Light emitting element

Abstract

To provide a light-emitting element with high luminous efficiency or long life, which contains a smaller amount of a phosphorescent compound.SOLUTION: A light-emitting element includes, between a pair of electrodes, a light-emitting layer including a phosphorescent compound, a first organic compound, and a second organic compound. The first organic compound and the second organic compound are combination forming an excitation complex (exciplex). The light-emitting element causes energy transfer by using overlapping between a light emission spectrum of the excitation complex and an absorption spectrum of the phosphorescent compound; therefore, energy transfer efficiency is high even if concentration of the phosphorescent compound is low.SELECTED DRAWING: None

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 has been actively carried out (Patent Document 1, Patent Document 2 and Non-Patent Document 3). The basic structure of an organic EL element is a pair of electrodes between which a light-emitting organic compound is placed. This allows for a thin and lightweight structure and high sensitivity to input signals. Due to its characteristics such as fast response and low DC voltage drive, it is expected to be the next generation flat panel display. It is attracting attention as a display element.

[0003] Furthermore, displays using such light-emitting elements have excellent contrast and image quality, and have a wide viewing angle. In addition, since organic EL elements are surface light sources, they are much lighter than LCDs. Applications as a light source for backlighting and illumination for play are also being considered.

[0004] The light-emitting mechanism of organic EL elements is the carrier injection type. In other words, the light-emitting layer is sandwiched between electrodes. By applying a voltage, the electrons and holes injected from the electrodes recombine and The luminescent material becomes excited and emits light when the excited state returns to the ground state. The types of states include singlet excited states (S * ) and triplet excited states (T * ) is possible. The statistical generation ratio of the light-emitting element is S * :T * = 1:3 is.

[0005] Light-emitting organic compounds usually have a singlet ground state. Therefore, the singlet excited state (S * ) is an electron transition between atoms of the same spin multiplicity and is called fluorescence. Triplet excited state (T * ) is an electron transition between different spin multiplicities, and is called phosphorescence. Generally, a compound that emits fluorescence (hereafter referred to as a fluorescent compound) emits phosphorescence at room temperature. Therefore, in the case of a light-emitting device using a fluorescent compound, only fluorescence is observed, and no photoinduced ... The theoretical limit of the internal quantum efficiency (the ratio of photons generated to the injected carriers) is S * :T * It is said to be 25% based on the ratio of 1:3.

[0006] On the other hand, if a compound that emits phosphorescence (hereinafter referred to as a phosphorescent compound) is used, the internal quantum It is possible to increase the efficiency up to 100%. In other words, it has a higher luminescence efficiency than fluorescent compounds. For this reason, in order to realize a highly efficient light emitting device, In recent years, the development of light-emitting devices using phosphorescent compounds has been actively pursued. As for compounds, organometallic compounds with iridium as the central metal are popular due to their high phosphorescence quantum efficiency. For example, Patent Document 1 describes an organometallic complex having iridium as the central metal. Metal complexes have been disclosed as phosphorescent materials.

[0007] When the light-emitting layer of the light-emitting element is formed using the above-mentioned phosphorescent compound, the concentration of the phosphorescent compound is extinct. In order to suppress quenching by light and triplet-triplet annihilation, In this case, the phosphorescent compound is often dispersed in the matrix. The compound is the host, and the compound dispersed in the matrix, such as the phosphorescent compound, is the guest (or is called a dopant.

[0008] In addition, in Patent Document 2 or Non-Patent Document 1, the light-emitting layer is made of a material with good electron transport properties and a material with good hole transport properties. For example, Non-Patent Document 1 states that Tris-8-quinolinolatoaluminum complex (Alq3) with good transport properties and hole transport 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl ( The two materials are NPB and methylquinacridone as a guest (dopant). A light-emitting device using mqa (abbreviation: mqa) has been proposed.

[0009] In the light-emitting layer with this structure, two types of hosts each take on different functions, and both electrons and holes are In other words, electrons are conducted through Alq3, and holes are conducted through NP B, both of which reach mqa, which can be excited. mqa is However, in Patent Document 2, a phosphorescent compound is used as a guest to emit triple fluorescence. It is disclosed that light emission can be obtained from the first excited state. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2000 / 070655 [Patent Document 2] U.S. Patent No. 7,572,522 [Non-patent literature]

[0011] [Non-Patent Document 1] Vi-En Choong et al. “Organic light-emitting diodes with a bipolar transport layer”, Appl. Phys. Lett., 75, 172 (1999). Summary of the Invention [Problem to be solved by the invention]

[0012] Iridium is a rare element (Clark number 1×10 -7 %), which is more expensive than iridium. (Clark number 5 x 10 -7 %), Gold (Clark number 5 x 10 -7 %) buried near the surface The amount of this substance used is small. For this reason, there are concerns about its stable supply, and there are calls to reduce its use. can be.

[0013] However, in general, when a phosphorescent compound is used as a guest, excessively decreasing the concentration of the guest This can be explained as follows. There are two possible processes for this. First, electrons and holes are injected into the guest molecule. The other is a direct recombination process in which the guest molecule is excited by the excitation of the This is an energy transfer process in which the state of the host molecule is transferred to the guest molecule.

[0014] To increase the rate of direct recombination, the guest must be present in high concentration. As the guest concentration decreases, the recombination probability decreases, and the luminescence efficiency decreases.

[0015] On the other hand, there are two mechanisms for the energy transfer process: the Förster mechanism and the Dexter mechanism. The theory has been proposed.

[0016] The Förster mechanism does not require direct contact between molecules for energy transfer, but is a mechanism in which the host molecule and that energy transfer occurs through the resonance phenomenon of dipole vibration between guest molecules. The host molecule transfers energy to the guest molecule through the resonance phenomenon of dipole vibration. , the host molecule reaches the ground state and the guest molecule reaches the excited state. The rate of the Förster mechanism Constant k h * →g is shown in Equation (1).

[0017]

number

[0018] In formula (1), ν represents the frequency, and f' h (ν) is the normalized Emission spectrum (fluorescence spectrum when discussing energy transfer from a singlet excited state, When discussing energy transfer from a triplet excited state, 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 excitation state represents the lifetime of the photoelectron state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, and φ represents the luminescence quantum efficiency (single When discussing energy transfer from single excited states, the fluorescence quantum efficiency is used. When discussing energy transfer from triplet excited states, the fluorescence quantum efficiency is used. When discussing energy transfer, it stands for phosphorescence quantum efficiency, and K 2 is the host molecule and 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.

[0019] The Dexter mechanism occurs when the host and guest molecules approach the effective contact distance where orbitals overlap. The 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 is k h * →g Formula (2) As shown in.

[0020]

number

[0021] In formula (2), h is the Planck constant, and K is a constant with the dimension of energy. where ν is the frequency and f' is the h (ν) is the normalized emission spectrum of the host molecule (When discussing energy transfer from a singlet excited state, use the fluorescence spectrum, and when discussing energy transfer from a triplet excited state, use the 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.

