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

Abstract

To provide a light-emitting element having high external quantum efficiency. A light-emitting element with low driving voltage is provided.SOLUTION: A light-emitting element 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, an emission spectrum of the exciplex overlaps with an absorption band located on the longest wavelength side in an absorption spectrum of the phosphorescent compound, and a peak wavelength of the emission spectrum of the exciplex is longer than or equal to a peak wavelength of the absorption band located on the longest wavelength side in the absorption spectrum of the phosphorescent compound.SELECTED DRAWING: Figure 1

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. Characteristics include being able to reduce the size of the mold, responding quickly to input signals, and being able to be driven at low DC voltage. 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] As mentioned above, organic EL elements are being considered for use in displays and lighting. One of the issues to be addressed is reducing power consumption. Therefore, it is important to reduce the driving voltage of the organic EL element.

[0010] 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 low driving voltage. .

[0011] The invention disclosed below aims to solve at least one of the above problems. Let's say. [Means for solving the problem]

[0012] 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 emission spectrum of the exciplex is the closest to the absorption spectrum of the phosphorescent compound. The peak wavelength of the emission spectrum of the exciplex overlaps with the absorption band located on the long wavelength side, and the peak wavelength of the emission spectrum of the exciplex becomes the peak wavelength of the phosphorescence. The emission wavelength is equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side of the absorption spectrum of the compound. It is an 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 a first organic compound and a second organic compound. The emission spectrum of the exciplex is the absorption spectrum of the phosphorescent compound. The absorption band of the exciplex overlaps with the longest wavelength of the exciplex, and the peak wavelength of the exciplex emission spectrum is The difference between the peak wavelength of the emission spectrum of the phosphorescent compound and the peak wavelength of the emission spectrum of the phosphorescent compound is 30 nm or less. do.

[0014] 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 emission spectrum of the exciplex is the absorption spectrum of the phosphorescent compound. The peak wavelength of the emission spectrum of the exciplex overlaps with the absorption band located at the longest wavelength side of the molecule. , the peak wavelength of the absorption band located on the longest wavelength side of the absorption spectrum of the phosphorescent compound or more, The light-emitting element has a wavelength equal to or less than the peak wavelength of the emission spectrum of the photoactive compound. The difference between the peak wavelength of the emission spectrum of the phosphorescent compound and the peak wavelength of the emission spectrum of the phosphorescent compound is It is preferably 30 nm or less.

[0015] In another embodiment of the present invention, an exciplex is formed from a singlet exciton of a first organic compound. The light-emitting element is as described above.

[0016] Another aspect of the present invention is a method for producing a compound comprising: a first organic compound having an anion; a second organic compound having a cation; In the light-emitting element, an exciplex is formed from the above.

[0017] In the light-emitting element, the excitation energy of the exciplex is transferred to the phosphorescent compound, Preferably, the compound is phosphorescent.

[0018] 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.

[0019] In the above light-emitting element, the phosphorescent compound is preferably an organometallic complex.

[0020] 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]

[0021] 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 low driving voltage can be provided. [Brief explanation of the drawings]

[0022] [Figure 1] 3A and 3B are diagrams showing absorption spectra and emission spectra according to Example 1. FIG. [Figure 2] 3A and 3B are diagrams showing absorption spectra and emission spectra according to Example 1. FIG. [Figure 3] 3A and 3B are diagrams showing absorption spectra and emission spectra according to Example 1. FIG. [Figure 4] 3A and 3B are diagrams showing absorption spectra and emission spectra according to Example 1. FIG. [Figure 5] 1A and 1B illustrate a concept of one embodiment of the present invention. [Figure 6]FIG. 1 illustrates energy levels of an exciplex used in one embodiment of the present invention. [Figure 7] 1A and 1B illustrate light-emitting elements of one embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing the structure of a light-emitting element according to a second embodiment. [Figure 9] FIG. 10 is a graph showing voltage-luminance characteristics of the light-emitting element of Example 2. [Figure 10] FIG. 10 is a graph showing voltage-current characteristics of the light-emitting element of Example 2. [Figure 11] FIG. 10 is a graph showing luminance-power efficiency characteristics of the light-emitting element of Example 2. [Figure 12] FIG. 10 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 2. [Figure 13] FIG. 10 shows an emission spectrum of the light-emitting element of Example 2. [Figure 14] 10 shows the results of a reliability test of the light-emitting element of Example 2. FIG. [Figure 15] FIG. 10 is a diagram showing the relationship between the peak wavelength of the emission spectrum of the exciplex according to Example 3 and the HOMO level of the substance X. [Figure 16] FIG. 10 is a graph showing the relationship between the peak wavelength of the emission spectrum of the exciplex according to Example 3 and the external quantum efficiency of the light-emitting element. [Figure 17] FIG. 10 shows calculation results according to one embodiment of the present invention. [Figure 18] FIG. 10 shows calculation results according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] (Embodiment 1) In this embodiment, a light-emitting element of one embodiment of the present invention will be described.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] <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.

[0029] (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.

[0030] 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.

[0031] (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.

[0032] 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:

[0033] 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.

[0034] <Energy transfer process> The energy transfer process between molecules is described in detail below.

[0035] 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.

[0036] <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).

[0037]

number

[0038] 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.

[0039] 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).

[0040]

number

[0041] 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.

[0042] 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.

[0043]

number

[0044] First, from equation (3), the energy transfer efficiency Φ ETTo 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.

[0045] 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.

[0046] 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.

[0047] For example, in organometallic complexes, especially luminescent iridium complexes, the longest wavelength absorption band is In many cases, a broad absorption band appears around 500 to 600 nm (of course, this depends on the emission wavelength). (It may appear on the shorter or longer wavelength side depending on the wavelength.) This absorption band is mainly Triplet MLCT (Metal to Ligand Charge Transfer) However, this absorption band includes the triplet π-π * transitions and singlet MLCT transitions These overlap, resulting in a broad absorption spectrum at the longest wavelength side. In other words, the lowest singlet excited state and the lowest triplet excited state form an absorption band. The difference in state is small, and the absorption due to these states overlaps, resulting in the absorption spectrum at the longest wavelength side. It is thought that a broad absorption band is formed. Therefore, it is considered that the guest material is an organometallic complex. When using complexes (especially iridium complexes), the broad spectrum at the longest wavelength is It is preferable that the absorption band of the host material largely overlaps with the emission spectrum of the host material.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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 the inventors have achieved an external quantum efficiency of 27% or more (see FIG. 12, Example 2). This value is equal to or greater than the conventional theoretical limit of external quantum efficiency. In either case, an external quantum efficiency of 27% or more corresponds to an internal quantum efficiency of 100%. This is a useful method for achieving this. 20% is estimated to correspond to an internal quantum efficiency of 75% or less.

