, the external quantum efficiency is limited to about 25%. However, the results of this study are even higher than that.

[0226] In the light-emitting device of this example, 2mDBTPDBq-II, PCBNBB and and [Ir(dppm)2(acac)] were used in the light-emitting layer. Compared with the emission spectra of DBq-II and PCBNBB alone, 2mDBTPDBq-II The emission spectrum of the mixed material of Ir and PCBNBB (emission spectrum of the exciplex) is [Ir( The absorption spectrum of the light-emitting element of this example overlaps greatly with that of the light-emitting element of the present invention. Since the energy transfer is performed by utilizing the overlap, the energy transfer efficiency is high, and It is believed that an unprecedentedly high external quantum efficiency was obtained.

[0227] In addition, in the results of Example 2, the longest wavelength of the absorption spectrum of the guest material used in the light-emitting element 3 In the absorption band on the longer side, the peak is close to the peak of the emission spectrum and the molar absorption The optical coefficient was large (>5000M -1 ·cm -1 ) From these, it can be seen that the light-emitting element 3 is It is believed that the energy transfer efficiency is particularly high, resulting in an unprecedentedly high external quantum efficiency. .

[0228] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that

[0229] Next, a reliability test was conducted on the light-emitting element 3. The results of the reliability test are shown in FIG. The vertical axis shows the normalized brightness (%) when the initial brightness is 100%, and the horizontal axis shows the driving time of the element. Indicates time (h).

[0230] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. Driven 3.

[0231] After 320 hours, the luminance of the light-emitting element 3 remained at 92% of the initial luminance.

[0232] From the above results, it can be seen that a highly reliable element can be realized by applying one embodiment of the present invention. was shown. [Example]

[0233] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0234] The phosphorescent compound used in this example is [Ir(dppm)2(acac)]. The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in the example is 4-phenyl-4'-(9-phenyl-9H-carbazoline). The compound used in this example is PCBA1BP. The chemical formulas of the materials used are shown below: Note that the chemical formulas of the materials used in the previous examples are omitted.

[0235] [ka]

[0236] <Absorption spectrum> Figure 18(A)(B) shows the dichloromethane of the phosphorescent compound [Ir(dppm)2(acac)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the fluoromethane solution is shown below. The absorption spectrum was measured using an ultraviolet-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were carried out at room temperature. Ta.

[0237] <Emission spectrum> Also, in Figure 18(A)(B), a thin film of the first organic compound, 2mDBTPDBq-II, is shown. Emission spectrum of the second organic compound, PCBA1BP (Emission spectrum 7). Emission spectrum of (Emission spectrum 8), and 2mDBTPDBq-II and PCBA1B The emission spectrum of the thin film of the mixed material of P (Emission spectrum 9) is shown in Figure 18(A). The horizontal axis represents the wavelength (nm) and the vertical axis represents the molar absorption coefficient ε (M -1 ·cm -1 ) and In FIG. 18(B), the horizontal axis represents energy (eV). , the vertical axis is the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary units).

[0238] From the absorption spectrum of Figure 18(A), [Ir(dppm)2(acac)] is It can be seen that there is a broad absorption band near m. This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a convergence.

[0239] Emission spectrum 9 has a peak at a longer wavelength (lower energy) than emission spectra 7 and 8. The peak of the emission spectrum 9 is larger than the peaks of the emission spectra 7 and 8. 18(A) and (B), the absorption spectrum is strongly influenced by the emission of the The emission spectrum that overlaps most with the absorption band that contributes most to the emission is emission spectrum 9. Specifically, the peak of the absorption band (515 nm) in the absorption spectrum and the The peak difference of the optical spectrum 9 was 0.02 eV.

[0240] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBA1BP was It was found that the peak was on the longer wavelength (lower energy) side than the optical spectrum. Therefore, by mixing 2mDBTPDBq-II and PCBA1BP, an exciplex was formed. It was suggested that this would be the case.

[0241] The peak in the emission spectrum of the mixed material is the absorption peak of [Ir(dppm)2(acac)]. It was found that there is a large overlap with the absorption band that is thought to strongly contribute to the emission in the spectrum. Therefore, the mixed material of 2mDBTPDBq-II and PCBA1BP and [Ir(dp The light-emitting element using the mixed material (pm)2(acac)] has the emission spectrum of the phosphorescent compound. Energy transfer is achieved by utilizing the overlap of the absorption spectrum of the substance. Therefore, it is possible to obtain a light-emitting device with high external quantum efficiency. was suggested. [Example]

[0242] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0243] The method for fabricating the light-emitting device 4 of this example will be described below.

[0244] (Light-emitting element 4) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0245] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0246] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0247] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about 1000 kJ / cm, BPAFLP and molybdenum oxide (VI ) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of PAFLP to molybdenum oxide was 4:2 (=BPAFLP:molybdenum oxide). The value was adjusted to be 0.

[0248] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0249] Furthermore, 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)2(ac ac)] was co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. Weight of DBTPDBq-II, PCBA1BP, and [Ir(dppm)2(acac)] The ratio was 0.8:0.2:0.1 (=2mDBTPDBq-II:PCBA1BP:[Ir (dppm)2(acac)]). The film thickness of the light-emitting layer 1113 was adjusted to The thickness was set to 40 nm.

[0250] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 15 nm. A first electron transport layer 1114a was formed.

[0251] Next, BPhen was deposited on the first electron transport layer 1114a to a thickness of 15 nm. Then, a second electron transport layer 1114b was formed.

[0252] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0253] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light-emitting element 4 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0254] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0255] The element structure of the light-emitting element 4 obtained as described above is shown in Table 5.

[0256] [Table 5]

[0257] The light emitting element 4 is placed in a glove box with a nitrogen atmosphere so that the light emitting element is not exposed to the atmosphere. After the sealing work was performed as described above, the operating characteristics of the light-emitting element were measured. was carried out at room temperature (atmosphere maintained at 25°C).

[0258] The current density-luminance characteristics of the light-emitting element 4 are shown in FIG. 19. In FIG. 19, the horizontal axis represents the current density (m A / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and the voltage-luminance characteristics are shown in Figure 20. In Figure 20, the horizontal axis represents voltage (V) and the vertical axis represents luminance (cd / m 2 ) and also represents The luminance-current efficiency characteristics are shown in Figure 21. In Figure 21, the horizontal axis represents luminance (cd / m 2 ) on the vertical axis represents the current efficiency (cd / A). The luminance vs. external quantum efficiency characteristics are shown in Figure 22. In this example, the horizontal axis is luminance (cd / m 2 ) and the vertical axis indicates the external quantum efficiency (%).

[0259] Furthermore, the luminance of the light-emitting element 4 is 1100 cd / m 2 Voltage (V) and current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W ) and external quantum efficiency (%) are shown in Table 6.

[0260] [Table 6]

[0261] FIG. 23 shows the emission spectrum when a current of 0.1 mA is applied to the light-emitting element 4. In 23, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). As shown, 1100cd / m 2 The CIE chromaticity coordinates of light-emitting element 4 at a luminance of (x, y) = (0.57, 0.43). From this result, it can be seen that the light-emitting element 4 has an It was found that orange luminescence originating from (acac)] was obtained.

[0262] As can be seen from Table 6 and FIGS. 19 to 22, the light-emitting element 4 exhibited excellent current efficiency, power efficiency, and external The internal quantum efficiency was high, especially at 1100 cd / m 2 External quantum at the brightness of The efficiency was extremely high at 31%. As mentioned earlier, the limit of external quantum efficiency is 25%. However, the results of this study are even better than that.

[0263] In the light-emitting device of this example, 2mDBTPDBq-II and PCBA1BP shown in Example 5 were used. and [Ir(dppm)2(acac)] were used in the light-emitting layer. Compared with the emission spectra of PDBq-II and PCBA1BP alone, The emission spectrum of the mixture of II and PCBA1BP (emission spectrum of the exciplex) is The absorption spectrum of the compound Ir(dppm)2(acac) is significantly overlapped with that of the compound Ir(dppm)2(acac). Optical elements utilize this overlap to transfer energy, resulting in high energy transfer efficiency. It is believed that an unprecedentedly high external quantum efficiency was achieved.

[0264] In addition, in the results of Example 5, the longest wavelength of the absorption spectrum of the guest material used in the light-emitting element 4 In the absorption band on the longer side, the peak is close to the peak of the emission spectrum and the molar absorption The optical coefficient was large (>5000M -1 ·cm -1 ) From these, it can be seen that the light-emitting element 4 is It is believed that the energy transfer efficiency is particularly high, resulting in an unprecedentedly high external quantum efficiency. .

[0265] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that

[0266] Next, a reliability test was conducted on the light-emitting element 4. The results of the reliability test are shown in FIG. The vertical axis shows the normalized brightness (%) when the initial brightness is 100%, and the horizontal axis shows the driving time of the element. Indicates time (h).

[0267] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. Driven 4.

[0268] After 170 hours, the luminance of the light-emitting element 4 remained at 95% of the initial luminance.

[0269] From the above results, it can be seen that a highly reliable element can be realized by applying one embodiment of the present invention. was shown. [Example]

[0270] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0271] The phosphorescent compound used in this example is [Ir(dppm)2(acac)]. The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in the example is 4,4'-bis[N-(1-naphthyl)-N-phenyl The chemical formula of the material used in this example is shown below. The chemical formulas of the materials used in the previous examples are omitted.

[0272] [ka]

[0273] <Absorption spectrum> Figure 26(A)(B) shows the dichloromethane of the phosphorescent compound [Ir(dppm)2(acac)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the fluoromethane solution is shown below. The absorption spectrum was measured using an ultraviolet-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were carried out at room temperature. Ta.

[0274] <Emission spectrum> Also, in Figure 26(A)(B), a thin film of the first organic compound, 2mDBTPDBq-II, is shown. The emission spectrum of 2mDBTPDBq-II (Emission spectrum 10) and the mixture of 2mDBTPDBq-II and NPB The emission spectrum (emission spectrum 11) of the thin film of the composite material is shown in FIG. The horizontal axis indicates the wavelength (nm), and the vertical axis indicates the molar extinction coefficient ε (M -1 ·cm -1 ) and luminous intensity In FIG. 26(B), the horizontal axis represents energy (eV), and the vertical axis represents The axis is the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary units).