[0022] In general, the distance at which energy can be transferred by the Dexter mechanism is about 1 nm, and The maximum distance that energy can be transferred by the star mechanism is thought to be about 10 nm. As a result, the concentration of the guest decreases and the distance between the guest molecule and the excited host molecule increases. If the guest concentration is increased, the efficiency of energy transfer drops significantly. It has been deemed essential that

[0023] As described above, the elementary process from carrier recombination to the formation of the excited state of the guest Considering this, it is necessary to increase the guest concentration in order to efficiently excite the guest. However, when the guest is highly concentrated, the luminescence efficiency decreases due to the aggregation of the guest. This leads to a decrease in the amount of ionized light, i.e., concentration quenching, so the excited state of the guest can be efficiently generated. However, the luminous efficiency of the device will decrease as a result. The efficiency of generating excited states of the guest becomes poor, and concentration quenching occurs at high guest concentrations. However, there was a dilemma that either way, the luminous efficiency would decrease.

[0024] In view of the above, one aspect of the present invention is to provide a novel light-emitting mechanism that can be used to obtain a more natural light-emitting device. Another object of the present invention is to provide a light-emitting element in which the concentration of fluorine is reduced. Another object of the present invention is to provide a light-emitting device having a long life. Another object of the present invention is to provide a light-emitting device that is less susceptible to deterioration. Another object of one embodiment of the present invention is to provide a highly reliable light-emitting device. One aspect of the present invention achieves at least one of the above-mentioned objects. [Means for solving the problem]

[0025] One aspect of the present invention is a light-emitting device comprising a phosphorescent compound, a first organic compound, and a second organic compound. A layer is disposed between a pair of electrodes, and a first organic compound and a second organic compound form an exciplex. The phosphorescence intensity is determined by the sum of the weights of the first organic compound and the second organic compound. The weight ratio of the mixture is 0.1% or more and 2.5% or less, preferably 0.1% or more and 1.5% or less. More preferably, the light-emitting element has a content of 0.1% or more and 0.5% or less.

[0026] Further, one embodiment of the present invention is a light-emitting diode 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 at least one first organic compound and at least one The second organic compound is a combination that forms an exciplex, and the exciplex is a phosphorescent compound. The phosphorescent compound emits phosphorescence, and the weight ratio of the first organic compound and the second organic compound is The weight ratio of the phosphorescent compound to the sum of the above is 0.1% or more and 2.5% or less, preferably 0. The light-emitting element has a refractive index of 1% or more and 1.5% or less, and more preferably 0.1% or more and 0.5% or less. .

[0027] Further, one embodiment of the present invention is a light-emitting diode 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 the first organic compound or the second organic compound is a single layer. An exciplex is formed between a first organic compound and a second organic compound from a first exciton. The ratio of the weight of the phosphorescent compound to the sum of the weights of the first organic compound and the second organic compound is , 0.1% or more and 2.5% or less, preferably 0.1% or more and 1.5% or less, more preferably 0 It is a light-emitting element having a refractive index of 0.1% or more and 0.5% or less.

[0028] Further, one embodiment of the present invention is a light-emitting diode 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 the first organic compound and the second organic compound are The anion of the compound and the cation of the second organic compound are used to form a first organic compound and a second organic compound. The compound exciplex is formed, and the weight ratio of the first organic compound and the second organic compound is The weight ratio of the phosphorescent compound to the sum of the above is 0.1% or more and 2.5% or less, preferably 0. The light-emitting element has a refractive index of 1% or more and 1.5% or less, and more preferably 0.1% or more and 0.5% or less. .

[0029] In the light-emitting element, the excitation energy of the exciplex is transferred to the phosphorescent compound, Preferably the compound is phosphorescent.

[0030] 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.

[0031] In the light-emitting element, the phosphorescent compound is an organometallic complex having iridium. preferable.

[0032] In the light-emitting device, the molar ratio of the phosphorescent compound at the peak of the emission spectrum of the exciplex is Absorption coefficient is 5000M -1 cm -1 More preferably, it is equal to or greater than this.

[0033] In the light-emitting element, the first organic compound has an electron-transporting property higher than a hole-transporting property. The second organic compound preferably has a hole-transporting property higher than an electron-transporting property.

[0034] The light-emitting element of one embodiment of the present invention can be applied to light-emitting devices, electronic devices, and lighting devices. do. Effect of the Invention

[0035] In the above-mentioned energy transfer process, the efficiency of energy transfer from the host molecule to the guest molecule Φ ET It is considered that k can be expressed by the formula (3). r is the emission process of the host molecule (host Fluorescence is the energy transfer from the singlet excited state of a molecule, and triplet excited state of a host molecule. When discussing energy transfer from an excited state, k represents the rate constant of phosphorescence, n is a non-luminous represents the rate constant of the process (thermal deactivation and intersystem crossing), and τ represents the lifetime of the excited state of the host molecule measured. Represents life.

[0036]

number

[0037] From equation (3), the energy transfer efficiency Φ ET To increase the rate of energy transfer, Constant k h * →g , other competing rate constants k r +k n (=1 / τ) is much larger than Then, the rate constant of the energy transfer, k h * →g Make it bigger In order to do this, it is necessary to determine whether the mechanism is the Förster mechanism or the Dexter mechanism from formulas (1) and (2). In these mechanisms, the emission spectrum of the host molecule (energy transfer from the singlet excited state) Fluorescence spectra are used to discuss the energy transfer from triplet excited states. It was found that it is better to have a large overlap between the phosphorescence spectrum and the absorption spectrum of the guest molecule. do.

[0038] In addition, the higher the absorptivity of the guest molecule at the peak of the emission spectrum of the host molecule, the This indicates that the energy transfer process from the molecule to the guest molecule is likely to occur.

[0039] That is, the excited state energy level of the host molecule and the excited state energy of the guest molecule The levels are set to be nearly equal, and the probability of transition to an excited state of the guest molecule is increased. This makes it easier for energy to transfer.

[0040] However, under these conditions, when the host is a single material as in the conventional case, the excitation The process of energy transfer from the excited guest molecule to the ground host molecule also becomes easier. As a result, the luminous efficiency decreases.

[0041] This problem can be solved by using exciplexes, which will be explained in detail here. An exciplex is an excited state complex between different molecules. The exciplex is formed by the interaction of two electrons. The exciplex is a relatively deep lowest unoccupied molecular orbital (LUMO:Lo Materials with west unoccupied molecular orbital levels Materials and shallow highest occupied molecular orbitals (HOMOs) It is generally known that the formation of a lattice structure between materials with a crystalline orbital level is easy. It is being done.

[0042] 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 level of the organic compound is related to the

[0043] Even if this condition is met, the exciplex is not necessarily formed. In the literature, no exciplex can be formed between Alq3 and NPB. Please note that if this is not possible, the following effects cannot be obtained.