[0055] In this manner, by applying one embodiment of the present invention, a light-emitting element with high external quantum efficiency can be realized. It is possible.

[0056] <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 emission spectrum of the exciplex is the closest to the absorption spectrum of the phosphorescent compound. The peak wavelength of the emission spectrum of the exciplex overlaps with the absorption band on the long wavelength side, and the peak wavelength of the emission spectrum of the phosphorescent compound The light emitting element has a wavelength equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side of the absorption spectrum of the light emitting element. do.

[0057] The first organic compound and the second organic compound are reacted with each other through recombination (or recombination) of carriers (electrons and holes). The excited complex (also called exciplex) is formed by the singlet exciton. When the exciplex emits light, the emission wavelength is determined by the ratio of the first organic compound to the second organic compound. They exist at longer wavelengths than the respective emission wavelengths (fluorescence wavelengths). In other words, exciplexes By forming a fluorescent spectrum of the first organic compound and a fluorescent spectrum of the second organic compound, The tor can be converted to an emission spectrum located at longer wavelengths.

[0058] Therefore, as shown in FIG. 5, 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 can produce long wavelength emission. The spectrum can be obtained, and the overlap with the absorption band can be increased. The light-emitting element is formed by overlapping the emission spectrum of the exciplex with the absorption spectrum of the phosphorescent compound. Therefore, the energy transfer efficiency is high. In one embodiment, a light-emitting element with high external quantum efficiency can be realized.

[0059] 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.

[0060] 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.

[0061] 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).

[0062] 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.

[0063] The quantum chemistry calculation program used was Gaussian 09. The analysis was carried out using a high-performance computer (SGI, Altix4700).

[0064] First, the HOMO levels and The HOMO and LUMO levels were calculated. The distribution of MO is shown in FIG.

[0065] Figure 18(A1) shows the LUMO distribution of DBq alone, and Figure 18(A2) shows the LUMO distribution of DBq alone. 18(B1) shows the HOMO distribution of TPA alone, and Fig. 18(B2) shows the LUMO distribution of TPA alone. 8(B2) shows the distribution of the HOMO of TPA alone, and Fig. 18(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 18(C2). The distribution of O is shown.

[0066] As shown in Figure 17, 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 in Figure 18, the dimer of DBq and TPA The LUMO is located on the DBq side, and the HOMO is located on the TPA side.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In addition, in the light-emitting element of one embodiment of the present invention, the recombination of carriers (or singlet excitons) The threshold voltage at which an exciplex is formed is determined by the energy of the peak in the emission spectrum of the exciplex. For example, if the peak of the emission spectrum of an exciplex is at 620 nm (2 If the voltage is 0.0 eV, then the threshold voltage required to form the exciplex with electrical energy is The value is also around 2.0V.

[0076] Here, the energy of the peak in the emission spectrum of the exciplex is too high (the wavelength is too short). In this case, the voltage threshold at which the exciplex is formed also increases. A larger voltage is required to transfer energy to the phosphorescent compound and make the compound emit light. This is undesirable because it results in excessive energy consumption.

[0077] From this viewpoint, the lower the peak energy of the emission spectrum of the exciplex (the longer the wavelength), the more In other words, the light-emitting element of one embodiment of the present invention has the following characteristics: The peak wavelength of the emission spectrum of the exciplex is the longest wavelength in the absorption spectrum of the phosphorescent compound. Since the wavelength is equal to or greater than the peak wavelength of the absorption band located on the side of the Moreover, the light-emitting element of one embodiment of the present invention can emit light having a peak wavelength of 1000 nm in the emission spectrum of the exciplex. Even if the wavelength is equal to or greater than the peak wavelength of the absorption spectrum of the phosphorescent compound, the emission spectrum of the exciplex The absorption spectrum of phosphorescent compounds overlaps with that of the longest wavelength band. Since energy transfer is possible, high luminous efficiency can be obtained. High power consumption is achieved by reducing the driving voltage and achieving high luminous efficiency (external quantum efficiency). Efficiency can be achieved.

[0078] In the light-emitting device, the peak wavelength of the emission spectrum of the exciplex is particularly long, A light-emitting element with a low driving voltage can be obtained. This can be explained as follows.

[0079] In one embodiment of the present invention, the peak wavelength of the emission spectrum of the exciplex is equal to or smaller than the absorption spectrum of the phosphorescent compound. The wavelengths longer than the peak wavelength of the absorption band located on the longest wavelength side of the spectrum (i.e., the emission of the exciplex) The energy of the absorption peak of the phosphorescent compound is equal to or less than the energy of the absorption peak of the phosphorescent compound. Therefore, the light-emitting device is a device in which a phosphorescent compound emits light by recombination of carriers. The voltage at which exciplexes are formed by carrier recombination is lower than the voltage at which light begins to be emitted. is smaller.

[0080] That is, even if the voltage applied to the light-emitting element is less than the value at which the phosphorescent compound starts to emit light, When the carriers recombine to form an exciplex, a recombination current begins to flow in the light-emitting element. Therefore, a light emitting device with a lower driving voltage (good voltage-current characteristics) can be realized. do.

[0081] In addition, by the time the voltage reaches a value at which the phosphorescent compound starts to emit light, sufficient voltage is present in the light-emitting layer. There are sufficient carriers present, and the recombination of carriers that can contribute to the emission of phosphorescent compounds is smooth. Therefore, near the threshold voltage (light emission starting voltage) of the phosphorescent compound, In other words, the voltage-brightness characteristic rises at a voltage near the light emission start voltage. Since the change in the brightness can be made steeper, the driving voltage required for a desired brightness can be reduced. In addition, to obtain practical brightness, the phosphorescent compound must have a threshold voltage (light emission start voltage) or higher. Since the device is driven at a voltage of 1000 V, the light emitted by the phosphorescent compound is dominant, and the light-emitting device has high current efficiency. It can also be realized.