[0275] From the absorption spectrum of Figure 26(A), [Ir(dppm)2(acac)] is It can be seen that there is a broad absorption band near m. This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a convergence.

[0276] Emission spectrum 11 has a peak at a longer wavelength (lower energy) than emission spectrum 10. The peak of the emission spectrum 11 is smaller than the peak of the emission spectrum 10. The emission spectrum of the second organic compound, NPB, is It is known that the peak of the emission spectrum is around 430 nm. The emission spectrum of 11 has a peak at a longer wavelength (lower energy) side than that of NPB. The peak of the emission spectrum 11 is smaller than that of NPB. From the above, it can be said that the emission of the absorption spectrum is close to the absorption band. The emission spectrum that overlaps most with the absorption band that strongly contributes to the Specifically, it was found that the peak of the absorption band in the absorption spectrum (515 nm The difference between the peak of the luminescence spectrum 11 and that of the luminescence spectrum 12 was 0.09 eV.

[0277] The emission spectrum of the mixture of 2mDBTPDBq-II and NPB is It was found that the peak is on the longer wavelength (lower energy) side than that of the ion beam. It is suggested that exciplexes are formed by mixing 2mDBTPDBq-II with NPB. was done.

[0278] The peak in the emission spectrum of the mixed material is the absorption peak of [Ir(dppm)2(acac)]. It was found that there is a large overlap with the absorption band that is thought to strongly contribute to the emission in the spectrum. Therefore, the mixed material of 2mDBTPDBq-II and NPB and [Ir(dppm)2 The light-emitting element using (acac)] exhibits a characteristic that the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound are Energy transfer is performed using the overlap of the spectrum, resulting in high energy transfer efficiency. Therefore, it is suggested that a light-emitting device with high external quantum efficiency can be obtained. It was. [Example]

[0279] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The chemical formulas of the materials used in the previous examples are shown below. .

[0280] [ka]

[0281] The methods for fabricating the light-emitting element 5 of this example and the comparative light-emitting element 6 are described below.

[0282] (Light-emitting element 5) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0283] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0284] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0285] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4P After the pressure was reduced to about 1000 kJ / cm, 4,4',4''-(1,3,5-benzyl alcohol) was added to the first electrode 1101. DBT3P-II) and molybdenum oxide The hole injection layer 1111 was formed by co-evaporation of ZnO and Zn(VI). The weight ratio of DBT3P-II to molybdenum oxide was 4:2 (=DBT3P- II: molybdenum oxide).

[0286] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0287] Furthermore, 2mDBTPDBq-II, NPB, and [Ir(dppm)2(acac)] The light-emitting layer 1113 was formed on the hole transport layer 1112 by co-evaporation. The weight ratio of Bq-II, NPB, and [Ir(dppm)2(acac)] was 0.8:0. 2:0.05(=2mDBTPDBq-II:NPB:[Ir(dppm)2(acac )) The thickness of the light-emitting layer 1113 was set to 40 nm.

[0288] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 10 nm. A first electron transport layer 1114a was formed.

[0289] Next, a film of BPhen was formed on the first electron transport layer 1114a to a thickness of 20 nm. Then, a second electron transport layer 1114b was formed.

[0290] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0291] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light-emitting element 5 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0292] (Comparative light-emitting element 6) The light-emitting layer 1113 of the comparative light-emitting element 6 contained 2mDBTPDBq-II and [Ir(dppm) 2(acac)] was co-evaporated. The weight ratio of [Ir(dppm)2(acac)] was 1:0.05 (=2mDBTPDBq -II:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 was 40 nm.

[0293] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0294] Table 7 shows the element structures of the thus obtained light-emitting element 5 and comparative light-emitting element 6.

[0295] [Table 7]

[0296] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0297] FIG. 27 shows the current density-luminance characteristics of the light-emitting element 5 and the comparative light-emitting element 6. In FIG. The horizontal axis is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness The brightness characteristics are shown in Figure 28. In Figure 28, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and the luminance-current efficiency characteristics are shown in Figure 29. In Figure 29, the horizontal axis represents the luminance (c d / m 2 The vertical axis represents the current efficiency (cd / A), and the vertical axis represents the luminance vs. external quantum efficiency characteristics. 30. In FIG. 30, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the external quantum efficiency (% ) is shown.

[0298] Furthermore, the luminance of the light-emitting element 5 and the comparative light-emitting element 6 was 1000 cd / m 2 Voltage when near (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A) The power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 8.

[0299] [Table 8]

[0300] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting element 5 and the comparative light-emitting element 6 were 31. In FIG. 31, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 8, 1100 cd / m 2 CIE chromaticity of light-emitting element 5 at luminance The coordinates are (x,y)=(0.57,0.43), and the brightness is 830cd / m 2 Comparison at brightness of The CIE chromaticity coordinates of the light-emitting element 6 were (x, y) = (0.56, 0.44). Therefore, the light-emitting element 5 and the comparative light-emitting element 6 have a luminescence element derived from [Ir(dppm)2(acac)]. It was found that orange light emission was obtained.

[0301] As can be seen from Table 8 and FIGS. 27 to 30, the light-emitting element 5 has the following characteristics compared to the comparative light-emitting element 6: The current efficiency, power efficiency, and external quantum efficiency all showed high values.

[0302] The light-emitting device 5 was fabricated using 2mDBTPDBq-II, NPB, and [Ir(dpp m)2(acac)] was used in the light-emitting layer. The emission spectrum of the mixture of 2mDBTPDBq-II and NPB is The emission spectrum of the exciplex is the absorption spectrum of [Ir(dppm)2(acac)]. There is a large overlap with the absorption band that is thought to strongly contribute to light emission in the spectrum. Since the energy transfer is performed by utilizing the overlap, the energy transfer efficiency is high and the It is believed that the external quantum efficiency is higher than that of the optical element 6.

[0303] In addition, in the results of Example 7, the phosphorescent compound used in the light-emitting element 5 has the longest absorption spectrum. In the absorption band on the wavelength side, the peak is close to the peak of the emission spectrum, and the mole fraction of the peak The extinction coefficient was large (>5000 M -1 ·cm -1 ) From these, it can be seen that the light-emitting element 5 is The energy transfer efficiency is particularly high, which is thought to be the reason why the external quantum efficiency was higher than ever before. do.

[0304] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that [Example]

[0305] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0306] The phosphorescent compound used in this example is bis(2,3,5-triphenylpyrazinato) (dipyridine). Valoylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]) The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is NPB. The chemical formula is shown below: Note that the chemical formulas of the materials used in the previous examples are omitted.

[0307] [ka]

[0308] <Absorption spectrum> Figure 32(A)(B) shows the dichloromethane of the phosphorescent compound [Ir(tppr)2(dpm)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the methane solution is shown below. The spectrum was measured using an ultraviolet-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.094 mmol / L) was placed in a quartz cell and measurements were performed at room temperature. .

[0309] <Emission spectrum> Also, in Figure 32(A)(B), a thin film of the first organic compound, 2mDBTPDBq-II, is shown. The emission spectrum of 2mDBTPDBq-II (Emission spectrum 12) and the mixture of 2mDBTPDBq-II and NPB The emission spectrum of the thin film of the composite material (emission spectrum 13) is shown in Figure 32(A). The horizontal axis indicates the wavelength (nm), and the vertical axis indicates the molar extinction coefficient ε (M -1 ·cm -1 ) and luminous intensity In FIG. 32(B), the horizontal axis represents energy (eV), and the vertical axis represents The axis is the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary units).

[0310] From the absorption spectrum of Figure 32(A), [Ir(tppr)2(dpm)] is This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a belt.

[0311] Emission spectrum 13 has a peak at a longer wavelength (lower energy) than emission spectrum 12. The peak of the emission spectrum 13 is smaller than the peak of the emission spectrum 12. The emission spectrum of the second organic compound, NPB, is It is known that the peak of the emission spectrum is around 430 nm. The emission spectrum of 13 has a peak at a longer wavelength (lower energy) than that of NPB. The peak of the emission spectrum 13 is smaller than that of NPB. From the above, it can be said that the emission of the absorption spectrum is close to the absorption band. The emission spectrum that overlaps most with the absorption band that strongly contributes to the emission spectrum is emission spectrum 13. Specifically, it was found that the peak of the absorption band in the absorption spectrum (530 nm The difference between the peak of the emission spectrum (shoulder peak near the center) and the peak of the emission spectrum 13 was 0.01 eV.

[0312] The emission spectrum of the mixture of 2mDBTPDBq-II and NPB is It was found that the peak is on the longer wavelength (lower energy) side than that of the ion beam. It is suggested that exciplexes are formed by mixing 2mDBTPDBq-II with NPB. was done.

[0313] The peak in the emission spectrum of the mixed material is the absorption spectrum of [Ir(tppr)2(dpm)]. It was found that there is a large overlap with the absorption bands that are thought to strongly contribute to the luminescence in the Therefore, the mixed material of 2mDBTPDBq-II and NPB and [Ir(tppr)2( dpm)], the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound Energy transfer is achieved by utilizing the overlap with the vector, so the energy transfer efficiency is high. Therefore, it was suggested that a light-emitting device with high external quantum efficiency could be obtained. . [Example]

[0314] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in the above are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0315] The methods for fabricating the light-emitting element 7 of this example and the comparative light-emitting element 8 are described below.

[0316] (Light emitting element 7) The light-emitting layer 1113 of the light-emitting element 7 was made of 2mDBTPDBq-II, NPB, and [Ir(tpp r)2(dpm)] was co-evaporated. The weight ratio of NPB and [Ir(tppr)2(dpm)] was 0.8:0.2:0.05 ( =2mDBTPDBq-II:NPB:[Ir(tppr)2(dpm)]) The thickness of the light-emitting layer 1113 was adjusted to 40 nm. The light-emitting device was fabricated in the same manner as in Example 8.