[0044] When an exciplex is formed by the first organic compound and the second organic compound, the LU of the exciplex is The MO level comes from the first organic compound, and the HOMO level comes from the second organic compound. Therefore, the energy difference of the exciplex is the energy difference of the first organic compound and the second organic compound. The energy difference between the first and second organic compounds is smaller than that between the first and second organic compounds. The emission wavelength of the exciplex is longer than that of each of the compounds.

[0045] The process of exciplex formation can be roughly divided into the following two processes. This is due to the formation of an electroplex. A cycloplex is a compound consisting of a first organic compound in the ground state and a second organic compound in the ground state. Specifically, the anion of the first organic compound is directly converted into an exciplex. When the cation of a second organic compound is adjacent to the cation of the first organic compound, the two form an exciplex.

[0046] From the above relationship, the first organic compound is an electron trapping compound, and the second organic compound Since is a hole-trapping compound, the anion of the first organic compound and the anion of the second organic compound An electroplex is formed directly from the cation of the substance.

[0047] The emission spectrum of the electroplex formed was determined by the first organic compound and the second organic compound. The emission wavelengths of these compounds are longer than those of the other compounds.

[0048] 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 with each other. The light-emitting element according to one embodiment of the present invention is an electroplex. By utilizing the overlap of the emission spectrum of the source and the absorption spectrum of the guest phosphorescent compound, Therefore, the energy transfer efficiency is high. In this case, a light emitting device with high external quantum efficiency can be realized.

[0049] As mentioned above, in general, when an electron and a hole recombine in a host, the host is in an excited state. Excitation energy is transferred from the molecule to the guest molecule, causing the guest molecule to reach an excited state and emit light. .

[0050] Here, before the excitation energy is transferred from the host molecule to the guest molecule, the host molecule itself The excitation energy is reduced by emitting light at unintended wavelengths or by converting the excitation energy into heat energy. In particular, when the host molecule is in a singlet excited state, The excitation lifetime is shorter than that of the triplet excited state, so singlet excitons are less likely to deactivate. The deactivation of excitons is one of the factors that leads to a decrease in the lifetime of light-emitting elements.

[0051] On the other hand, 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), the excited It is possible to suppress the formation of short singlet excitons. There may be a process in which the exciplex is formed directly without the need for the singlet exciton quenching. Therefore, a light emitting element having a long life can be realized.

[0052] In this way, the generation of the singlet excited state of the host is suppressed, and the guest is released from the electroplex. The concept of obtaining a light-emitting element with high luminous efficiency by transferring energy to a terbium molecule has never been seen before. .

[0053] In another process, one of the first organic compound and the second organic compound serving as a host is After forming a singlet exciton, the elementary process in which it interacts with another in the ground state to form an exciplex is Unlike electroplexes, in this case, the singlet excitons of the host However, this is quickly converted to an exciplex, so it is still a singlet exciton. Deactivation can be suppressed.

[0054] The experimental results described below also show that the singlet excitons in the host are rapidly converted into exciplexes. It is clear that the inactivation of the host can be suppressed. According to one embodiment of the present invention, a light-emitting element with a long lifetime can be achieved.

[0055] In this case, the emission spectrum of the exciplex formed is also similar to that of the first organic compound and the second organic compound. The wavelengths of the organic compounds are longer than those of the organic compounds.

[0056] Also in this case, the emission spectrum and phosphorescence of the first organic compound (or the second organic compound) are The emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound overlap rather than overlapping with each other. The light-emitting element of one embodiment of the present invention has an emission spectrum of an exciplex. Energy transfer is achieved by utilizing the overlap between the light spectrum and the absorption spectrum of the phosphorescent compound. Therefore, in one embodiment of the present invention, the external quantum efficiency Therefore, a light emitting element with high light emission efficiency can be realized.

[0057] In addition, from the above relationship, the first organic compound is an electron trapping compound, while the second organic compound is an electron trapping compound. The above organic compounds are hole-trapping compounds. The difference in the HOMO levels of these compounds, and When the difference between the LUMO level and the LUMO level is large (specifically, the difference is 0.3 eV or more), the electron preferentially The electron preferentially enters the first organic compound and the hole preferentially enters the second organic compound. The process of forming an electroplex is more important than the process of forming an exciplex via an excitation electron. It is considered that priority will be given to the above.

[0058] By the way, the concept that an energy level exists only in an excited state of an exciplex is valid. Therefore, in the ground state, the molecules that compose the exciplex consist of two or more independent molecules, and these molecules do not form any complexes in the ground state.

[0059] For example, energy is transferred from an excited exciplex to a guest molecule in the ground state, resulting in a guest If a molecule is excited, even if the guest molecule tries to excite other molecules, In one embodiment, the molecule to be excited is a first organic compound or a second organic compound. And to excite the first organic compound or the second organic compound, The guest molecules do not have enough energy to be excited in their excited states.

[0060] In other words, the excited state of the guest molecule undergoes reverse energy transfer to the exciplex. In principle, the phenomenon in which guest molecules are deactivated before they can emit light (i.e., the emission efficiency is reduced) This is also one of the reasons why the luminous efficiency can be increased.

[0061] As described above, in one embodiment of the present invention, an energy transfer between an excited state and a ground state of a molecule is performed. It is preferable to make the energy difference between the excited states of the exciplex almost equal. The excited energy levels of the first organic compound and the guest are almost equal. The excited energy levels of the compound and the second organic compound are higher than the excited energy levels of the exciplex. It will become more expensive.

[0062] That is, the guest molecule in the excited state excites the first organic compound and the second organic compound. However, there is not enough energy to transfer the energy from the guest molecule to another molecule. Therefore, the light emission efficiency is improved in one embodiment of the present invention. Since thermal deactivation can be suppressed, the life of the light-emitting element can be extended, deterioration can be suppressed, and reliability can be improved.

[0063] As described above, the singlet exciton of the first organic compound or the second organic compound is converted into an exciplex. That is, one of the first organic compound and the second organic compound may form a A compound that forms a singlet exciton and then interacts with another in the ground state to form an exciplex. And this process is thought to occur very quickly.

[0064] Since singlet excitons have a short excitation lifetime (τ is small), the excitation is usually from the singlet excitons of the host. Before the excitation energy is transferred to the guest, some of the excitation energy is lost (unwanted). The problem is that the photon emission is at a wavelength that is too short or is thermally deactivated (Φ ET Is small tends to happen.)

[0065] However, in one embodiment of the present invention, the singlet excitons of the host rapidly form an exciplex. This suppresses the deactivation of the exciplex. Because of its long length, the energy transfer efficiency Φ ET Therefore, it is expected that the The suppression of the deactivation of singlet excitons in the host, which is thought to affect not only the efficiency but also the lifetime of the electrons, Therefore, a light emitting element having a long life can be realized.

[0066] In addition, the excitation energy of the exciplex is sufficiently transferred to the phosphorescent compound, and the It is preferred that substantially no emission from the device is observed. Transferring energy through the body to a phosphorescent compound, causing the phosphorescent compound to emit phosphorescence. is preferred.