[0082] Note that the phosphorescent compound used in one embodiment of the present invention has a singlet absorption spectrum and a triplet absorption spectrum. In addition, the exciplex formed in one embodiment of the present invention has a singlet state. The peak of the emission spectrum from the triplet state is close to the peak of the emission spectrum from the triplet state. Therefore, the emission spectrum of the exciplex (usually from the singlet state) The peak of the emission spectrum from the phosphorescent compound is close to the peak of the emission spectrum from the phosphorescent compound. If present, triplet-state exciplexes quench the triplet excitation energy of phosphorescent compounds. In addition, exciplexes do not have absorption spectra in the first place. Therefore, the triplet excitation energy of the phosphorescent compound is transferred to the exciplex, resulting in quenching. This phenomenon itself is unlikely to occur. This shows a high efficiency, which is another advantage of using exciplexes.

[0083] 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 emission spectrum of the exciplex is the absorption spectrum of the phosphorescent compound. The absorption band of the exciplex overlaps with the longest wavelength of the exciplex, and the peak wavelength of the exciplex emission spectrum is The difference between the peak wavelength of the emission spectrum of the phosphorescent compound and the peak wavelength of the emission spectrum of the phosphorescent compound is 30 nm or less. do.

[0084] As mentioned above, the emission spectrum of an exciplex (usually the emission spectrum from the singlet state) The peak is located close to the peak of the emission spectrum of the phosphorescent compound, so that the driving voltage The effect of reducing the voltage is that the emission of the exciplex is enhanced. The region where the peak of the optical spectrum is within +30 nm of the peak of the emission spectrum of the phosphorescent compound The peak of the emission spectrum of the exciplex is clearly seen in the emission spectrum of the phosphorescent compound. Relatively high luminous efficiency can be maintained within the spectral peak -30 nm range.

[0085] However, the peak of the emission spectrum of the exciplex is not the same as the peak of the emission spectrum of the phosphorescent compound. If the wavelength is longer than 1000 nm, the external quantum efficiency of the light-emitting device may decrease. Below, the longest wavelengths of the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound are The overlap with the absorption band located on the side becomes smaller, so the exciplex is converted to the phosphorescent compound. The transfer of excitation energy is difficult, and the exciplex itself converts the excitation energy into light or heat. This is because the enzyme is easily released and becomes inactive.

[0086] Therefore, in order to obtain extremely high luminous efficiency, another aspect of the present invention is to a light-emitting layer including the compound, a first organic compound, and a second organic compound between a pair of electrodes; The first organic compound and the second organic compound are combined to form an exciplex, and the exciplex is The emission spectrum of the complex is located at the longest wavelength side of the absorption spectrum of the phosphorescent compound. The peak wavelength of the emission spectrum of the exciplex overlaps with the absorption spectrum of the phosphorescent compound. The peak wavelength of the absorption band located at the longest wavelength side of the phosphorescent compound is It is a light-emitting element with a wavelength equal to or less than the peak wavelength.

[0087] In the light-emitting element, the peak wavelength of the emission spectrum of the exciplex is equal to the emission spectrum of the phosphorescent compound. Since the wavelength is below the peak wavelength of the electrons, the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound are The overlap with the absorption band at the longest wavelength of the excitation spectrum increases. The excitation energy can be efficiently transferred from the phosphorescent complex to the phosphorescent compound. This allows for suppression of energy deactivation, resulting in low driving voltage and high external quantum efficiency. Therefore, a light emitting device with high light emission can be realized.

[0088] In particular, the peak wavelength of the emission spectrum of the exciplex and the peak wavelength of the emission spectrum of the phosphorescent compound It is preferable that the difference in wavelength is within 30 nm.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] In one embodiment of the present invention, the phosphorescent compound is preferably an organometallic complex.

[0096] The exciplex used in one embodiment of the present invention will be described in detail below.

[0097] <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.

[0098] 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.

[0099] 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 6).

[0100] 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 6 Therefore, the energy difference of the exciplex is the energy difference of the first organic compound, and The energy difference between the first organic compound and the second organic compound is smaller than the energy difference 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.

[0101] The process of forming the exciplex used in one embodiment of the present invention can be roughly divided into two processes.

[0102] ≪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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] The emission spectrum of the formed electroplex was also The wavelengths are longer than those of the organic compounds.

[0108] 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.

[0109] <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.

[0110] 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.

[0111] 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.

[0112] 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...

[0113] This embodiment mode can be combined with other embodiment modes as appropriate.

[0114] (Embodiment 2) In this embodiment, a light-emitting element of one embodiment of the present invention will be described with reference to FIGS.

[0115] FIG. 7A shows a light-emitting device having an EL layer 102 between a first electrode 103 and a second electrode 108. 7A is a diagram showing an element. The light emitting element in FIG. 7A is a diagram showing an element. Layered hole injection layer 701, hole transport layer 702, light emitting layer 703, electron transport layer 704, and electron injection layer The electrode 705 is made up of a first electrode 108 and a second electrode 108 disposed thereon.

[0116] 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.

[0117] 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).

[0118] The first electrode 103 is formed by, for example, sputtering or vapor deposition (including vacuum deposition). It can be achieved.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] The EL layer 102 includes a light-emitting layer 703 and a material having a high hole-injecting property as shown in FIG. a hole injection layer 701 comprising a material with high hole transport properties; a hole transport layer 702 comprising a material with high hole transport properties; The electron transport layer 704 contains a material with high electron transport properties, and the electron injection layer 705 contains a material with high electron injection properties. It is formed by appropriately combining and laminating the child injection layer 705 and the like.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] The light-emitting layer 703 is a layer containing a light-emitting substance. The phosphorescent compound comprises a light-emitting material ( The first organic compound and the second organic compound contained in the light-emitting layer 703 are guest materials. The material that is contained in a larger amount is the host material. do.

[0138] 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)]).

[0139] The first organic compound and the second organic compound are compounds that readily accept electrons (electron transfer compounds). The compound that easily receives holes (hole trapping compound) is combined with a compound that easily receives holes (hole trapping compound). By adopting such a configuration, energy transfer from the exciplex can be prevented. In addition to the effect of improving the luminous efficiency and lifetime due to the The carrier balance is adjusted to improve the luminous efficiency and life span.

[0140] Typical examples of compounds that readily accept electrons include heteroaromatic compounds, such as For example, 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxa Sarin (abbreviation: 2mDBTPDBq-II), 2-[4-(3,6-diphenyl-9H- (carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzP DBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[ f,h]quinoxaline (abbreviation: 7mDBTPDBq-II) and 6-[3-(dibenzyl 6mDB TPDBq-II).