[0317] (Comparative light-emitting element 8) The light-emitting layer 1113 of the comparative light-emitting element 8 contained 2mDBTPDBq-II and [Ir(tppr) 2(dpm)] was co-evaporated. The weight ratio of Ir(tppr)2(dpm) was 1:0.05 (=2mDBTPDBq-I I:[Ir(tppr)2(dpm)]). The thickness of the light-emitting layer 1113 was set to 40 nm. It was made.

[0318] Table 9 shows the element structures of the thus obtained light-emitting element 7 and comparative light-emitting element 8.

[0319] [Table 9]

[0320] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0321] FIG. 33 shows the current density-luminance characteristics of the light-emitting element 7 and the comparative light-emitting element 8. In FIG. The horizontal axis is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness The brightness characteristics are shown in Figure 34. In Figure 34, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and the luminance-current efficiency characteristics are shown in Figure 35. In Figure 35, the horizontal axis represents the luminance (c d / m 2 The vertical axis represents the current efficiency (cd / A), and the vertical axis represents the luminance vs. external quantum efficiency characteristics. 36. In FIG. 36, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the external quantum efficiency (% ) is shown.

[0322] Furthermore, the luminance of the light-emitting element 7 and the comparative light-emitting element 8 was 1000 cd / m 2 Voltage when near (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A) The power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 10.

[0323] [Table 10]

[0324] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting element 7 and the comparative light-emitting element 8 were 37. In FIG. 37, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 10, 1100 cd / m 2 CIE color of light-emitting element 7 at luminance of The degree coordinates are (x,y)=(0.66,0.34), and the angle is 1000cd / m 2 At a brightness of The CIE chromaticity coordinates of the comparative light-emitting element 8 were (x, y) = (0.66, 0.34). From the results, it can be seen that the light-emitting element 7 and the comparative light-emitting element 8 are derived from [Ir(tppr)2(dpm)]. It was found that red light emission was obtained.

[0325] As can be seen from Table 10 and FIGS. 33 to 36, the light-emitting element 7 exhibited a higher The current efficiency, power efficiency, and external quantum efficiency all showed high values.

[0326] In the light-emitting device 7, 2mDBTPDBq-II, NPB, and [Ir(tp pr)2(dpm)] was used in the light-emitting layer. The emission spectrum of the mixture of 2mDBTPDBq-II and NPB is The emission spectrum of the exciplex is the absorption spectrum of [Ir(tppr)2(dpm)]. The overlap with the absorption band that is thought to strongly contribute to light emission in the EL element is large. Since the energy transfer is performed by utilizing this overlap, the energy transfer efficiency is high and the comparative luminescence It is believed that the external quantum efficiency is higher than that of Device 8.

[0327] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that

[0328] Next, reliability tests were performed on the light-emitting element 7 and the comparative light-emitting element 8. The results of the reliability tests are shown in FIG. In FIG. 38, the vertical axis indicates normalized luminance (%) when the initial luminance is 100%. The horizontal axis indicates the driving time (h) of the element.

[0329] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. The light-emitting element 7 and the comparative light-emitting element 8 were driven.

[0330] The luminance of the comparative light-emitting element 8 after 97 hours was 63% of the initial luminance. The luminance after 98 hours was 87% of the initial luminance. It was found that the element had a longer life than the comparative light emitting element 8.

[0331] From the above results, it can be seen that a highly reliable element can be realized by applying one embodiment of the present invention. was shown. [Example]

[0332] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0333] The phosphorescent compound used in this example is (acetylacetonato)bis(6-methyl-4-phenyl)- Nylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)] The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is PCBA1BP and 4-(1-naphthyl)- There are two types: α-4'-phenyltriphenylamine (abbreviated as αNBA1BP) and α-4'-phenyltriphenylamine (abbreviated as αNBA1BP). The chemical formulas of the materials used in the examples are shown below. Note that the chemical formulas of the materials used in the previous examples are omitted. Abbreviated.

[0334] [ka]

[0335] <Absorption spectrum> Figure 39(A)(B) shows the dichloromethane of the phosphorescent compound [Ir(mppm)2(acac)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the fluoromethane solution is shown below. The absorption spectrum was measured using an ultraviolet-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). The dichloromethane solution (0.10 mmol / L) was placed in a quartz cell and measurements were carried out at room temperature. .

[0336] <Emission spectrum> Also, in Figure 39(A)(B), a thin film of the first organic compound, 2mDBTPDBq-II, is shown. The emission spectrum of the second organic compound, PCBA1BP (Emission spectrum 14), The emission spectrum of the film (Emission spectrum 15), the second organic compound, αNBA1BP Emission spectra of thin films (Emission spectrum 16), 2mDBTPDBq-II and PCBA1 Emission spectra of thin films of BP mixed materials (Emission spectrum 17), and 2mDBTPDB The emission spectrum of the thin film of the mixed material of q-II and αNBA1BP (Emission spectrum 18) In FIG. 39(A), the horizontal axis represents wavelength (nm) and the vertical axis represents molar absorption coefficient ε ( M -1 ·cm -1 ) and luminescence intensity (arbitrary unit). In FIG. 39(B), the horizontal axis represents The vertical axis represents the molar absorption coefficient ε (M -1 ·cm -1 ) and emission intensity (arbitrary unit).

[0337] From the absorption spectrum of Figure 39(A), [Ir(mppm)2(acac)] is It can be seen that there is a broad absorption band near m. This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a convergence.

[0338] Emission spectrum of the mixture of 2mDBTPDBq-II and PCBA1BP (Emission spectrum 17), and the emission spectra of the mixture of 2mDBTPDBq-II and αNBA1BP (Emission spectrum 18) has a longer wavelength (lower energy) than the emission spectrum of each element. It was found that there was a peak on the - side. It was suggested that mixing CBA1BP with 2mD It was shown that exciplexes were formed by mixing BTPDBq-II and αNBA1BP. was suggested.

[0339] The emission spectrum peak of the above mixed material is the absorption peak of [Ir(mppm)2(acac)] It was found that there was a large overlap with the absorption band that is thought to strongly contribute to the emission in the spectrum. Therefore, the mixed material of 2mDBTPDBq-II and PCBA1BP and [Ir(m ppm)2(acac)] and 2mDBTPDBq-II and αNBA1 The light-emitting device using the mixed material of BP and [Ir(mppm)2(acac)] is The overlap between the emission spectrum of the material and the absorption spectrum of the phosphorescent compound is used to Therefore, it is suggested that the energy transfer efficiency is high. It was suggested that a highly efficient light-emitting device could be obtained.

[0340] Here, the emission spectrum 18 is on the shorter wavelength (higher energy) side than the emission spectrum 17. The peak of the emission spectrum 18 is the same as the peak of the emission spectrum 17. Specifically, the absorption band in the absorption spectrum is closer to the absorption band in the The difference between the peak of the band (shoulder peak around 490 nm) and the peak of the emission spectrum 17 is 0.15 eV, and the peak of the absorption band in the absorption spectrum (short wave around 490 nm) The difference between the peak of the luminescence spectrum (below) and the peak of the emission spectrum 18 was 0.01 eV.

[0341] The difference between the peaks of emission spectrum 17 and 18 is the difference between PCBA1BP and αNBA1 This is thought to be due to the difference in the HOMO level of PCBA1BP. The HOMO level of αNBA1BP is -5.52 eV, while the O level is -5.43 eV. V (both values ​​were calculated by cyclic voltammetry (CV) measurement). Compared to CBA1BP, αNBA1BP has a lower (deeper) HOMO level, resulting in a The peak of the emission spectrum 18 is thought to be at a shorter wavelength (higher energy) than that of the emission spectrum 17. can be done. [Example]

[0342] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in the above are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0343] The method for fabricating the light-emitting elements 9 and 10 of this example will be described below.

[0344] (Light emitting element 9) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0345] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0346] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0347] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about 1000 kJ / cm, BPAFLP and molybdenum oxide (VI ) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of PAFLP to molybdenum oxide was 4:2 (=BPAFLP:molybdenum oxide). The value was adjusted to be 0.

[0348] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0349] Furthermore, 2mDBTPDBq-II, PCBA1BP, and [Ir(mppm)2(aca c)] was co-evaporated to form the light-emitting layer 1113 on the hole transport layer 1112. Weight ratio of BTPDBq-II, PCBA1BP, and [Ir(mppm)2(acac)] is 0.8:0.2:0.05 (=2mDBTPDBq-II:PCBA1BP:[Ir (mppm)2(acac)]). The film thickness of the light-emitting layer 1113 was adjusted to The thickness was set to 40 nm.

[0350] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 10 nm. A first electron transport layer 1114a was formed.

[0351] Next, a film of BPhen was formed on the first electron transport layer 1114a to a thickness of 20 nm. Then, a second electron transport layer 1114b was formed.

[0352] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0353] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light-emitting element 9 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0354] (Light-emitting element 10) The light-emitting layer 1113 of the light-emitting element 10 contains 2mDBTPDBq-II, αNBA1BP, and [I r(mppm)2(acac)] was co-evaporated. The weight ratio of Bq-II, αNBA1BP, and [Ir(mppm)2(acac)] was 0. 8:0.2:0.05(=2mDBTPDBq-II:αNBA1BP:[Ir(mpp The thickness of the light-emitting layer 1113 was adjusted to 40 nm. The other components than the light-emitting layer 1113 were fabricated in the same manner as in the light-emitting element 9.

[0355] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0356] Table 11 shows the element structures of the light-emitting elements 9 and 10 obtained as described above.

[0357] [Table 11]

[0358] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0359] FIG. 40 shows the current density-luminance characteristics of the light-emitting elements 9 and 10. In FIG. The axis represents the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2) and voltage-brightness The characteristics are shown in Figure 41. In Figure 41, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) The luminance-current efficiency characteristics are shown in Figure 42. In Figure 42, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis represents the current efficiency (cd / A). The luminance vs. external quantum efficiency characteristics are shown in Figure 4 3. In FIG. 43, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the external quantum efficiency (%). Shows.