[0067] In addition, from the above-mentioned concept of energy transfer, the first organic compound and the second organic compound At least one of the compounds is a fluorescent compound (i.e., a compound that emits light or undergoes thermal deactivation from a singlet excited state). Therefore, the first organic compound and the second organic compound are effective when the first organic compound and the second organic compound are easily reacted with each other. It is preferred that at least one of the organic compounds is a fluorescent compound.

[0068] The organic compound used as the host (the first organic compound and / or the second organic compound) When a phosphorescent compound is used, the organic compound itself becomes more likely to emit light, and energy is transferred to the guest. In this case, it is sufficient if the organic compound emits light efficiently, but However, it is difficult to achieve high luminous efficiency with these organic compounds because of the problem of concentration quenching. Therefore, a fluorescent compound is used as the organic compound, and the above-mentioned structure is used to obtain energy. It is preferable to move.

[0069] The above-mentioned effect is due to the formation of an exciplex between the first organic compound and the second organic compound. For example, in the method described in Non-Patent Document 1, an exciplex is formed. Therefore, the guest molecule can only be excited by a direct recombination process, and the emission efficiency is not sufficient. It's not too expensive.

[0070] In general, when exciplexes are used in the light-emitting layer of a light-emitting device, they have the advantage of being able to control the color of emitted light. However, the luminescence efficiency is usually significantly reduced. Optical elements have traditionally been considered unsuitable for achieving highly efficient light emitting elements.

[0071] However, as shown in one embodiment of the present invention, the energy transfer from the exciplex to a phosphorescent compound is The inventors have found that by using the material as a moving medium, the luminous efficiency can be increased to the limit. This is a technological concept that contradicts conventional stereotypes.

[0072] In one embodiment of the present invention, the excitation energy level of the exciplex and the energy of the excited state of the guest are The energy levels are set to be nearly equal, and the probability of transition to an excited state of the guest is increased. This increases the probability of the energy transfer process. % or more and 2.5% or less, preferably 0.1% or more and 1.5% or less, more preferably 0.1% or less Even at a concentration of 0.5% or less, sufficient energy transfer can be achieved. Since concentration quenching can be suppressed, the luminous efficiency can be maximized. [Brief description of the drawings]

[0073] [Figure 1] 1A and 1B illustrate light-emitting elements according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows an absorption spectrum and an emission spectrum according to Example 1. [Diagram 3]FIG. 11 shows an absorption spectrum and an emission spectrum according to Example 2. [Figure 4] FIG. 13 is a graph showing current density-luminance characteristics of a light-emitting element according to Example 3. [Diagram 5] FIG. 13 is a graph showing voltage-luminance characteristics of a light-emitting element according to Example 3. [Figure 6] FIG. 13 is a graph showing voltage-current characteristics of a light-emitting element according to Example 3. [Figure 7] FIG. 13 is a graph showing luminance-chromaticity characteristics of a light-emitting element according to Example 3. [Figure 8] FIG. 11 is a graph showing luminance-current efficiency of a light-emitting element according to Example 3. [Figure 9] FIG. 11 is a graph showing the luminance-power efficiency of the light-emitting element according to Example 3. [Figure 10] FIG. 11 is a graph showing the luminance-external quantum efficiency characteristics of the light-emitting element according to Example 3. [Figure 11] FIG. 13 shows an emission spectrum of the light-emitting element according to Example 3. [Figure 12] FIG. 13 is a graph showing current density-luminance characteristics of a light-emitting element according to Example 4. [Figure 13] FIG. 13 is a graph showing voltage-luminance characteristics of a light-emitting element according to Example 4. [Figure 14] FIG. 13 is a graph showing voltage-current characteristics of a light-emitting element according to Example 4. [Figure 15] FIG. 13 is a graph showing luminance-chromaticity characteristics of a light-emitting element according to Example 4. [Figure 16] FIG. 13 is a graph showing luminance-current efficiency of a light-emitting element according to Example 4. [Figure 17] FIG. 13 is a graph showing the luminance-power efficiency of a light-emitting element according to Example 4. [Figure 18] FIG. 13 is a graph showing the luminance-external quantum efficiency characteristics of the light-emitting element according to Example 4. [Figure 19] FIG. 13 shows an emission spectrum of a light-emitting element according to Example 4. [Figure 20] FIG. 13 is a graph showing current density-luminance characteristics of a light-emitting element according to Example 5. [Figure 21] FIG. 13 is a graph showing voltage-luminance characteristics of a light-emitting element according to Example 5. [Figure 22] FIG. 13 is a graph showing voltage-current characteristics of a light-emitting element according to Example 5. [Diagram 23] FIG. 13 is a graph showing luminance-chromaticity characteristics of a light-emitting element according to Example 5. [Figure 24] FIG. 13 is a graph showing luminance-current efficiency of a light-emitting element according to Example 5. [Diagram 25] FIG. 13 is a graph showing the luminance-power efficiency of the light-emitting element according to Example 5. [Figure 26] FIG. 13 is a graph showing the luminance-external quantum efficiency characteristics of the light-emitting element according to Example 5. [Figure 27] FIG. 13 is a graph showing luminance vs. external energy efficiency characteristics of a light-emitting element according to Example 5. [Figure 28] FIG. 13 shows an emission spectrum of the light-emitting element according to Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0074] The embodiment 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 embodiment, and various changes and modifications may be made in the form and details without departing from the spirit and scope of the present invention. It will be easily understood by those skilled in the art that the above-mentioned invention can be obtained by the following embodiments. The present invention should not be construed as being limited to the contents described below. The same reference numerals are used in different drawings to indicate the same parts or parts having similar functions. A repeated explanation thereof will be omitted.

[0075] (Embodiment 1) In this embodiment, a light-emitting element according to one embodiment of the present invention will be described. The light-emitting layer of the device contains a guest, which is a light-emitting substance, and a host in which the guest is dispersed. In the present study, a phosphorescent compound was used as a guest, and a first organic compound and a second organic compound were used as hosts. The first organic compound and the second organic compound form an exciplex. It's a combination.

[0076] In the present embodiment, the triplet excited energies of the organic compounds used as hosts are Energy level (T * Ranking) is guest T * It is preferable that the level of the host is higher than the T * The guest is T * If the triplet excitation energy of the guest is lower than the level, the emission This is because the host quenches the light emitted by the organic EL element, resulting in a decrease in luminous efficiency.

[0077] As mentioned above, the guest's T * The T level of the exciplex * If you want to make it almost equal to the level , Guest T * The level is the T of the first organic compound (or the second organic compound). * Lower than the level Therefore, in many cases, this problem can be overcome.

[0078] The first organic compound and the second organic compound that constitute the host form an exciplex. When the exciplex emits light, the emission wavelength is determined by the ratio of the first organic compound to the second organic compound. The emission wavelength (fluorescence wavelength) of each of these compounds is longer than that of the other compounds. By forming the first organic compound, the fluorescence spectrum of the second organic compound can be obtained. The emission spectrum can be converted to one that is located at longer wavelengths.