[0141] Compounds that readily accept holes include aromatic amine compounds and carbazoles. Examples of such compounds include 4-phenyl-4'-(9-phenyl-9H-carbazole) 3-[N-(1-naphthyl-3-yl)triphenylamine (abbreviation: PCBA1BP), -N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazol (abbreviation: PCzPCN1), 4,4',4''-tris[N-(1-naphthyl)-N- phenylamino]triphenylamine (abbreviated as 1'-TNATA or 1-TNAT A), 2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]- Spiro-9,9'-bifluorene (abbreviation: DPA2SF), N,N'-bis(9-phenyl) (N,N'-diphenylcarbazol-3-yl)-N,N'-diphenylbenzene-1,3-diamine (abbreviated :PCA2B), N-(9,9-dimethyl-2-N',N'-diphenylamino-9H- Fluoren-7-yl)diphenylamine (abbreviation: DPNF), N,N',N''-triphenylamine Phenyl-N,N',N''-tris(9-phenylcarbazol-3-yl)benzene -1,3,5-triamine (abbreviation: PCA3B), 2-[N-(9-phenylcarbazol- PCA SF), 2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro- 9,9'-Bifluorene (abbreviation: DPASF), N,N'-bis[4-(carbazole- 9-yl)phenyl]-N,N'-diphenyl-9,9-dimethylfluorene-2,7- Diamine (abbreviation: YGA2F), N,N'-bis(3-methylphenyl)-N,N'-diamine Phenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4' -Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation Name: DPAB), N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9, 9-Dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-fluorene- 2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLAD FL), 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]- 9-Phenylcarbazole (abbreviation: PCzPCA1), 3-[N-(4-diphenylamine

[0023] -N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA 1), 3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]- 9-phenylcarbazole (abbreviation: PCzDPA2), 4,4'-bis(N-{4-[N '-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino )biphenyl (abbreviation: DNTPD), 3,6-bis[N-(4-diphenylaminophenyl [1-naphthyl]-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviation: PCzTPN 2), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamine 1-9-phenylcarbazole (abbreviation: PCzPCA2).

[0142] However, the first organic compound and the second organic compound are not limited to these, and may be any compound that can be excited. The combination is capable of forming a complex, and the emission spectrum of the exciplex is such that the absorption spectrum of the phosphorescent compound is The peak of the emission spectrum of the exciplex overlaps with the absorption spectrum of the phosphorescent compound. It is sufficient that the wavelength is longer than the spectral peak.

[0143] The first organic compound is a compound that readily accepts electrons and a compound that readily accepts holes. When the first organic compound and the second organic compound are mixed, the carrier balance can be controlled by the mixing ratio. In other words, the mixing ratio can increase the probability of recombination of holes and electrons in the light-emitting layer, One feature of one embodiment of the present invention is that it is possible to design an optimum balance for increasing the luminous efficiency. From the viewpoint of this carrier balance and the formation of exciplexes, the first It is preferable that the ratio of the first organic compound to the second organic compound is not extremely different. The ratio of the first organic compound to the second organic compound is preferably in the range of 1:9 to 9:1.

[0144] Alternatively, 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.

[0145] 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.

[0146] 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

[0147] 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.

[0148] 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.

[0149] 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.

[0150] As shown in FIG. 7B, the EL layer is formed by disposing a plurality of layers between the first electrode 103 and the second electrode 108. In this case, the first EL layer 800 and the second EL layer 801 are stacked. It is preferable to provide a charge generating layer 803 between the above. 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 laminated structure with a layer made of an electron donating material. A layer containing a substance and a substance having 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. It is difficult to achieve this, and the range of materials to choose from is widened, making it possible to create a light-emitting element that has both high luminous efficiency and a 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.

[0151] 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

[0152] As shown in FIG. 7C, the EL layer 102 is disposed between the first electrode 103 and the second electrode 108. a hole injection layer 701, a hole transport layer 702, a light emitting layer 703, an electron transport layer 704, an electron injection layer The buffer layer 706, the electronic relay layer 707, and the composite material layer 708 in contact with the second electrode 108. 08 may be included.

[0153] 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.

[0154] 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.

[0155] 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).

[0156] 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 various materials can be used to form the substrate.

[0157] 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.

[0158] 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.

[0159] 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 contained in the composite material layer 708 and the LUMO level of the electron transport layer 70 The LUMO level of the highly electron-transporting material contained in 4 is set to be between the LUMO level of the material. The value of the energy level is the L The UMO level is -5.0 eV or higher, preferably -5.0 eV or higher and -3.0 eV or lower. good.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] In this manner, the EL layer 102 of this embodiment can be manufactured.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] In the above manner, a light-emitting element of one embodiment of the present invention can be manufactured.

[0177] 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 manufactured in which the driving of the light-emitting element is controlled by a The light-emitting device can be applied to electronic devices, lighting devices, and the like.

[0178] This embodiment mode can be combined with other embodiment modes as appropriate. [Example]

[0179] 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 FIGS. 1 to 4. explain.

[0180] The phosphorescent compound used in Examples 1 to 4 of this embodiment is (acetylacetonato)bis(4, 6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(a cac)). The first organic compound used in the first to fourth structural examples of this embodiment is 2 -[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (Abbreviation: 2mDBTPDBq-II). The second organic compound used in this example In the structural example 1, 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl ) triphenylamine (abbreviation: PCBA1BP), Example 2 is 3-[N-(1-naphthyl -N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazol (abbreviation: PCzPCN1), and Example 3 is 4,4',4''-tris[N-(1-naphthalene 1'-TNATA, or 1-TNATA), and Example 4 is 2,7-bis[N-(4-diphenylaminophenyl) -N-phenylamino]-spiro-9,9'-bifluorene (abbreviation: DPA2SF) do.

[0181] The chemical formulas of the materials used in this example are shown below.

[0182] [ka]

[0183] (Configuration example 1) Figure 1 shows the emission spectrum (E) of the thin film of the first organic compound, 2mDBTPDBq-II. Optical spectrum 1a), and the emission spectrum of a thin film of the second organic compound, PCBA1BP ( Emission spectrum 2a) and thin film of the mixture of 2mDBTPDBq-II and PCBA1BP The emission spectrum of the film (emission spectrum 3a) is shown. dppm)2(acac)] in dichloromethane solution (hereinafter simply referred to as The absorption spectrum (hereinafter referred to as "absorption spectrum") and emission spectrum (hereinafter referred to as "emission spectrum 4a") are shown.