[0360] Furthermore, the luminance of the light-emitting element 9 and the light-emitting element 10 is 1000 cd / m 2 The voltage when V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A), Table 12 shows the power efficiency (lm / W) and external quantum efficiency (%).

[0361] [Table 12]

[0362] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting elements 9 and 10 were This is shown in Figure 44. In Figure 44, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 12, 1100 cd / m 2 CIE chromaticity of light-emitting element 9 at luminance The coordinates are (x,y)=(0.43,0.56), and the brightness is 860cd / m 2 Light emission at brightness of The CIE chromaticity coordinates of element 10 were (x, y) = (0.43, 0.56). Therefore, the light-emitting elements 9 and 10 are made of a yellow light-emitting element derived from [Ir(mppm)2(acac)]. It was found that green light was obtained.

[0363] As can be seen from Table 12 and FIGS. 40 to 43, the light-emitting elements 9 and 10 exhibited a high current efficiency. The efficiency, power efficiency, and external quantum efficiency all showed high values.

[0364] The light-emitting elements 9 and 10 were made of PCBA1BP or αNBA1BP shown in Example 11. , 2mDBTPDBq-II, and [Ir(mppm)2(acac)] as the light-emitting layer. From Example 11, 2mDBTPDBq-II and PCBA1BP or αNBA1 were used. The emission spectrum of the mixed material with BP (emission spectrum of the exciplex) is [Ir(mppm )2(acac)], which is thought to contribute strongly to the emission. The light-emitting element 9 and the light-emitting element 10 utilize this overlap to transfer energy. Therefore, it is thought that the energy transfer efficiency is high and the external quantum efficiency is high.

[0365] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that

[0366] Next, reliability tests were conducted on the light-emitting elements 9 and 10. The results of the reliability tests are shown in FIG. In FIG. 45, the vertical axis indicates normalized brightness (%) when the initial brightness is 100%, The horizontal axis indicates the driving time (h) of the element.

[0367] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. The light-emitting element 9 and the light-emitting element 10 were driven.

[0368] The luminance of the light-emitting element 9 after 260 hours was 74% of the initial luminance. The luminance after 260 hours was 75% of the initial luminance. The light-emitting device 10 was found to have a long life.

[0369] From the above results, it can be seen that a highly reliable element can be realized by applying one embodiment of the present invention. was shown. [Example]

[0370] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0371] The phosphorescent compound used in this example is (acetylacetonato)bis(6-tert-butyl -4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2 (acac)]). The first organic compound used in this example is 2mDBTPD The second organic compound used in this example is NPB and 2,7-bis(2,7-biphenyl). Spiro-9,9'-[N-(4-diphenylaminophenyl)-N-phenylamino] The chemical formula of the material used in this example is The chemical formulas of the materials used in the previous examples are omitted below.

[0372] [ka]

[0373] <Absorption spectrum> Figure 46(A)(B) shows the dimer of the phosphorescent compound [Ir(tBuppm)2(acac)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the chloromethane solution is shown below. The absorption spectrum was measured using a UV-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were taken at room temperature. went.

[0374] <Emission spectrum> Also, in Figure 46(A)(B), a thin film of the first organic compound, 2mDBTPDBq-II, is shown. Emission spectrum of the second organic compound, DPA2SF (Emission spectrum 19), Emission spectrum of (Emission spectrum 20), 2mDBTPDBq-II and DPA2SF Emission spectra of thin films of mixed materials (Emission spectrum 21) and 2mDBTPDBq-II The emission spectrum of the thin film of the mixed material of ZnO and NPB (emission spectrum 22) is shown in Figure 46(A). ), the horizontal axis represents wavelength (nm) and the vertical axis represents molar absorption coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary units). In FIG. 46(B), the horizontal axis represents energy (eV ), and the vertical axis represents the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary unit) vinegar.

[0375] From the absorption spectrum of Figure 46(A), [Ir(tBuppm)2(acac)] is It can be seen that there is a broad absorption band around 0 nm. This absorption band strongly contributes to the emission. It is thought that this is an absorption band.

[0376] Emission spectrum of the mixture of 2mDBTPDBq-II and DPA2SF (Emission spectrum 21) has a peak on the longer wavelength (lower energy) side than the emission spectrum of the single substance. This indicates that mixing 2mDBTPDBq-II and DPA2SF , suggesting that an exciplex is formed.

[0377] In addition, the peak of the emission spectrum of NPB alone is known to be around 430 nm. From Figure 46(A), the emission spectrum of the mixed material of 2mDBTPDBq-II and NPB is The emission spectrum (22) has a peak on the longer wavelength side than 430 nm, It was suggested that exciplexes were formed by mixing BTPDBq-II with NPB. .

[0378] The emission spectrum of the above mixed material has a peak of [Ir(tBuppm)2(acac)] The absorption spectrum has a large overlap with the absorption band that is thought to strongly contribute to the emission. Therefore, the mixed material of 2mDBTPDBq-II and DPA2SF and [Ir( tBuppm)2(acac)] and 2mDBTPDBq-II and NP The light-emitting device using the mixed material of B and [Ir(tBuppm)2(acac)] is The overlap between the emission spectrum of the composite material and the absorption spectrum of the phosphorescent compound is used to Therefore, it is suggested that the energy transfer efficiency is high. It was suggested that a light-emitting device with high photon efficiency could be obtained.

[0379] Here, the emission spectrum 22 is on the shorter wavelength (higher energy) side than the emission spectrum 21. The peak of the emission spectrum 22 is the same as the peak of the emission spectrum 21. As a result, in Figure 46, the absorption spectrum The emission spectrum that overlaps most with the absorption band that strongly contributes to the emission of the nucleon is Specifically, the peak of the absorption band in the absorption spectrum The difference between the peak of the emission spectrum 21 and that of the absorption spectrum 22 is 0.39 eV. The difference between the peak of the absorption band and the peak of the emission spectrum 22 was 0.19 eV.

[0380] The difference between the peaks of the emission spectrum 21 and the emission spectrum 22 is the difference between the peaks of the second organic compound and the peaks of the second organic compound. This is thought to be due to the difference in the HOMO levels of DPA2SF and NPB. The HOMO level of A2SF is -5.09 eV, while the HOMO level of NPB is -5 The value was 0.38 eV (both values ​​were calculated by CV measurement). Since the HOMO level of PB is low (deep), the peak of the emission spectrum 22 is It is thought that the wavelength is shorter (higher energy) than that of Ion 21.

[0381] From the above, it is clear that the mixed material of 2mDBTPDBq-II and NPB and [Ir(tBup The light-emitting devices using the [pm)2(acac)] are 2mDBTPDBq-II and DPA2SF Compared with the light-emitting device using the mixed material [Ir(tBuppm)2(acac)], Taking advantage of the greater overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound, This suggests that the energy transfer efficiency is higher because the energy is transferred using a fluorine-containing compound. Therefore, it was suggested that a light-emitting device with higher external quantum efficiency could be obtained.

[0382] Furthermore, from this example, it was found that the second organic compound could be changed without changing the first organic compound. By simply using the compound, the emission spectrum of the mixed material of the first organic compound and the second organic compound and the phosphorescence It was found that the overlap of the absorption spectra of the compounds can be increased. When changing the emission color (the position of the absorption band that strongly contributes to the emission of the absorption spectrum), However, by simply changing the second organic compound, it is possible to obtain a combination that increases the overlap. It was suggested that a light-emitting device with high external quantum efficiency and long life could be obtained. [Example]

[0383] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in the above are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0384] The method for fabricating the light-emitting elements 11 and 12 of this example will be described below.

[0385] (Light emitting element 11) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0386] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0387] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0388] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about a, DBT3P-II and molybdenum oxide ( VI) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of DBT3P-II to molybdenum oxide was 4:2 (=DBT3P-II: The temperature was adjusted to be molybdenum oxide.

[0389] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0390] Furthermore, 2mDBTPDBq-II, DPA2SF and [Ir(tBuppm)2(ac ac)] was co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. DBTPDBq-II, DPA2SF and [Ir(tBuppm)2(acac)] The ratio was 0.8:0.2:0.05 (=2mDBTPDBq-II:DPA2SF:[I r(tBuppm)2(acac)]). The film thickness was set to 40 nm.

[0391] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 10 nm. A first electron transport layer 1114a was formed.

[0392] Next, a film of BPhen was formed on the first electron transport layer 1114a to a thickness of 20 nm. Then, a second electron transport layer 1114b was formed.

[0393] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0394] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light emitting element 11 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0395] (Light emitting element 12) The light-emitting layer 1113 of the light-emitting element 12 contains 2mDBTPDBq-II, NPB, and [Ir(tB uppm)2(acac)]. The weight ratio of I, NPB, and [Ir(tBuppm)2(acac)] was 0.8:0. 2:0.05(=2mDBTPDBq-II:NPB:[Ir(tBuppm)2(ac The thickness of the light-emitting layer 1113 was adjusted to 40 nm. The layers other than the layer 1113 were fabricated in the same manner as in the light-emitting element 11.

[0396] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0397] Table 13 shows the element structures of the thus obtained light-emitting elements 11 and 12.

[0398] [Table 13]

[0399] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0400] FIG. 47 shows the current density-luminance characteristics of the light-emitting elements 11 and 12. In FIG. The horizontal axis is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness The brightness characteristics are shown in Figure 48. In Figure 48, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and the luminance-current efficiency characteristics are shown in Figure 49. In Figure 49, the horizontal axis represents the luminance (c d / m 2 The vertical axis represents the current efficiency (cd / A), and the vertical axis represents the luminance vs. external quantum efficiency characteristics. 50. In FIG. 50, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the external quantum efficiency (% ) is shown.

[0401] Furthermore, the luminance of the light-emitting element 11 and the light-emitting element 12 is 1000 cd / m 2 Voltage when near (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A) The power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 14.