[0079] Therefore, if the fluorescence spectrum of the first organic compound (or the second organic compound) is The absorption band of the phosphorescent compound is located on the shorter wavelength side than the absorption band located on the longest wavelength side, and Even if there is no overlap, the formation of an exciplex can shift the fluorescence spectrum to a longer wavelength. It is possible to convert the emission spectrum to a larger overlap with the absorption band.

[0080] The light-emitting element of the present embodiment has an emission spectrum of the exciplex and an absorption spectrum of the phosphorescent compound. The energy transfer from the exciplex to the phosphorescent compound is achieved by utilizing the overlap with the torus. The concentration of the guest is 0.1% or more and 2.5% or less, preferably 0.1% or more and 1.5% or less, more preferably Even if the concentration is preferably 0.1% or more and 0.5% or less, sufficient energy transfer efficiency can be obtained. .

[0081] In order to fully overlap the emission spectrum of the exciplex with the absorption spectrum of the guest, The energy value of the peak in the optical spectrum and the lowest energy absorption band in the absorption spectrum It is preferable that the difference between the energy value of the peak of is within 0.3 eV. It is within 0.2 eV, and most preferably within 0.1 eV.

[0082] The light-emitting element of this embodiment will be described with reference to FIG.

[0083] FIG. 1A shows a light-emitting device having an EL layer 102 between a first electrode 101 and a second electrode 103. The light-emitting element in FIG. 1(A) is a diagram showing a light-emitting element. A hole injection layer 111, a hole transport layer 112, a light emitting layer 113, an electron transport layer 114, and an electron injection layer 115 are laminated. The semiconductor device is composed of an insulating layer 115 and a second electrode 103 provided thereon.

[0084] The first electrode 101 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, indium oxide-zinc oxide, tungsten oxide containing silicon oxide Examples include indium oxide containing stainless steel and zinc oxide (IWZO).

[0085] These conductive metal oxide films are usually formed by sputtering, but they can also be formed by sol-gel deposition. For example, an indium oxide-zinc oxide film can be fabricated by applying the indium oxide method. Sputtering method using a target containing 1 to 20 wt% zinc oxide indium The IWZO film can be formed by the following method. The target contained 0.5-5 wt% zinc and 0.1-1 wt% zinc oxide. It can be formed by a pulverizing method.

[0086] Other metals include graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, iron, and copper. ballast, copper, palladium, or nitrides of metallic materials (e.g., titanium nitride), etc. .

[0087] However, the layer of the EL layer 102 formed in contact with the first electrode 101 is an organic compound as 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 101 may be any of various metals, alloys, and the like, regardless of the magnitude of the work function. Electrically conductive compounds and mixtures thereof can be used. For example, aluminum Aluminum, silver, and alloys containing aluminum (eg, Al--Si) can also be used.

[0088] The first electrode 101 is formed by, for example, a sputtering method or a deposition method (including a vacuum deposition method). It can be achieved.

[0089] The second electrode 103 is made of a metal, an alloy, or an electric field 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. Specifically, An element in group 1 or 2 of the periodic table, i.e. an alkali such as lithium or cesium Alkaline earth metals such as calcium and strontium, magnesium, and alloys containing these (e.g., Mg-Ag, Al-Li), europium, ytterbium In addition to rare earth metals such as nickel and alloys containing these, aluminum and silver can also be used. Cut.

[0090] However, the layer of the EL layer 102 formed in contact with the second electrode 103 is an organic compound as described later. When a composite material made by mixing a compound and an electron donor is used, the work function is large. Indium oxide containing Al, Ag, ITO, silicon or silicon oxide, regardless of size A variety of conductive materials can be used, such as tin oxide.

[0091] In addition, when forming the second electrode 103, a vacuum deposition method or a sputtering method is used. In addition, when using silver paste, the coating method or the inkjet method can be used. It can be used.

[0092] The EL layer 102 includes at least a light-emitting layer 113. It is also possible to use either a low molecular weight compound or a high molecular weight compound. The material for forming the EL layer 102 is not limited to organic compounds. This also includes configurations that partially contain inorganic compounds.

[0093] The EL layer 102 includes a light-emitting layer 113 and a material having a high hole-injecting property as shown in FIG. the hole transport layer 112 containing a material with high hole transport properties; The electron transport layer 114 includes a material having a high electron transporting property, and the electron It is formed by appropriately combining and laminating the child injection layer 115 and the like.

[0094] The hole-injection layer 111 is a layer containing a substance with high hole-injection properties. 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.

[0095] 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 (abbreviation: DNTP D) 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamine 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.

[0096] Furthermore, polymeric compounds (oligomers, dendrimers, polymers, etc.) can also be used. For example, poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltrifluoroethylene) phenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenyl phenyl-N'-phenylamino}phenyl)methacrylamide (abbreviation: PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bi Examples of polymer compounds include poly(phenyl)benzidine (abbreviation: Poly-TPD). In addition, poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS), polyaniline / poly(styrenesulfonic acid) (PAni / PS A polymer compound to which an acid such as dimethylaminoethyl ether (S) is added can be used.

[0097] The hole injection layer 111 is formed by mixing an organic compound and an electron acceptor. Such a composite material 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 is.

[0098] 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 compound having a low molecular weight. -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 the composite material are described. The compounds are specifically listed below.

[0099] 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 P) and other 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-carbazolyl) Carbazole derivatives such as [2,3,5,6-tetraphenylbenzene]-2,3,5,6-zolylphenyl can be used.

[0100] 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, etc. An aromatic hydrocarbon compound can be used.

[0101] 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, an Thracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-bu (ethyl)perylene, pentacene, coronene, 4,4'-bis(2,2-diphenylvinyl) Biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl) It is possible to use aromatic hydrocarbon compounds such as diphenylanthracene (DPVPA). can.

[0102] In addition, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroethylene is used as an electron acceptor. Organic compounds such as fluoroquinodimethane (abbreviation: F4-TCNQ), 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, etc. 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 weight. It is preferred because it has low moisture content and is easy to handle.

[0103] In addition, the above-mentioned polymer compounds such as PVK, PVTPA, PTPDMA, and Poly-TPD A composite material may be formed using the above-mentioned electron acceptor and used for the hole injection layer 111.

[0104] The hole-transporting layer 112 is a layer containing a substance having a high hole-transporting property. The following are examples of 4,4'-bis[N-(9,9-dimethylfluorophenyl) 4,4-Diphenyl-2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), '-Bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino] An aromatic amine compound such as biphenyl (abbreviation: BSPB) can be used. The substances mentioned are mainly 10 -6 cm 2 / Vs or more. Any other substance may be used as long as it has a higher hole transporting property than an electron transporting property. The layer containing a substance having a high hole-transporting property may be a single layer or may be a layer having two or more layers of the above substance. It may be laminated on top.

[0105] The hole transport layer 112 may also include a carbazole derivative such as CBP, CzPA, or PCzPA. Anthracene derivatives such as t-BuDNA, DNA, and DPAnth may also be used. stomach.