[0184] In this example, the absorption spectrum of [Ir(dppm)2(acac)] was measured. A UV-visible spectrophotometer (V550 model, manufactured by JASCO Corporation) was used to measure the dichloromethane The solution (0.093 mmol / L) was placed in a quartz cell and measurements were carried out at room temperature.

[0185] In FIG. 1, the horizontal axis represents wavelength (nm) and the vertical axis represents molar absorption coefficient ε (M -1 ·cm - 1 ) and luminescence intensity (arbitrary units).

[0186] From the absorption spectrum in Figure 1, [Ir(dppm)2(acac)] has an absorption peak at around 510 nm. It can be seen that it has a broad absorption band. This absorption band is the one that strongly contributes to the emission. It is thought that this is the case.

[0187] The emission spectrum 3a has a peak at a longer wavelength side than the emission spectra 1a and 2a. The peak of the emission spectrum 3a is closer to the peak of the emission spectrum 1a and the peak of the emission spectrum 2a. From Figure 1, it can be seen that the absorption bands that strongly contribute to the emission of the absorption spectrum are The emission spectrum with the greatest overlap was found to be emission spectrum 3a.

[0188] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBA1BP was It was found that the peak is on the longer wavelength side than the optical spectrum. It is suggested that mixing TPDBq-II and PCBA1BP results in the formation of an exciplex. was done.

[0189] The peak in the emission spectrum 3a is thought to be a strong contributor to the emission in the absorption spectrum. Therefore, it was found that there was a large overlap with the absorption bands of 2mDBTPDBq-II and PCB The light-emitting device using the mixed material of A1BP and [Ir(dppm)2(acac)] Taking advantage of the large overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound It was suggested that the energy transfer efficiency is particularly high. This suggests that a light-emitting device with particularly high external quantum efficiency can be obtained.

[0190] The peak of the emission spectrum 3a is at a longer wavelength than the peak of the absorption spectrum. It is located at a shorter wavelength than the peak of spectrum 4a.

[0191] Since the peak of the emission spectrum of the mixed material is on the long wavelength side, the use of the mixed material It was suggested that a light-emitting element with a low driving voltage could be obtained.

[0192] (Configuration example 2) Figure 2 shows the emission spectrum (E) of the thin film of the first organic compound, 2mDBTPDBq-II. Optical spectrum 1b), and the emission spectrum of a thin film of the second organic compound, PCzPCN1 ( Emission spectrum 2b) and thin film of the mixed material of 2mDBTPDBq-II and PCzPCN1 The emission spectrum of the film (emission spectrum 3b) is shown. Absorption and emission spectra of dichloromethane solution of [(dppm)2(acac)] (Emission spectrum 4b) is shown.

[0193] In FIG. 2, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorption coefficient ε (M -1 ·cm - 1 ) and luminescence intensity (arbitrary units).

[0194] From the absorption spectrum in Figure 2, [Ir(dppm)2(acac)] has an absorption peak at around 510 nm. It can be seen that it has a broad absorption band. This absorption band is the one that strongly contributes to the emission. It is thought that this is the case.

[0195] Emission spectrum 3b has a peak at a longer wavelength side than emission spectra 1b and 2b. Therefore, the emission spectrum of the mixture of 2mDBTPDBq-II and PCzPCN1 is It was found that the peak in the emission spectrum of the 2 By mixing mDBTPDBq-II and PCzPCN1, an exciplex is formed. was suggested.

[0196] In addition, the peak of the emission spectrum 3b overlaps with the absorption spectrum. The mixed material of DBTPDBq-II and PCzPCN1 and [Ir(dppm)2(aca The light-emitting element using the mixed material and the absorption spectrum of the phosphorescent compound Energy transfer is achieved by utilizing the overlap with the electrons, so the energy transfer efficiency is high. Therefore, it was suggested that a light-emitting device with high external quantum efficiency could be obtained.

[0197] The peak of the emission spectrum 3b is at a longer wavelength than the peak of the absorption spectrum. The peak of the emission spectrum 3b is located at a shorter wavelength than the peak of the spectrum 4b. The difference between the peak of the emission spectrum 4b is 21 nm, which is very small.

[0198] Since the peak of the emission spectrum of the mixed material is particularly on the long wavelength side, This suggests that a light-emitting element with a particularly low driving voltage can be obtained.

[0199] (Configuration example 3) Figure 3 shows the emission spectrum (E) of the thin film of the first organic compound, 2mDBTPDBq-II. Optical spectrum 1c), the emission spectrum of a thin film of the second organic compound, 1'-TNATA (Emission spectrum 2c), and the mixed material of 2mDBTPDBq-II and 1'-TNATA The emission spectrum of the thin film of [I Absorption and emission spectra of dichloromethane solution of [r(dppm)2(acac)] The emission spectrum of 4c is shown.

[0200] In FIG. 3, the horizontal axis represents wavelength (nm) and the vertical axis represents molar absorption coefficient ε (M -1 ·cm - 1 ) and luminescence intensity (arbitrary units).

[0201] From the absorption spectrum in Figure 3, [Ir(dppm)2(acac)] has an absorption peak at around 510 nm. It can be seen that it has a broad absorption band. This absorption band is the one that strongly contributes to the emission. It is thought that this is the case.

[0202] Emission spectrum 3c has a peak at a longer wavelength side than emission spectra 1c and 2c. Therefore, the emission spectrum of the mixed material of 2mDBTPDBq-II and 1'-TNATA is It was found that the emission spectrum of the compound has a peak on the longer wavelength side than that of the compound itself. By mixing 2mDBTPDBq-II with 1'-TNATA, an exciplex is formed. It was suggested that...

[0203] In addition, the peak of the emission spectrum 3c overlaps with the absorption spectrum. The mixture of DBTPDBq-II and 1'-TNATA and [Ir(dppm)2(ac The light-emitting element using the mixed material and the absorption spectrum of the phosphorescent compound is Energy transfer is performed using the overlap with the torus, so the energy transfer efficiency is high. Therefore, it was suggested that a light-emitting device with high external quantum efficiency could be obtained.

[0204] In addition, the peak of the emission spectrum 3c is at a longer wavelength than the peak of the absorption spectrum. The peak of emission spectrum 3c is 24 nm away from the peak of emission spectrum 4c. And it's very small.