[0402] [Table 14]

[0403] The emission spectra when a current of 0.1 mA is applied to the light-emitting elements 11 and 12 are shown in Table 1. , shown in Figure 51. In Figure 51, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 14, 890 cd / m 2 CIE color of light emitting element 11 at luminance The degree coordinates are (x,y)=(0.43,0.56), and the brightness is 820cd / m 2 At the brightness of The CIE chromaticity coordinates of the optical element 12 were (x, y) = (0.42, 0.57). Therefore, the light-emitting elements 11 and 12 are derived from [Ir(tBuppm)2(acac)]. It was found that yellow-green luminescence was obtained.

[0404] As can be seen from Table 14 and FIGS. 47 to 50, the light-emitting elements 11 and 12 exhibited a current The efficiency, power efficiency, and external quantum efficiency all showed high values.

[0405] The light-emitting elements 11 and 12 were prepared by mixing DPA2SF or NPB as shown in Example 13 with 2m DBTPDBq-II and [Ir(tBuppm)2(acac)] were used for the light-emitting layer. From Example 13, the mixed material of 2mDBTPDBq-II and DPA2SF or NPB The emission spectrum of the exciplex is [Ir(tBuppm)2(aca c)], there is a large overlap with the absorption band that is thought to strongly contribute to the emission. The light emitting element 11 and the light emitting element 12 transfer energy by utilizing the overlap. It is believed that the energy transfer efficiency is high and the external quantum efficiency is high. The emission spectrum of the mixed material of Bq-II and NPB is Compared to the emission spectrum of the 2SF mixed material, the overlap with the absorption band is large. The light-emitting element 12 utilizes the large overlap to transfer energy, and therefore, the light-emitting element 11 It is considered that the energy transfer efficiency is higher and the external quantum efficiency is higher than that of Example 1. By referring to the results of 3, the energy value of the peak in the emission spectrum of the exciplex can be calculated. The difference between the energy value of the peak of the absorption band on the lowest energy side of the absorption spectrum is 0 It can be seen that it is preferable for the difference to be within 0.3 eV.

[0406] In this example, the first organic compound (corresponding to 2mDBTPDBq-II) was not changed. By simply changing the second organic compound (using NPB instead of DPA2SF), Furthermore, a light-emitting device with high external quantum efficiency was obtained.

[0407] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that [Example]

[0408] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0409] The phosphorescent compound used in this example is [Ir(mppr-Me)2(dpm)]. The first organic compound used in this example is 2mDBTPDBq-II and 2-[4-( Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: DBTBIm-II). The compound is 4,4',4''-tris[N-(1-naphthyl)-N-phenylamino]triphenyl The chemical formula of the material used in this example is as follows: The chemical formulas of the materials used in the previous examples are omitted.

[0410] [ka]

[0411] <Absorption spectrum> Figure 52(A)(B) shows the dimer of the phosphorescent compound [Ir(mppr-Me)2(dpm)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the chloromethane solution is shown below. The absorption spectrum was measured using a UV-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were taken at room temperature. went.

[0412] <Emission spectrum> Also, in Figure 52(A)(B), a thin film of the first organic compound, 2mDBTPDBq-II, is shown. The emission spectrum of the first organic compound, DBTBIm-II (Emission spectrum 23) The emission spectrum of the thin film of the second organic compound, 1'-TNA (emission spectrum 24) Emission spectra of thin films of TA (Emission spectrum 25), 2mDBTPDBq-II and 1' Emission spectra of thin films of the mixed material of -TNATA (Emission spectrum 26), and DBTB Emission spectrum of the thin film of the mixture of Im-II and 1'-TNATA (Emission spectrum 27 In FIG. 52(A), the horizontal axis represents wavelength (nm) and the vertical axis represents molar absorption coefficient. ε(M -1 ·cm -1 ) and luminescence intensity (arbitrary unit). indicates energy (eV), and the vertical axis indicates the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence Indicates intensity (arbitrary unit).

[0413] From the absorption spectrum of Figure 52(A), [Ir(mppr-Me)2(dpm)] is It can be seen that there is a broad absorption band around 0 nm. This absorption band strongly contributes to the emission. It is thought that this is an absorption band.

[0414] Emission spectrum of the mixture of 2mDBTPDBq-II and 1'-TNATA (Emission spectrum 26), and the emission spectrum of the mixture of DBTBIm-II and 1'-TNATA ( The emission spectrum 27) has longer wavelengths (lower energy) than the emission spectrum of each element. ) side. This indicates that 2mDBTPDBq-II and 1' It was suggested that mixing DBT with TNATA would result in the formation of an exciplex. It was suggested that the exciplex was formed by mixing BIm-II with 1'-TNATA. It was.

[0415] The emission spectrum of the above mixed material has a peak of [Ir(mppr-Me)2(dpm)]. The absorption spectrum has a large overlap with the absorption band that is thought to strongly contribute to the emission. Therefore, the mixture of 2mDBTPDBq-II and 1'-TNATA and [I r(mppr-Me)2(dpm)] and DBTBIm-II and 1'- Light-emitting devices using TNATA mixed materials and [Ir(mppr-Me)2(dpm)] utilizes the overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound This suggests that the energy transfer efficiency is high. It was suggested that a light-emitting device with high external quantum efficiency could be obtained.

[0416] Here, the emission spectrum 27 is on the shorter wavelength (higher energy) side than the emission spectrum 26. The peak of the emission spectrum 27 is the same as the peak of the emission spectrum 26. As a result, in Figure 52, the absorption spectrum The emission spectrum that overlaps most with the absorption band that strongly contributes to the emission of the nucleon is Specifically, the peak of the absorption spectrum of the absorption band (52 The difference between the peak in the emission spectrum (shoulder peak around 0 nm) and the peak in the emission spectrum26 is 0.35 eV. The peak of the absorption spectrum of the absorption band (shoulder peak around 520 nm) and the emission spectrum The difference between the peaks of spectrum 27 was 0.01 eV.

[0417] The difference between the peaks of the emission spectrum 26 and the emission spectrum 27 is This is thought to be due to the difference in LUMO levels between DBTPDBq-II and DBTBIm-II. Specifically, the LUMO level of 2mDBTPDBq-II is -2.95 eV. In contrast, the LUMO level of DBTBIm-II was -2.52 eV (CV (Values ​​calculated by measurement). Compared to 2mDBTPDBq-II, DBTBIm-II is L Because the UMO level is high (shallow), even if it is mixed with 1'-TNATA, which has a high HOMO level, it is not mixed. The peak of the emission spectrum of the composite material was not too long wavelength (i.e., the emission spectrum 27 has a peak at a shorter wavelength side than the emission spectrum of 26).

[0418] From the above, the mixed material of DBTBIm-II and 1'-TNATA and [Ir(mp The light-emitting device using 2mDBTPDBq-II and 1'-T The light-emitting device using the mixed material of NATA and [Ir(mppr-Me)2(dpm)] Compared to the conventional method, there is a greater overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound. This suggests that the energy transfer efficiency is higher because the energy transfer is performed using the This suggests that a light-emitting device with higher external quantum efficiency can be obtained.

[0419] Furthermore, from this example, it was found that the first organic compound can be changed without changing the second organic compound. By simply using the compound, the emission spectrum of the mixed material of the first organic compound and the second organic compound and the phosphorescence It was found that the overlap of the absorption spectra of the compounds can be increased. When changing the emission color (position of the absorption band that strongly contributes to the emission of the absorption spectrum), However, by simply changing the first organic compound, it is possible to obtain a combination that increases the overlap. It was suggested that a light-emitting device with high external quantum efficiency and long life could be obtained. [Example]

[0420] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in the above are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0421] The method for fabricating the light-emitting elements 13 and 14 of this example will be described below.

[0422] (Light-emitting element 13) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0423] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0424] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0425] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about 1000 kJ / cm, BPAFLP and molybdenum oxide (VI ) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of PAFLP to molybdenum oxide was 4:2 (=BPAFLP:molybdenum oxide). The value was adjusted to be 0.

[0426] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0427] Furthermore, 2mDBTPDBq-II, 1'-TNATA and [Ir(mppr-Me)2 (dpm)] was co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. 2mDBTPDBq-II, 1'-TNATA and [Ir(mppr-Me)2(dpm )] weight ratio was 0.8:0.2:0.05 (=2mDBTPDBq-II:1'-TN ATA:[Ir(mppr-Me)2(dpm)]). The thickness of the layer 1113 was set to 20 nm.

[0428] Next, 2mDBTPDBq-II was formed on the light-emitting layer 1113 to a thickness of 30 nm. A first electron transport layer 1114a was formed.

[0429] Next, a film of BPhen was formed on the first electron transport layer 1114a to a thickness of 20 nm. Then, a second electron transport layer 1114b was formed.

[0430] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0431] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light emitting element 13 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0432] (Light emitting element 14) The light-emitting layer 1113 of the light-emitting element 14 is composed of DBTBIm-II, 1'-TNATA, and [Ir( The film was formed by co-evaporation of DBTBIm- The weight ratio of II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)] was 0. 8:0.2:0.05(=DBTBIm-II:1'-TNATA:[Ir(mppr- The thickness of the light-emitting layer 1113 was adjusted to 20 nm. It was decided.

[0433] The first electron transport layer 1114a of the light emitting element 14 is made of DBTBIm-II with a thickness of 30 nm. The layers other than the light-emitting layer 1113 and the first electron transport layer 1114a were formed as follows. was fabricated in the same manner as in the light-emitting device 13.

[0434] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0435] Table 15 shows the element structures of the thus obtained light-emitting elements 13 and 14.

[0436] [Table 15]

[0437] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0438] FIG. 53 shows the current density-luminance characteristics of the light-emitting elements 13 and 14. In FIG. The horizontal axis is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness The brightness characteristics are shown in Figure 54. In Figure 54, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and the luminance-current efficiency characteristics are shown in Figure 55. In Figure 55, the horizontal axis represents the luminance (c d / m 2 The vertical axis represents the current efficiency (cd / A), and the vertical axis represents the luminance vs. external quantum efficiency characteristics. 56. In FIG. 56, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the external quantum efficiency (% ) is shown.