[0106] The hole transport layer 112 may be formed of a material such as PVK, PVTPA, PTPDMA, or Poly-TPD. Any polymeric compound can be used.

[0107] The light-emitting layer 113 is a layer containing a light-emitting substance. The light-emitting device has a phosphorescent compound as a host, and a first organic compound and a second organic compound as a host. Two or more types of hosts can be used. The total weight of the hosts (the host is the first organic compound and The ratio of the weight of the guest to the weight of the first organic compound (the sum of their weights in the case of the first organic compound and the second organic compound) is 0.1 % or more and 2.5% or less, preferably 0.1% or more and 1.5% or less, more preferably 0.1% or less The upper limit shall be 0.5% or less.

[0108] As the phosphorescent compound, an organometallic complex is preferable, and an iridium complex is particularly preferable. Considering the energy transfer by the Förster mechanism described above, the longest wavelength of phosphorescent compounds is The molar extinction 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.

[0109] An example of a compound having such a large molar absorption coefficient is bis(3,5-dimethyl (2-phenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]), (acetylacetonato)bis(4,6-di Phenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac )]), (acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinium dinato]iridium(III) (abbreviation: [Ir(nbppm)2(acac)]), (2 ,6-Dimethyl-3,5-heptanedionato-κ 2 O,O')bis[4-methyl-2-( 3-Methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III) (abbreviation :[Ir(5mdppm)2(dibm)]), (acetylacetonato)bis(2-phenyl Nildibenzo[f,h]quinoxalinato)iridium(III) (abbreviation: [Ir(dbq In particular, [Ir(dppm)2(acac)] ], the molar extinction coefficient is 5000M -1 ·cm -1 If materials that reach above this level are used, A light-emitting device with a partial quantum efficiency of approximately 30% can be obtained.

[0110] Examples of the first organic compound and the second organic compound include 2-[3-(dibenzothiophene) 2m-phenyl-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDB q-II), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl 1,2-Dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-( Dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7 mDBTPDBq-II) and 6-[3-(dibenzothiophen-4-yl)phenyl 6mDBTPDBq-II and 4,4'-bis[N-(1-naphthyl)- N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), 4-phenyl-4 '-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PC BA1BP), and 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H- Carbazol-3-yl)triphenylamine (abbreviation: PCBNBB) It is preferable to combine it with any one of the easily-receiving compounds. There are no particular limitations to these combinations, and any combination that can form an exciplex may be used.

[0111] 2mDBTPDBq-II, PCBNBB, and the phosphorescent compound used when using these [Ir(dppm)2(acac)], [Ir(mppr-Me)2(dpm) The main physical properties of ] are as shown in Table 1.

[0112] [Table 1]

[0113] In the light-emitting layer 113 in which 2mDBTPDBq-II and PCBNBB are mixed, the LUMO level is -2.78 eV, and the HOMO level is -5.46 eV. The LUMO and HOMO levels of the exciplex of q-II and PCBNBB are the same. And , the LUMO level of the phosphorescent compound [Ir(mppr-Me)2(dpm)], and the HOM The O levels are also at the same level.

[0114] On the other hand, the LUMO and HOMO levels of [Ir(dppm)2(acac)] are both Since the charge transport coefficient is lower than that of [Ir(dppm)2(acac)], it is easy to trap electrons. Therefore, when [Ir(dppm)2(acac)] is used as a phosphorescent compound, The probability of the direct recombination process is higher than that of [Ir(mppr-Me)2(dpm)]. This suggests that the

[0115] Also, [Ir(mppr-Me)2(dpm)] is also [Ir(dppm)2(acac)] The triplet excited state energy level (T * Level) is 2mDBTPDBq-II and PCBN BB's T * Since it is 0.1 electron volts lower than the level of [Ir(mppr-Me)2(d After [Ir(dppm)2(acac)] and [Ir(dppm)2(acac)] enter a triplet excited state, The probability of energy transfer to the triplet excited state of 2mDBTPDBq-II and PCBNBB is small. In particular, [Ir(dppm)2(acac)] is 0.18 eV lower. This suggests that [Ir(dppm)2(acac)] has a higher luminous efficiency.

[0116] The electron-transporting layer 114 is a layer containing a substance with a high electron-transporting property. The following is a list of Alq3, tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Alm q3), Bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq 2), BAlq, Zn(BOX)2, bis[2-(2-hydroxyphenyl)benzothiazolidinyl] Zolato]zinc (abbreviation: 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-triphenyl TAZ (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl) p-EtTA Z), Bathophenanthroline (abbreviation: BPhen), Bathocuproine (abbreviation: 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 2,2'-bipyridine-6,6'-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 / Vs or higher. Any substance other than the above may be used for the electron transport layer as long as it has a higher electron transporting property than the above. stomach.

[0117] The electron transport layer may be a single layer or a laminate of two or more layers of the above-mentioned materials. It may also be possible to use the following.

[0118] The electron injection layer 115 is a layer containing a substance with high electron injection properties. fluoride, cesium, calcium, lithium fluoride, cesium fluoride, calcium fluoride, Uses alkali metals, alkaline earth metals, or compounds thereof, such as lithium oxide, etc. Also, rare earth metal compounds such as erbium fluoride can be used. Moreover, the above-mentioned materials for forming the electron transport layer 114 can also be used.

[0119] Alternatively, the electron injection layer 115 may be a composite material made by mixing an organic compound and an electron donor. Such composite materials are made by adding electrons to an organic compound by an electron donor. Therefore, it has excellent electron injection and electron transport properties.

[0120] In this case, the organic compound is preferably a material that is excellent in transporting the generated electrons. Specifically, for example, the above-mentioned substance constituting the electron transport layer 114 (metal complex or heteroaromatic Compounds, etc.) can be used.

[0121] The electron donor may be any substance that exhibits electron donating properties to organic compounds. , alkali metals, alkaline earth metals and rare earth metals are preferred, and lithium, cesium, magnesium Nesium, calcium, erbium, ytterbium, etc. Metal oxides and alkaline earth metal oxides are preferred, and lithium oxide, calcium oxide, barium oxide, etc. In addition, Lewis bases such as magnesium oxide can be used. It is also possible to use organic compounds such as tetrathiafulvalene (TTF). can.

[0122] The hole injection layer 111, the hole transport layer 112, the light emitting layer 113, and the electron transport layer 114 The electron injection layer 115 is formed by a deposition method (including a vacuum deposition method), an inkjet method, a coating method, and the like, respectively. It can be formed by a method such as a cloth method.

[0123] As shown in FIG. 1B, the EL layer is formed by disposing a plurality of layers between the first electrode 101 and the second electrode 103. In this case, the first EL layer 104 and the second EL layer 105 are stacked. It is preferable to provide a charge generating layer 106 between the above. The charge generating layer 106 is the above-mentioned composite. The material may be formed.