[0205] In a light-emitting element using the mixed material, the phosphorescent compound begins to emit light due to recombination of carriers. The voltage at which exciplexes are formed by carrier recombination is smaller than the voltage at which exciplexes are formed. In other words, the voltage applied to the light-emitting element is the value at which the phosphorescent compound starts to emit light. Even if the electrons are less than 1000 times as strong as the electrons, the carriers recombine to form exciplexes, allowing current to flow through the light-emitting element. Therefore, it was suggested that a light-emitting device with a particularly low driving voltage could be obtained.

[0206] (Configuration example 4) Figure 4 shows the emission spectrum (E) of the thin film of the first organic compound, 2mDBTPDBq-II. The optical spectrum 1d) and the emission spectrum of the thin film of the second organic compound, DPA2SF ( Optical spectrum 2d) and the thin film of the mixed material of 2mDBTPDBq-II and DPA2SF. The emission spectrum (Emission spectrum 3d) is shown. The absorption and emission spectra of dichloromethane solution of [pm)2(acac)] The optical spectrum 4d) is shown.

[0207] In FIG. 4, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorption coefficient ε (M -1 ·cm - 1 ) and luminescence intensity (arbitrary units).

[0208] From the absorption spectrum in Figure 4, [Ir(dppm)2(acac)] has an absorption peak at around 510 nm. It can be seen that it has a broad absorption band. This absorption band is the one that strongly contributes to the emission. It is thought that this is the case.

[0209] Emission spectrum 3d has a peak at a longer wavelength side than emission spectra 1d and 2d. Therefore, the emission spectrum of the mixture of 2mDBTPDBq-II and DPA2SF is It was found that the emission spectrum of 2m It was shown that exciplexes were formed by mixing DBTPDBq-II and DPA2SF. was suggested.

[0210] In addition, the peak of the emission spectrum 3d overlaps with the absorption spectrum. The mixed material of DBTPDBq-II and DPA2SF and [Ir(dppm)2(acac ) ) is used in a light-emitting element, the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound The energy transfer efficiency is high because the energy transfer is performed by utilizing the overlap with the Therefore, it was suggested that a light-emitting device with high external quantum efficiency could be obtained.

[0211] In addition, the peak of the emission spectrum 3d is at a longer wavelength than the peak of the absorption spectrum. In addition, the difference between the peak of the emission spectrum 3d and the peak of the emission spectrum 4d is 13 nm. And it's very small.

[0212] Since the peak of the emission spectrum of the mixed material is particularly on the long wavelength side, This suggests that a light-emitting element with a particularly low driving voltage can be obtained. [Example]

[0213] 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 are shown below: Note that the chemical formulas of the materials used in the previous examples are omitted.

[0214] [ka]

[0215] A method for fabricating the light-emitting elements 1 to 4 of this example will be described below.

[0216] (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.

[0217] 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.

[0218] 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.

[0219] 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, 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). m, and the mass ratio of DBT3P-II to molybdenum oxide was 1:0.5 (=DBT3 P-II: molybdenum oxide).

[0220] Next, PCBA1BP is formed on the hole injection layer 1111 to a thickness of 20 nm. A hole transport layer 1112 was formed.

[0221] 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 0.7:0.3:0.05 (=2mDBTPDBq-II:PCBA1BP:[I r(dppm)2(acac)]). was set to 40 nm.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] (Light-emitting element 2) The hole transport layer 1112 of the light-emitting element 2 is formed by depositing PCzPCN1 to a thickness of 20 nm. It was formed by

[0227] The light-emitting layer 1113 of the light-emitting element 2 contains 2mDBTPDBq-II, PCzPCN1, and It was formed by co-evaporation of [Ir(dppm)2(acac)]. The weight ratio of PDBq-II, PCzPCN1, and [Ir(dppm)2(acac)] is 0.7:0.3:0.05(=2mDBTPDBq-II:PCzPCN1:[Ir(d The thickness of the light-emitting layer 1113 was adjusted to 40 ppm. The light-emitting element was fabricated in the same manner as the light-emitting element 1 except for the light-emitting layer 1113.

[0228] (Light-emitting element 3) The hole transport layer 1112 of the light-emitting element 3 was formed by depositing 1'-TNATA to a thickness of 20 nm. It was formed by doing this.

[0229] The light-emitting layer 1113 of the light-emitting element 3 contains 2mDBTPDBq-II, 1'-TNATA, and It was formed by co-evaporation of [Ir(dppm)2(acac)] and [Ir(dppm)2(acac)]. Weight ratio of TPDBq-II, 1'-TNATA, and [Ir(dppm)2(acac)] is 0.7:0.3:0.05(=2mDBTPDBq-II:1'-TNATA:[I r(dppm)2(acac)]). The thickness was set to 40 nm. The light-emitting element was fabricated in the same manner as in the light-emitting element 1 except for the light-emitting layer 1113.

[0230] (Light-emitting element 4) The hole transport layer 1112 of the light-emitting element 4 is formed by depositing DPA2SF to a thickness of 20 nm. This was formed by

[0231] The light-emitting layer 1113 of the light-emitting element 4 contains 2mDBTPDBq-II, DPA2SF, and [ The film was formed by co-evaporation of 2mDBTP and Ir(dppm)2(acac). The weight ratio of DBq-II, DPA2SF, and [Ir(dppm)2(acac)] was 0. 7:0.3:0.05(=2mDBTPDBq-II:DPA2SF:[Ir(dppm The thickness of the light-emitting layer 1113 was adjusted to 40 nm. The fabrication was the same as for the light-emitting element 1 except for the light-emitting layer 1113 .

[0232] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0233] The element structures of the thus obtained Light-Emitting Elements 1 to 4 are shown in Table 1.

[0234] [Table 1]

[0235] 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).

[0236] FIG. 9 shows the voltage-luminance characteristics of Light-emitting Elements 1 to 4. In FIG. 9, the horizontal axis represents voltage ( V) and the vertical axis is luminance (cd / m 2 ) and the voltage-current characteristics are shown in Figure 10. At 0, the horizontal axis represents voltage (V) and the vertical axis represents current (mA). The characteristics are shown in Figure 11. In Figure 11, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is power efficiency ( lm / W). The luminance vs. external quantum efficiency characteristics are shown in Figure 12. The axis is luminance (cd / m 2 ) and the vertical axis indicates the external quantum efficiency (%).