[0439] Furthermore, the luminance of the light-emitting element 13 and the light-emitting element 14 is 860 cd / m 2 Voltage (V) , current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A), power The efficiency (lm / W) and external quantum efficiency (%) are shown in Table 16.

[0440] [Table 16]

[0441] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting elements 13 and 14 were In FIG. 57, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 16, 860 cd / m 2 The light emitting element 13 and the light emitting element The CIE chromaticity coordinates of the color 14 were (x,y) = (0.53,0.46). The light-emitting elements 13 and 14 are derived from [Ir(mppr-Me)2(dpm)]. It was found that orange light emission was obtained.

[0442] As can be seen from Table 16 and FIGS. 53 to 56, the light-emitting elements 13 and 14 exhibited a current The efficiency, power efficiency, and external quantum efficiency all showed high values.

[0443] The light-emitting devices 13 and 14 were the same as those in Example 15, except that the ... BTBIm-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)] , was used in the light-emitting layer. The emission spectrum of the mixture of I and 1'-TNATA (emission spectrum of the exciplex) is contributes strongly to the emission in the absorption spectrum of [Ir(mppr-Me)2(dpm)]. The overlap with the absorption band that is thought to be the source of the light is large. Since energy is transferred using In particular, the emission spectrum of the mixture of DBTBIm-II and 1'-TNATA The emission spectrum of the mixture of 2mDBTPDBq-II and 1'-TNATA was Therefore, the light emitting device 14 utilizes the large overlap. Since the energy transfer occurs through the light emitting element 13, the energy transfer efficiency is higher than that of the light emitting element 13. It is considered that the quantum efficiency is high. The energy value of the peak in the emission spectrum of the complex and the lowest energy side of the absorption spectrum It was found that the difference between the energy value of the absorption band peak and that of the do.

[0444] In this example, the first organic compound (corresponding to 1'-TNATA) was used without changing the second organic compound. Change the organic compound (use DBTBIm-II instead of 2mDBTPDBq-II) By simply using the ZnO-based GaN layer, a light-emitting device with even higher external quantum efficiency was obtained.

[0445] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that [Example]

[0446] In this example, a first organic compound, which can be applied to a light-emitting element of one embodiment of the present invention, An example of a combination of the second organic compound and the phosphorescent compound will be described with reference to FIG. do.

[0447] The phosphorescent compound used in this example is [Ir(mppr-Me)2(dpm)]. The first organic compound used in this example is 2mDBTPDBq-II. The second organic compounds used in the examples are PCBNBB and 9-phenyl-9H-3-(9- phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP) The chemical formulas of the materials used in this example are shown below. The academic ceremony is omitted.

[0448] [ka]

[0449] <Absorption spectrum> Figure 58(A)(B) shows the dimer of the phosphorescent compound [Ir(mppr-Me)2(dpm)]. The ultraviolet-visible absorption spectrum (hereinafter simply referred to as the absorption spectrum) of the chloromethane solution is shown below. The absorption spectrum was measured using a UV-visible spectrophotometer (V550 model, manufactured by JASCO Corporation). A dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were taken at room temperature. went.

[0450] <Emission spectrum> Also, Figure 58(A)(B) shows a thin film of the first organic compound, 2mDBTPDBq-II. Emission spectrum of the second organic compound, PCBNBB (Emission spectrum 28), The emission spectrum of the thin film of the second organic compound, PCCP (Emission Spectrum 29) Optical spectrum (emission spectrum 30), mixture of 2mDBTPDBq-II and PCBNBB The emission spectrum of the thin film of the material (Emission spectrum 31), and 2mDBTPDBq-II and The emission spectrum of a thin film of the PCCP mixture (Emission spectrum 32) is shown in Figure 58(A). ), the horizontal axis represents wavelength (nm) and the vertical axis represents molar absorption coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary units). In Figure 58(B), the horizontal axis represents energy (eV ), and the vertical axis represents the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary unit) vinegar.

[0451] From the absorption spectrum of Figure 58(A), [Ir(mppr-Me)2(dpm)] is It can be seen that there is a broad absorption band around 0 nm. This absorption band strongly contributes to the emission. It is thought that this is an absorption band.

[0452] Emission spectrum of the mixture of 2mDBTPDBq-II and PCBNBB (Emission spectrum 31), and the emission spectrum of the mixture of 2mDBTPDBq-II and PCCP (emission spectrum The spectra 32) are located at longer wavelengths (lower energy) than the emission spectra of the individual elements. This indicates that 2mDBTPDBq-II and PCBNB It was suggested that mixing B leads to the formation of an exciplex. It was suggested that exciplexes were formed by mixing q-II with PCCP.

[0453] The emission spectrum of the above mixed material has a peak of [Ir(mppr-Me)2(dpm)]. The absorption spectrum has a large overlap with the absorption band that is thought to strongly contribute to the emission. Therefore, the mixed material of 2mDBTPDBq-II and PCBNBB, and [Ir( mppr-Me)2(dpm)] and 2mDBTPDBq-II and PC The light-emitting device using the mixed material of CP and [Ir(mppr-Me)2(dpm)] By utilizing the overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound, This suggests that the energy transfer efficiency is high. It was suggested that a light-emitting device with high quantum efficiency could be obtained.

[0454] Furthermore, from this example, one of the first organic compound and the second organic compound that form an exciplex As the compound, not only aromatic amine compounds but also carbazole compounds can be used. It was suggested that this is the case. [Example]

[0455] In this example, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. The materials used in the above are the same as those used in the previous examples, and therefore the chemical formulas are omitted.

[0456] The method for fabricating the light-emitting elements 15 and 16 of this example will be described below.

[0457] (Light emitting element 15) First, a film of ITSO was formed on a glass substrate 1100 by sputtering, and the film served as an anode. The first electrode 1101 was formed to a thickness of 110 nm and an area of ​​2 mm x 2 mm.

[0458] Next, as a pretreatment for forming a light emitting element on the substrate 1100, the substrate surface is washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0459] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170° C. for 30 minutes in the heating chamber of the device, the substrate 1100 was It was left to cool for about 0 minutes.

[0460] Next, the surface on which the first electrode 1101 is formed is placed downward. The substrate 1100 thus formed is fixed to a substrate holder provided in a vacuum deposition apparatus, and 10 -4 P After the pressure was reduced to about 1000 kJ / cm, BPAFLP and molybdenum oxide (VI ) was co-evaporated to form a hole injection layer 1111. The thickness of the layer was set to 40 nm. The weight ratio of PAFLP to molybdenum oxide was 4:2 (=BPAFLP:molybdenum oxide). The value was adjusted to be 0.

[0461] Next, BPAFLP was formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0462] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2(d pm)] was co-evaporated to form the light-emitting layer 1113 on the hole transport layer 1112. DBTPDBq-II, PCBNBB and [Ir(mppr-Me)2(dpm)] The ratio was 0.8:0.2:0.05 (=2mDBTPDBq-II:PCBNBB:[I r(mppr-Me)2(dpm)]). The film thickness was set to 20 nm.

[0463] Next, 2mDBTPDBq-II, PCBNBB, and [Ir(mpp r-Me)2(dpm)] was co-evaporated to form a first electron transport layer 1114a on the light-emitting layer 1113. Here, 2mDBTPDBq-II, PCBNBB and [Ir(mppr- The weight ratio of 2mDBTPDBq- II: PCBNBB: [Ir(mppr-Me)2(dpm)] The thickness of the first electron transport layer 1114a was set to 40 nm.

[0464] Next, BPhen was deposited on the first electron transport layer 1114a to a thickness of 10 nm. Then, a second electron transport layer 1114b was formed.

[0465] Furthermore, LiF was evaporated onto the second electron transport layer 1114b to a thickness of 1 nm to form an electron injection layer. 1115 was formed.

[0466] Finally, a 200 nm film of aluminum was deposited as the second electrode 1103, which served as the cathode. The light emitting element 15 of this example was fabricated by vapor deposition so as to have a thickness of 1000 nm.

[0467] (Light emitting element 16) The light-emitting layer 1113 of the light-emitting element 16 contains 2mDBTPDBq-II, PCCP, and [Ir(m ppr-Me)2(dpm)]. The weight ratio of q-II, PCCP, and [Ir(mppr-Me)2(dpm)] was 0.8: 0.2:0.05(=2mDBTPDBq-II:PCCP:[Ir(mppr-Me) 2 (dpm)]). The thickness of the light-emitting layer 1113 was set to 20 nm. The light-emitting element was fabricated in the same manner as in the light-emitting element 15, except for the light-emitting layer 1113.

[0468] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0469] Table 17 shows the element structures of the thus obtained light-emitting elements 15 and 16.

[0470] [Table 17]

[0471] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0472] FIG. 59 shows the current density-luminance characteristics of the light-emitting elements 15 and 16. In FIG. The horizontal axis is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness The brightness characteristics are shown in Figure 60. In Figure 60, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and the luminance-current efficiency characteristics are shown in Figure 61. In Figure 61, the horizontal axis represents the luminance (c d / m 2 The vertical axis represents the current efficiency (cd / A), and the vertical axis represents the luminance vs. external quantum efficiency characteristics. 62. In FIG. 62, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the external quantum efficiency (% ) is shown.

[0473] Furthermore, the luminance of the light-emitting element 15 and the light-emitting element 16 is 1200 cd / m 2 Voltage at (V ), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A), power The power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 18.

[0474] [Table 18]

[0475] Furthermore, the emission spectra when a current of 0.1 mA is applied to the light-emitting elements 15 and 16 are shown in Table 1. , as shown in Figure 63. In Figure 63, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 18, 1200 cd / m 2 CIE 15 luminance at luminance of The chromaticity coordinates are (x,y)=(0.54,0.45), which is 1200cd / m 2 When the brightness is The CIE chromaticity coordinates of the light-emitting element 16 were (x, y) = (0.54, 0.46). From the results, it can be seen that the light-emitting elements 15 and 16 have the same structure as [Ir(mppr-Me)2(dpm)] It was found that orange luminescence due to

[0476] As can be seen from Table 18 and FIGS. 59 to 62, the light-emitting elements 15 and 16 exhibited a current The efficiency, power efficiency, and external quantum efficiency all showed high values.