[0124] The charge generating layer 106 may also have a laminated structure of a layer made of a composite material and a layer made of another material. In this case, the layer made of the other material may be a layer made of an electron donating material and a material having high electron transport properties. A layer containing a conductive material, a layer made of a transparent conductive film, or the like can be used.

[0125] A light-emitting element having such a configuration is less susceptible to problems such as energy transfer and quenching. By expanding the range of materials to be selected, it will be possible to develop light-emitting devices that have both high luminous efficiency and a long lifespan. 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 EL layer structure described above.

[0126] In addition, by making the emission color of each EL layer different, the light-emitting device as a whole can have a desired color. For example, in a light-emitting element having two EL layers, the first By making the emission color of the first EL layer and the emission 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

[0127] As shown in FIG. 1C, the EL layer 102 is disposed between the first electrode 101 and the second electrode 103. a hole injection layer 111, a hole transport layer 112, a light emitting layer 113, an electron transport layer 114, an electron injection layer 115, a hole transport layer 116, a hole injection layer 117, a hole transport layer 118, a light emitting layer 119, a hole transport layer 119, a hole injection layer 110, a hole transport layer 111, a light emitting layer 112, a light emitting layer 1 The buffer layer 116, the electronic relay layer 117, and the composite layer 1 in contact with the second electrode 103 18 may be included.

[0128] By providing the composite material layer 118 in contact with the second electrode 103, it is possible to form a thin film by using a sputtering method. Therefore, when the second electrode 103 is formed, damage to the EL layer 102 can be reduced. The composite material layer 118 is preferably made of the above-mentioned organic compound having a high hole transporting property. Composite materials containing receptor substances can be used.

[0129] Furthermore, by providing an electron injection buffer layer 116, the composite material layer 118 and the electron transport layer 1 Since the injection barrier between the composite material layer 118 and the electrode 14 can be reduced, the electrons generated in the composite material layer 118 can be injected into the electrode 14. The electron transport layer 114 can be easily injected with the electrons.

[0130] The electron injection buffer layer 116 may include an element selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, and and their compounds (alkali metal compounds (oxides such as lithium oxide, halides, carbonates, etc.) (including carbonates such as lithium and cesium carbonate), alkaline earth metal compounds (oxides, halides, etc.) compounds of rare earth metals (including oxides, halides, carbonates) It is possible to use a substance having a high electron injection property such as tetrahydrofuran (TFA) or the like.

[0131] In addition, the electron injection buffer layer 116 is formed by containing a material having high electron transport properties and a donor material. In the case where the compound is formed, the mass ratio of the compound 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 a ratio of

[0132] The donor substance may be an alkali metal, an alkaline earth metal, a rare earth metal, or the like. These compounds (alkali metal compounds (oxides such as lithium oxide, halides, lithium carbonate, etc.) Alkaline earth metal compounds (including oxides, halides, etc.) compounds of rare earth metals (including oxides, halides, carbonates) )), tetrathianaphthacene (abbreviation: TTN), nickelocene, decamethylnickelocene, Organic compounds such as benzene can also be used.

[0133] As the substance having a high electron transporting property, the same material as the material of the electron transport layer 114 described above can be used. It can be formed using materials.

[0134] Furthermore, an electron relay layer 117 is provided between the electron injection buffer layer 116 and the composite material layer 118. The electron relay layer 117 is not necessarily required, but it is preferable to form the electron relay layer 117. By providing the electron relay layer 117 with high transportability, electrons can be transferred to the electron injection buffer layer 116. This makes it possible to send it quickly.

[0135] An electron relay layer 117 is sandwiched between the composite layer 118 and the electron injection buffer layer 116. The structure is composed of an acceptor material contained in a composite material layer 118 and an electron injection buffer layer 11. The structure is such that it is difficult for the donor substance contained in 6 to interact with each other and inhibit each other's functions. Therefore, an increase in the driving voltage can be prevented.

[0136] The electron relay layer 117 contains a material with high electron transport properties, and the LUM of the material with high electron transport properties The O level is determined by the LUMO level of the acceptor material contained in the composite material layer 118 and the electron transport The electron transport layer 114 is formed so as to have a LUMO level between the LUMO level of the material having high electron transport properties contained in the layer 114 .

[0137] In addition, when the electron relay layer 117 contains a donor material, the donor equivalent of the donor material is The LUMO level of the acceptor material in the layer 118 and the electron transport layer 114 The LUMO level of the material with high electron transport properties is set to be between the LUMO level of the material with high electron transport properties. The energy level of the material with high electron transport properties contained in the electron relay layer 117 is expressed as the LU value. The MO level is set to -5.0 eV or more, preferably -5.0 eV or more and -3.0 eV or less. stomach.

[0138] The electron relay layer 117 may contain a phthalocyanine-based material or a highly electron-transporting material. It is preferable to use a metal complex having a metal-oxygen bond and an aromatic ligand.

[0139] Specific examples of the phthalocyanine-based material contained in the electron relay layer 117 include CuPc, SnPc (Phthalocyanine tin(II) complex), ZnP c(Phthalocyanine zinc complex), CoPc(Coba lt(II)phthalocyanine, β-form), FePc(Phtha locyanine Iron) and PhO-VOPc(Vanadyl 2,9,16 ,23-tetraphenoxy-29H,31H-phthalocyanine) It is preferable to use either one of the above.

[0140] The metal complexes having a metal-oxygen bond and an aromatic ligand contained in the electron relay layer 117 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), and electron transfer (donation and receipt) is facilitated. In addition, metal complexes with metal-oxygen double bonds are considered to be stable. Therefore, by using a metal complex having a metal-oxygen double bond, it is possible to obtain a light-emitting element having a low This makes it possible to drive the device more stably with a voltage.

[0141] As the 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 mplex) is a molecular structure in which the metal-oxygen double bond acts on other molecules. This is preferred because it is easy to do and has a high acceptor property.

[0142] As the above-mentioned phthalocyanine-based material, those having a phenoxy group are preferable. 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. In addition, since it is soluble in a solvent, This has the advantage that maintenance of the device used for film formation becomes easier.

[0143] The electron relay layer 117 may further include 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) ), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth 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 substances in the electron relay layer 117, the electron This facilitates movement, and enables the light-emitting element to be driven at a lower voltage.

[0144] When the electron-relay layer 117 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 118 is Materials with high LUMO levels can be used.

[0145] A specific energy level is -5.0 eV or more, preferably -5.0 eV or more to -3. It is preferable to use a substance that has a LUMO level in the range of 0.0 eV or less. Examples of the substance include perylene derivatives and nitrogen-containing condensed aromatic compounds. The nitrogen-containing condensed aromatic compound is stable and is therefore suitable for use in forming the electron relay layer 117. It is a preferred material for this purpose.