[0237] Furthermore, the luminance of light-emitting element 1 to light-emitting element 4 was 1000 cd / m 2 Voltage when near ), 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.

[0238] [Table 2]

[0239] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting elements 1 to 4 are shown in FIG. 13. In FIG. 13, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 2, 1000 cd / m 2 CIE chromaticity coordinates of light-emitting element 1 at luminance of is (x,y)=(0.56,0.44), and the 2 The luminous element at the brightness of The CIE chromaticity coordinates of child 2 are (x,y)=(0.56,0.43), and the brightness is 780 cd / m 2 The CIE chromaticity coordinates of light-emitting element 3 at this luminance are (x, y) = (0.56, 0.43), , 800cd / m 2 The CIE chromaticity coordinates of light-emitting element 4 at a luminance of (x, y) = (0.56 , 0.43). From this result, it can be seen that the light-emitting elements 1 to 4 have an luminance of [Ir(dppm )2(acac)] was observed.

[0240] As can be seen from Table 2, FIGS. 11 and 12, the light-emitting elements 1 to 4 have the following characteristics: current efficiency, The power efficiency and external quantum efficiency were both high.

[0241] In the light-emitting element of this embodiment, the first organic compound, the second organic compound, and the gate electrode shown in Example 1 are used. The light-emitting layer was made of the same material as in Example 1, and the mixture of 2mDBTPDBq-II and the second organic compound was The emission spectrum of the mixed material (emission spectrum of the exciplex) is [Ir(dppm)2 The light-emitting device of this example utilizes this overlap. Because of the energy transfer, it is thought that the energy transfer efficiency is high and the external quantum efficiency is high. do.

[0242] In this example, the light-emitting devices 1, 2, and 4 had higher external quantum efficiency than the light-emitting device 3. (See FIG. 12.) This is because the light-emitting elements 1, 2, and 4 emit light with exciplexes that are weaker than the light-emitting element 3. The absorption spectrum of [Ir(dppm)2(acac)] overlaps significantly with that of [Ir(dppm)2(acac)]. This is thought to be the case (see FIGS. 1 to 4 and Example 1).

[0243] As can be seen from FIGS. 9 and 10, the light-emitting elements 1 to 4 have low light-emission start voltages. The theoretical value of the light emission start voltage of an orange organic EL element is said to be about 2.1 V. It was found that the light-emitting element of one embodiment exhibited a value very close to that.

[0244] In this embodiment, the light-emitting elements 2 to 4 have a lower light-emission start voltage than the light-emitting element 1. This is because the light-emitting elements 2 to 4 are similar to the light-emitting element 1. This is thought to be because the peak of the emission spectrum of the exciplex is located on the longer wavelength side compared to the (See FIGS. 1 to 4 and Example 1).

[0245] 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. Furthermore, by applying one embodiment of the present invention, an element with low driving voltage can be realized. It was shown that this is the case.

[0246] 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).

[0247] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. Driven 4.

[0248] The luminance of the light-emitting element 4 after 260 hours was 93% of the initial luminance. Device 4 was found to be a device with a long life.

[0249] From the above results, by applying one embodiment of the present invention, it is possible to obtain a device with low driving voltage and high reliability. It has been shown that this can be achieved. [Example]

[0250] Example 1 In this example, a light-emitting element of one embodiment of the present invention will be described. The chemical formula is shown below: Note that the chemical formulas of the materials used in the previous examples are omitted.

[0251] [ka]

[0252] [ka]

[0253] [ka]

[0254] The light-emitting elements manufactured in this embodiment are the following structural examples a to s. The device structure is shown in Table 3. The difference between the configuration examples a to s is that the hole transport layer and the light emitting layer The substance X used is the material X in each example configuration. , the HOMO level (eV) of the substance X used in each example, and the shape The emission peak wavelengths (nm) of the exciplexes formed are shown in Table 4. The OMO levels were measured using a photoelectron spectrometer (AC-2, manufactured by Riken Keiki Co., Ltd.).

[0255] [Table 3]

[0256] [Table 4]

[0257] (Configuration example a) The configuration example a is the light-emitting element 1 shown in Example 2. PCBA1BP is used as the substance X. Ta.

[0258] (Configuration example b) Substance X is N,N'-bis(9-phenylcarbazol-3-yl)-N,N'-di Phenylbenzene-1,3-diamine (abbreviation: PCA2B) was used.

[0259] (Configuration example c) Substance X is N-(9,9-dimethyl-2-N',N'-diphenylamino-9H-phenyl)- Diphenylamine (DPNF) was used.

[0260] (Configuration example d) Substance X is N,N',N''-triphenyl-N,N',N''-tris(9-phenyl)- (Nylcarbazol-3-yl)benzene-1,3,5-triamine (abbreviation: PCA3B) was used.

[0261] (Configuration example e) Substance X is 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamine] Spiro-9,9'-bifluorene (abbreviation: PCASF) was used.

[0262] (Configuration example f) Substance X is 2-[N-(4-diphenylaminophenyl)-N-phenylamino]sulfonyl Pyro-9,9'-bifluorene (abbreviation: DPASF) was used.

[0263] (Configuration example g) Substance X is N,N'-bis[4-(carbazol-9-yl)phenyl]-N,N' -Diphenyl-9,9-dimethylfluorene-2,7-diamine (abbreviation: YGA2F) Used.

[0264] (Configuration example h) As substance X, N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1, 1'-biphenyl]-4,4'-diamine (abbreviation: TPD) was used.

[0265] (Configuration example i) Substance X is 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenyl Amino]biphenyl (abbreviation: DPAB) was used.

[0266] (Configuration example j) Substance X is N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9 -dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-fluorene-2 -yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLADF L) was used.

[0267] (Configuration example k) Substance X is 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamine] The compound used was 9-phenylcarbazole (abbreviation: PCzPCA1).

[0268] (Configuration example l) Substance X is 3-[N-(4-diphenylaminophenyl)-N-phenylamino]- 9-phenylcarbazole (abbreviation: PCzDPA1) was used.

[0269] (Configuration example m) Substance X is 3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino] The compound used was [amino]-9-phenylcarbazole (abbreviation: PCzDPA2).

[0270] (Configuration example n) The configuration example n is the light-emitting device 2 shown in Example 2. PCzPCN1 is used as the substance X. Ta.

[0271] (Configuration example o) Substance X is 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'-phenyl]- (phenylamino)phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD) there was.