[0477] Light-emitting devices 15 and 16 were prepared by combining 2mDBTPDBq-II shown in Example 17 and P CBNBB or PCCP and [Ir(mppr-Me)2(dpm)] are used for the light-emitting layer. From Example 17, it was found that 2mDBTPDBq-II was mixed with PCBNBB or PCCP. The emission spectrum of the composite material (emission spectrum of the exciplex) is [Ir(mppr-Me)2 (dpm)] absorption spectrum, overlapping with the absorption band that is thought to strongly contribute to the emission. The light emitting element 15 and the light emitting element 16 transfer energy by utilizing this overlap. Therefore, it is thought that the energy transfer efficiency is high and the external quantum efficiency is high.

[0478] In addition, this example shows that not only aromatic amine compounds (PCBNBB) but also carbazole Even when using a fluorine-containing compound (PCCP), it is possible to form an exciplex and achieve high external quantum efficiency. It was found that a light-emitting element with high

[0479] From the above results, it can be seen that by applying one embodiment of the present invention, a device with high external quantum efficiency can be realized. It was shown that

[0480] (Reference example 1) The organometallic complex used in the above examples, (acetylacetonato)bis(4,6-diphenylpiperidinyl) Bis[2-(6-phenyl-4-pyrimidinato)iridium(III)] [2,4-pentanedionato-κ](2,4-diol-κN3)phenyl-κC](2,4-pentanedionato-κ 2 O,O') Iridium (III)) (abbreviation: [Ir(dppm)2(acac)]) is shown below. The structure of [Ir(dppm)2(acac)] is shown below.

[0481] [ka]

[0482] <Step 1: Synthesis of 4,6-diphenylpyrimidine (abbreviation: Hdppm)> First, 5.02 g of 4,6-dichloropyrimidine, 8.29 g of phenylboronic acid, and sodium carbonate were added. 7.19g of sodium, bis(triphenylphosphine)palladium(II) dichloride (abbreviated Name: Pd(PPh3)2Cl2) 0.29 g, water 20 mL, acetonitrile 20 mL, The reaction vessel was placed in a recovery flask equipped with a reflux condenser, and the inside of the flask was replaced with argon. The sample was heated by irradiating it with microwaves (2.45 GHz, 100 W) for 60 minutes. 2.08g of boronic acid, 1.79g of sodium carbonate, 0.07g of Pd(PPh3)2Cl2 0g, 5mL of water, and 5mL of acetonitrile were placed in a flask and microwaved again (2.45G The solution was heated by irradiating it with a 100W (100Hz) lamp for 60 minutes. The organic layer was extracted with chloromethane. The resulting extract was washed with water and then extracted with magnesium sulfate. The dried solution was filtered. The solvent of this solution was evaporated, and the resulting residue was The product was purified by silica gel column chromatography using dichloromethane as a developing solvent. The rimidine derivative Hdppm was obtained (yellowish white powder, 38% yield). A microwave synthesizer (Discover manufactured by CEM) was used for this synthesis. The synthesis scheme (a-1) is shown below.

[0483] [ka]

[0484] Step 2: Di-μ-chloro-bis[bis(4,6-diphenylpyrimidinato)iridi Synthesis of [Ir(dppm)2Cl]2 Next, 15 mL of 2-ethoxyethanol, 5 mL of water, and the Hdppm1 obtained in Step 1 above were added. 0.10g, iridium chloride hydrate (IrCl3·H2O) 0.69g, The flask was then filled with argon. The mixture was irradiated with a 5 GHz 100 W power source for 1 hour to cause a reaction. After the solvent was distilled off, the resulting residue was After filtration and washing with ethanol, the dinuclear complex [Ir(dppm)2Cl]2 (red Brown powder, 88% yield. The synthesis scheme for step 2 (a-2) is shown below.

[0485] [ka]

[0486] Step 3: (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridide Synthesis of Ir(III) (abbreviation: [Ir(dppm)2(acac)]) Furthermore, 40 mL of 2-ethoxyethanol and [Ir(dppm)2 obtained in Step 2 above] 1.44 g of Cl2, 0.30 g of acetylacetone, and 1.07 g of sodium carbonate were refluxed. The flask was then filled with argon. The reaction was carried out by irradiating the mixture with microwaves (2.45 GHz, 120 W) for 60 minutes. The resulting residue was dissolved in dichloromethane and filtered to remove insoluble matter. The solution was washed with saturated saline and dried over magnesium sulfate. After distilling off the solvent from this solution, the resulting residue was diluted with dichloromethane:ethyl acetate=50: The product was purified by silica gel column chromatography using 1 (volume ratio) as the developing solvent. The target orange powder was obtained by recrystallization in a mixed solvent of dichloromethane and hexane. The compound was obtained (yield 32%). The synthesis scheme (a-3) of step 3 is shown below.

[0487] [ka]

[0488] Nuclear magnetic resonance spectroscopy ( 1 H NMR analysis results The results are shown below. From these results, it was found that the organometallic complex [Ir(dppm)2(acac)] was obtained. It was found that

[0489] 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),7.55-7.6 3(m,6H),7.77(d,2H),8.17(s,2H),8.24(d,4H) ,9.17(s,2H).

[0490] (Reference example 2) The organometallic complex used in the above examples, (acetylacetonato)bis(6-methyl-4-phenyl) Bis[2-(6-methyl-4-pyrimidinato)iridium(III)] 2,4-Pentanedionato-κN3)phenyl-κC](2,4-pent ... 2 O,O') Iriji A specific example of the synthesis of Ir(mppm)2(acac) is shown below. The structure of [Ir(mppm)2(acac)] is shown below.

[0491] [ka]

[0492] <Step 1: Synthesis of 4-methyl-6-phenylpyrimidine (abbreviation: Hmppm)> First, 4.90 g of 4-chloro-6-methylpyrimidine, 4.80 g of phenylboronic acid, and charcoal sodium phosphate 4.03g, bis(triphenylphosphine)palladium(II) dichloride 0.16 g of Pd(PPh3)2Cl2, 20 mL of water, 10 mL of acetonitrile L was placed in a recovery flask equipped with a reflux condenser, and the inside of the flask was replaced with argon. The material was heated by irradiating it with microwaves (2.45 GHz, 100 W) for 60 minutes. 2.28 g of phenylboronic acid, 2.02 g of sodium carbonate, Pd(PPh3)2Cl2 0.082g, 5mL of water, and 10mL of acetonitrile were placed in a flask and microwaved again ( The solution was heated by irradiating it with a 2.45 GHz (100 W) power for 60 minutes. The extract was diluted with saturated aqueous sodium carbonate, water, The solution was then washed with saturated saline and dried over magnesium sulfate. The solvent was removed from this solution by distillation, and the resulting residue was diluted with dichloromethane:ethyl acetate=9 The desired product was purified by silica gel column chromatography using a 1:1 (volume ratio) developing solvent. The pyrimidine derivative Hmppm was obtained (orange oil, 46% yield). The irradiation was carried out using a microwave synthesis device (Discover manufactured by CEM). The synthesis scheme (b-1) is shown below.

[0493] [ka]

[0494] Step 2: Di-μ-chloro-bis[bis(6-methyl-4-phenylpyrimidinato) Synthesis of [Iridium(III)] (abbreviation: [Ir(mppm)2Cl]2) Next, 15 mL of 2-ethoxyethanol, 5 mL of water, and Hmppm1 obtained in Step 1 above were added. 0.51g, 1.26g of iridium chloride hydrate (IrCl3·H2O) The flask was then filled with argon. The mixture was irradiated with a 5 GHz 100 W power source for 1 hour to cause a reaction. After the solvent was distilled off, the resulting residue was The binuclear complex [Ir(mppm)2Cl]2 was obtained by washing with ethanol and filtering. (Dark green powder, 77% yield). The synthesis scheme (b-2) of Step 2 is shown below.

[0495] [ka]

[0496] Step 3: (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato) Synthesis of Iridium(III) (abbreviation: [Ir(mppm)2(acac)]) Furthermore, 40 mL of 2-ethoxyethanol and the binuclear complex [Ir(mp pm)2Cl]2 1.84 g, acetylacetone 0.48 g, sodium carbonate 1.73 g The contents were placed in a recovery flask equipped with a reflux condenser, and the atmosphere in the recovery flask was replaced with argon. The reaction was carried out by irradiating with microwaves (2.45 GHz, 120 W) for 60 minutes. The resulting residue was dissolved in dichloromethane and filtered to remove insoluble matter. The solution was washed with water, then saturated saline, and dried over magnesium sulfate. The solution was filtered, and the solvent was evaporated, and the resulting residue was diluted with dichloromethane:ethyl acetate The product was purified by silica gel column chromatography using a 4:1 (volume ratio) developing solvent. After that, the target substance was recrystallized in a mixed solvent of dichloromethane and hexane to obtain a yellow crystalline solid. It was obtained as a powder (yield 22%). The synthesis scheme of step 3 (b-3) is shown below.

[0497] [ka]

[0498] Nuclear magnetic resonance spectroscopy ( 1 H NMR analysis results The results are shown below. From these results, it was found that the organometallic complex [Ir(mppm)2(acac)] was obtained. It was found that

[0499] 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,2 H),7.61-7.63(m,4H),8.97(s,2H).

[0500] (Reference example 3) The organometallic complex used in the above examples, (acetylacetonato)bis(6-tert-butyl -4-phenylpyrimidinato)iridium(III) (synonym: bis[2-(6-tert -butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato- κ 2 O,O')iridium(III) (abbreviation: [Ir(tBuppm)2(acac) The structure of [Ir(tBuppm)2(acac)] is shown below. vinegar.

[0501] [ka]

[0502] Step 1: 4-tert-butyl-6-phenylpyrimidine (abbreviation: HtBuppm ) Synthesis First, 22.5 g of 4,4-dimethyl-1-phenylpentane-1,3-dione and formaldehyde 50 g of mide was placed in a recovery flask equipped with a reflux condenser, and the inside of the flask was replaced with nitrogen. The reaction solution was refluxed for 5 hours by heating. The organic layer was extracted with dichloromethane, and the obtained organic layer was washed with water and saturated brine. The solution was washed and dried over magnesium sulfate. After drying, the solution was filtered. After distilling off the solvent, the resulting residue was mixed with hexane:ethyl acetate=10:1 (volume ratio) as a developing solvent. The pyrimidine derivative HtBupp was purified by silica gel column chromatography using a solvent. m was obtained (colorless oil, 14% yield). The synthesis scheme of step 1 is shown in (c-1) below. vinegar.

[0503] [ka]

[0504] Step 2: Di-μ-chloro-bis[bis(6-tert-butyl-4-phenylpyridine] Synthesis of [Ir(tBuppm)2Cl]2 > Next, 15 mL of 2-ethoxyethanol, 5 mL of water, and the HtBupp obtained in step 1 above were added. 1.49 g of iridium chloride hydrate (IrCl3·H2O) was added to a The flask was then purged with argon. The mixture was irradiated with a 5 GHz 100 W power source for 1 hour to cause a reaction. After the solvent was distilled off, the resulting residue was After suction filtration and washing with ethanol, the binuclear complex [Ir(tBuppm)2Cl]2 (yellow) was obtained. Green powder, 73% yield. The synthesis scheme for step 2 is shown below in (c-2).

[0505] [ka]

[0506] Step 3: (acetylacetonato)bis(6-tert-butyl-4-phenylpyridine) Iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]) > Furthermore, 40 mL of 2-ethoxyethanol and the binuclear complex [Ir(tB uppm)2Cl]21.61 g, acetylacetone 0.36 g, sodium carbonate 1. 27 g was placed in a recovery flask equipped with a reflux condenser, and the atmosphere in the flask was replaced with argon. The mixture was irradiated with microwaves (2.45 GHz, 120 W) for 60 minutes to react. The resulting residue was filtered off with ethanol and washed with water and ethanol. Dissolved in chloromethane, Celite (Wako Pure Chemical Industries, Ltd., Catalog No. 531-1 The mixture was filtered through a filter aid consisting of layers of 6855, alumina, and celite in that order. The solid obtained by removal of the solvent was recrystallized in a mixed solvent of dichloromethane and hexane, The target product was obtained as a yellow powder (yield 68%). The synthesis scheme of step 3 is shown below (c-3 ) shown.

[0507] [ka]

[0508] Nuclear magnetic resonance spectroscopy ( 1 H NMR analysis results The results are shown below. From these results, it is clear that the organometallic complex [Ir(tBuppm)2(acac)] It was found that it was obtained.

[0509] 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).

[0510] (Reference example 4) The 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[ f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) synthesis method is explained. .

[0511] [ka]

[0512] 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxa Synthesis of phosphorus (abbreviation: 2mDBTPDBq-II)≫ 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxalate The synthesis scheme of the compound (abbreviation: 2mDBTPDBq-II) is shown in (d-1).

[0513] [ka]

[0514] In a 2 L three-neck flask, add 5.3 g (20 mmol) of 2-chlorodibenzo[f,h]quinoxaline. ), 3-(dibenzothiophen-4-yl)phenylboronic acid 6.1g (20mmol) , tetrakis(triphenylphosphine)palladium(0) 460 mg (0.4 mmol ), 300 mL of toluene, 20 mL of ethanol, and 20 mL of 2 M potassium carbonate aqueous solution were added. This mixture was degassed by stirring under reduced pressure, and the atmosphere inside the three-neck flask was replaced with nitrogen. The mixture was stirred at 100°C for 7.5 hours under a nitrogen atmosphere. The mixture was filtered to obtain a white residue. The residue was washed with water and then with ethanol. The resulting solid was dissolved in approximately 600 mL of hot toluene and then passed through a pad of Celite and Floridian. The resulting filtrate was concentrated to about 700 mL. The product was purified by silica gel column chromatography using hot toluene. The solid obtained here was mixed with acetone and ethanol and then subjected to ultrasonic irradiation. After irradiation, the resulting suspension was filtered and dried to give a white powder (yield: 7.85 g, The yield was 80%.

[0515] The above target material was relatively soluble in hot toluene, but was prone to precipitation when cooled. In addition, it was poorly soluble in other organic solvents such as acetone and ethanol. By taking advantage of the difference in decomposition rate, it was possible to synthesize the compound in a simple and efficient manner. After the reaction is complete, the mixture is returned to room temperature and the precipitated solid is collected by filtration, which allows most of the impurities to be easily removed. In addition, column chromatography using hot toluene as a developing solvent was performed. This enabled us to easily purify target compounds that tend to precipitate.

[0516] 4.0 g of the obtained white powder was purified by train sublimation. The white powder was heated to 300°C under the conditions of a pressure of 5.0 Pa and an argon flow rate of 5 mL / min. After purification by sublimation, 3.5 g of the target white powder was obtained in a yield of 88%.

[0517] Nuclear magnetic resonance spectroscopy ( 1 1 H NMR) confirmed that this compound was the target 2-[3-(di- benzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2m It was confirmed that the product was DBTPDBq-II.

[0518] of the obtained material 1 The 1 H NMR data is shown below. 1 H NMR(CDCl3,300MHz):δ(ppm)=7.45-7.52(m ,2H), 7.59-7.65(m,2H), 7.71-7.91(m,7H), 8.2 0-8.25(m,2H), 8.41(d,J=7.8Hz,1H), 8.65(d,J =7.5Hz,2H), 8.77-8.78(m,1H), 9.23(dd,J=7.2 Hz,1.5Hz,1H), 9.42(dd,J=7.8Hz,1.5Hz,1H), 9 .48(s,1H). [Explanation of symbols]

[0519] 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 Electronic Relay Layer 708 Composite material layer 800 First EL layer 801 Second EL layer 803 Charge generation layer 1100 board 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. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.2 eV; Light-emitting element.

2. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.1 eV; Light-emitting element.

3. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.2 eV; Light-emitting element.

4. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.1 eV; Light-emitting element.

5. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.2 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Chemistry 1】 Light-emitting element.

6. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.1 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Chemistry 2】 Light-emitting element.

7. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.2 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Transformation 3】 Light-emitting element.

8. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a phosphorescent compound; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band in the absorption spectrum of the phosphorescent compound is within 0.1 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Chemistry 4】 Light-emitting element.

9. In any one of claims 1 to 8, T of the first organic compound １ The level is the T １ Higher than the level, T of the second organic compound １ The level is the T １ A light-emitting element that is higher than the level.

10. In any one of claims 1 to 9, The light-emitting device comprises the phosphorescent compound, the absorption band of which has a peak at the longest wavelength in the wavelength range of 490 nm or more and 530 nm or less.

11. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.2 eV; Light-emitting element.

12. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.1 eV; Light-emitting element.

13. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.2 eV; Light-emitting element.

14. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.1 eV; Light-emitting element.

15. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.2 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Transformation 5】 Light-emitting element.

16. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound substituted at the 3-position of the carbazole ring, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.1 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Transformation 6】 Light-emitting element.

17. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.2 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Transformation 7】 Light-emitting element.

18. A light-emitting element having a pair of electrodes, A light-emitting layer is provided between the pair of electrodes, the light-emitting layer includes a first organic compound, a second organic compound, and a light-emitting material; the luminescent material comprises iridium; the first organic compound and the second organic compound are a combination that forms an exciplex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound in which two carbazole rings are bonded to each other at the 3-position, a difference between the peak energy of the emission spectrum of the exciplex and the peak energy of the lowest-energy absorption band of the absorption spectrum of the luminescent substance is within 0.1 eV; (However, this does not include the case where the light-emitting layer contains the following compound (1-1) or compound 3.) 【Transformation 8】 Light-emitting element.

19. In any one of claims 11 to 18, T of the first organic compound １ The level is the T １ Higher than the level, T of the second organic compound １ The level is the T １ A light-emitting element that is higher than the level.

20. In any one of claims 11 to 19, A light-emitting device, wherein the peak of the absorption band on the longest wavelength side of the light-emitting substance is in the wavelength range of 490 nm or more and 530 nm or less.

21. In any one of claims 1 to 20, The light-emitting element, wherein the second organic compound is a carbazole compound that is not an aromatic amine compound.

22. In any one of claims 1 to 21, a hole injection layer between the pair of electrodes, The light-emitting device, wherein the hole injection layer includes an electron acceptor.

23. In any one of claims 1 to 21, a hole injection layer between the pair of electrodes, The light-emitting device, wherein the hole injection layer contains a first aromatic amine compound.

24. In any one of claims 1 to 21, a hole injection layer between the pair of electrodes, The light-emitting device, wherein the hole injection layer includes an electron acceptor and a first aromatic amine compound.

25. In claim 23 or claim 24, The light-emitting device, wherein the first aromatic amine compound is an aromatic amine compound having a fluorenyl group.

26. In any one of claims 1 to 25, a hole transport layer between the pair of electrodes and in contact with the light-emitting layer; The light-emitting device, wherein the hole transport layer contains a second aromatic amine compound.

27. In claim 26, The light-emitting device, wherein the second aromatic amine compound is an aromatic amine compound having a fluorenyl group.

28. In claim 26 or claim 27, The second aromatic amine compound is an aromatic amine compound having a 9-phenylfluoren-9-yl group.

29. In any one of claims 1 to 28, an electron transport layer between the pair of electrodes and in contact with the light-emitting layer; The light-emitting device, wherein the electron transport layer comprises a second heteroaromatic compound.

30. In any one of claims 1 to 28, The light-emitting element has a first electron transport layer and a second electron transport layer between the pair of electrodes.

31. A light-emitting device comprising the light-emitting element according to claim 1 .

32. A lighting device comprising the light-emitting device according to claim 31.

33. An electronic device comprising the light-emitting device according to claim 31.

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