[0272] (Configuration example p) Substance X is 3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthalene] PCzTPN2 was used.

[0273] (Configuration example q) The configuration example q is the light-emitting element 4 shown in Example 2. DPA2SF was used as the substance X. .

[0274] (Configuration example r) The configuration example r is the light-emitting device 3 shown in Example 2. 1'-TNATA is used as the substance X. there was.

[0275] (Configuration example s) Substance X is 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenyl] The compound used was [9-phenyl-1-amino]-9-phenylcarbazole (abbreviation: PCzPCA2).

[0276] Figure 15 shows the peak wavelength of the emission spectrum of the exciplex in each configuration example and the HOM of substance X. In Fig. 15, the horizontal axis represents the peak wavelength (nm) and the vertical axis represents the HOMO The peaks of the emission spectra of the exciplexes in each configuration example are shown in FIG. In FIG. 16, the horizontal axis represents the peak wavelength (n m), and the vertical axis represents the relative external quantum efficiency (arbitrary unit). The quantum efficiency is shown as a relative value, with the external quantum efficiency of the light-emitting device of configuration example a being set to 1. In FIG. 16, configuration examples e and h are not shown.

[0277] From Figure 15, the higher the HOMO level of substance X, the greater the It was shown that the peak of the emission spectrum of the exciplex formed is on the long wavelength side. Therefore, the higher the HOMO level of substance X, and the closer the peak of the emission spectrum of the exciplex The longer the wavelength, the lower the light emission start voltage of the light emitting element. This allows the driving voltage of the light emitting element to be reduced.

[0278] As can be seen from FIG. 16, if the peak wavelength of the emission spectrum of the exciplex is too long, the external quantum Therefore, the external quantum efficiency is high and the driving voltage is low. To obtain a light-emitting element, there is a preferred range of peak wavelength in the emission spectrum of the exciplex. Specifically, to achieve both low driving voltage and high external quantum efficiency, The peak wavelength of the emission spectrum of the complex is on the longest wavelength side of the absorption spectrum of the phosphorescent compound. The peak wavelength of the absorption band (in this example, approximately 510 nm in the absorption spectrum of the solution) As described above, the peak wavelength of the emission spectrum of the phosphorescent compound (in this example, the EL emission spectrum) It has been suggested that a wavelength of about 580 nm at 1000 kJ / s or less is preferable.

[0279] (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.

[0280] [ka]

[0281] <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.

[0282] [ka]

[0283] 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.

[0284] [ka]

[0285] 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.

[0286] [ka]

[0287] 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

[0288] 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).

[0289] (Reference example 2) The 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[ f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) synthesis method is explained. .

[0290] [ka]

[0291] 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 (b-1).

[0292] [ka]

[0293] 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 poured onto a pad of Celite (Wako Pure Chemical Industries, Ltd.). Industrial Co., Ltd., Catalog No.: 531-16855), Florisil (Wako Pure Chemical Industries, Ltd. The solution was filtered through a filter (Chemical Company, Catalog Number: 540-00135) to obtain a clear, colorless filtrate. The obtained filtrate was concentrated and purified by approximately 700 mL of silica gel column chromatography. Chromatography was carried out using hot toluene as a developing solvent. Acetone and ethanol were added to the mixture, and the mixture was subjected to ultrasonic irradiation. The resulting suspension was then filtered and dried. As a result, 7.85 g of a white powder was obtained in a yield of 80%.

[0294] 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.

[0295] 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%.

[0296] 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.

[0297] 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]

[0298] 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 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 layer including an iridium complex, a first organic compound, and a second organic compound between a pair of electrodes; the first organic compound and the second organic compound are a combination that forms an exciplex, an emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the iridium complex, the peak wavelength of the emission spectrum of the exciplex is equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side in the absorption spectrum of the iridium complex and is equal to or shorter than the peak wavelength of the emission spectrum of the iridium complex, the first organic compound is a heteroaromatic compound; The light-emitting element, wherein the second organic compound is a carbazole compound.

2. a light-emitting layer including an iridium complex, a first organic compound, and a second organic compound between a pair of electrodes; the first organic compound and the second organic compound are a combination that forms an exciplex, an emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the iridium complex, the peak wavelength of the emission spectrum of the exciplex is equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side in the absorption spectrum of the iridium complex and is equal to or shorter than the peak wavelength of the emission spectrum of the iridium complex, a difference between a peak wavelength of the emission spectrum of the exciplex and a peak wavelength of the emission spectrum of the iridium complex is 30 nm or less; the first organic compound is a heteroaromatic compound; The light-emitting element, wherein the second organic compound is a carbazole compound.

3. a light-emitting layer including an iridium complex, a first organic compound, and a second organic compound between a pair of electrodes; the first organic compound and the second organic compound are a combination that forms an exciplex, an emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the iridium complex, the peak wavelength of the emission spectrum of the exciplex is equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side in the absorption spectrum of the iridium complex and is equal to or shorter than the peak wavelength of the emission spectrum of the iridium complex, the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound, 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 with a higher level.

4. a light-emitting layer including an iridium complex, a first organic compound, and a second organic compound between a pair of electrodes; the first organic compound and the second organic compound are a combination that forms an exciplex, an emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the iridium complex, the peak wavelength of the emission spectrum of the exciplex is equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side in the absorption spectrum of the iridium complex and is equal to or shorter than the peak wavelength of the emission spectrum of the iridium complex, a difference between a peak wavelength of the emission spectrum of the exciplex and a peak wavelength of the emission spectrum of the iridium complex is 30 nm or less; the first organic compound is a heteroaromatic compound; the second organic compound is a carbazole compound, 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 with a higher level.

5. In any one of claims 1 to 4, A hole transport layer is provided. The hole transport layer comprises an aromatic amine compound.

6. In any one of claims 1 to 4, A hole transport layer is provided. The hole transport layer comprises an aromatic amine compound having a fluorenyl group.

7. In any one of claims 1 to 4, A hole transport layer is provided. The hole transport layer contains an aromatic amine compound having a spiro-9,9'-bifluorene group.

8. In any one of claims 1 to 7, an electron transport layer; The light-emitting device, wherein the electron transport layer comprises a second heteroaromatic compound.

9. In any one of claims 1 to 7, The light-emitting element has a first electron transport layer and a second electron transport layer between the pair of electrodes.

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

11. A lighting device comprising the light-emitting device according to claim 10.

12. An electronic device comprising the light emitting device according to claim 10.

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