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

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

[0148] In addition, 7,7,8,8-tetracyanoquinodimethane (TCNQ), 1,4, 5,8-Naphthalenetetracarboxylic dianhydride (abbreviation: NTCDA), Perfluorinated pentafluoropentane 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 (abbreviation: NTCD)-1,4,5,8-naphthalenetetracarboxylic acid diimide I-C8F), 3',4'-dibutyl-5,5''-bis(dicyanomethylene)-5,5 ''-Dihydro-2,2':5',2''-terthiophene) (abbreviation: DCMT), meta Nonofullerenes (e.g., [6,6]-phenyl C 61 Butyric acid methyl ester, etc. This can be done.

[0149] When the electron-relay layer 117 contains a donor substance, the donor substance is a substance having a high electron transporting property. The electron relay layer 117 may be formed by a method such as co-evaporation with an insulating material.

[0150] The hole injection layer 111, the hole transport layer 112, the light emitting layer 113, and the electron transport layer 114 are made of the above-mentioned materials. Each can be formed using the same material.

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

[0152] The light-emitting element described above emits a light emitting diode (LED) by a potential difference generated between the first electrode 101 and the second electrode 103. A current flows, and holes and electrons recombine in the EL layer 102, causing light to be emitted. This light emission is generated by either the first electrode 101 or the second electrode 103 or both. Therefore, the electric current is taken out to the outside through either the first electrode 101 or the second electrode 103. Either or both of the electrodes are transparent to visible light.

[0153] The structure of the layers provided between the first electrode 101 and the second electrode 103 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 101 and the second electrode 103. Any configuration other than the above may be used as long as it provides regions.

[0154] In other words, the layer stack structure is not particularly limited, and a substance having a high electron transporting property, a substance having a high hole transporting property, high electron injection, high hole injection, bipolar materials (electron and A layer made of a material with high hole transport properties, or a hole blocking material, etc., can be freely combined with the light-emitting layer. It is sufficient to combine them to configure the system.

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

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

[0157] In this example, a first organic compound that can be used for a light-emitting element of one embodiment of the present invention, An example of a combination of a second organic compound and a phosphorescent compound will be described with reference to FIG. 2. .

[0158] The phosphorescent compound used in this example is bis(3,5-dimethyl-2-phenylpyrazine). (Dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2( dpm)]). The first organic compound used in this example is 2-[3-(diphenyl ether) 2mDibenzo[f,h]quinoxaline (abbreviation: 2mDB The second organic compound used in this example is 4,4'-diphenyl ether (TPDBq-II). (1-Naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenyl The chemical formulas of the above materials are shown below.

[0159] [ka]

[0160] <Absorption spectrum> FIG. 2(A) and FIG. 2(B) show the phosphorescent compound [Ir(mppr-Me)2(dpm The ultraviolet-visible absorption spectrum (absorption spectrum A) of a dichloromethane solution of The spectrum was measured using an ultraviolet-visible spectrophotometer (V550, manufactured by JASCO Corporation). The dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were performed at room temperature. I did.

[0161] <Emission spectrum> Also, FIG. 2(A) and FIG. 2(B) show the first organic compound, 2mDBTPDB. Emission spectrum of the thin film of q-II (Emission spectrum 1), the second organic compound, PCB Emission spectrum of the thin film of NBB (Emission spectrum 2), and 2mDBTPDBq-II and The emission spectrum of the thin film of the PCBNBB mixed material (Emission spectrum 3) is shown in Figure 2(A). ), the horizontal axis indicates wavelength (nm) and the vertical axis indicates molar extinction coefficient ε (M -1 ·cm -1 ) and emission intensity (arbitrary unit). In FIG. 2(B), the horizontal axis represents energy (eV) The vertical axis represents the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary unit) .

[0162] From the absorption spectrum A in Figure 2(A), [Ir(mppr-Me)2(dpm)] is 50 It can be seen that the fluorine-containing compound has a broad absorption band around 0 nm. This absorption band strongly contributes to the emission of light. It is believed that this is an absorption band.

[0163] Emission spectrum 3 has a peak on the longer wavelength (lower energy) side than emission spectra 1 and 2. The peak of the emission spectrum 3 is smaller than the peaks of the emission spectra 1 and 2. , which is located close to the absorption band. The emission spectrum that overlaps most with the absorption band that strongly contributes to the emission of Specifically, the peak of absorption spectrum A and the peak of emission spectrum 3 The peak difference was 0.10 eV.

[0164] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBNBB is It was found that the spectrum had a peak on the longer wavelength (lower energy) side. Therefore, by mixing 2mDBTPDBq-II and PCBNBB, an exciplex was formed. It was suggested that this is the case.

[0165] The emission spectrum of the mixed material is similar to the absorption spectrum of [Ir(mppr-Me)2(dpm)]. It was found that there is a large overlap with the absorption band that is thought to strongly contribute to the luminescence at 1000 .mu.m. Therefore, the mixed material of 2mDBTPDBq-II and PCBNBB was used as the host, [Ir(mpp The light-emitting device using the guest Zn(r-Me)2(dpm) has the emission spectrum of the mixed material. Energy transfer is achieved by utilizing the overlap with the absorption spectrum of the phosphorescent compound. This suggests that the energy transfer efficiency is high. Therefore, a light-emitting device with high external quantum efficiency can be obtained. It was suggested that this could be done. EXAMPLES

[0166] In this example, a first organic compound that can be used for a light-emitting element of one embodiment of the present invention, An example of a combination of a second organic compound and a phosphorescent compound will be described with reference to FIG. 3. .

[0167] The phosphorescent compound used in this example is (acetylacetonato)bis(4,6-diphenylpyridine). iridium(III) (abbreviation: [Ir(dppm)2(acac)]) The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is PCBNBB. Materials used in this example The chemical formula of the material shown in Example 1 is shown below.

[0168] [ka]

[0169] <Absorption spectrum> Figure 3(A) and Figure 3(B) show the phosphorescent compound [Ir(dppm)2(acac)] The ultraviolet-visible absorption spectrum (absorption spectrum B) of the dichloromethane solution of The spectra were measured using an ultraviolet-visible spectrophotometer (V550, manufactured by JASCO Corporation). The dichloromethane solution (0.093 mmol / L) was placed in a quartz cell and measurements were performed at room temperature. .

[0170] <Emission spectrum> Also, in FIG. 3(A) and FIG. 3(B), the first organic compound, 2mDBTPDB Emission spectrum of the thin film of q-II (emission spectrum 4), the second organic compound, PCB Emission spectrum of the thin film of NBB (Emission spectrum 5), and 2mDBTPDBq-II and The emission spectrum of the thin film of the PCBNBB mixed material (Emission spectrum 6) is shown in Figure 3(A). ), the horizontal axis indicates wavelength (nm) and the vertical axis indicates molar extinction coefficient ε (M -1 ·cm -1 ) and emission intensity (arbitrary unit). In FIG. 3(B), the horizontal axis represents energy (eV) The vertical axis represents the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary unit) .

[0171] From the absorption spectrum B of Fig. 3(A), [Ir(dppm)2(acac)] is It can be seen that the absorption band is broad around m. This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a collection.

[0172] Emission spectrum 6 has a peak on the longer wavelength (lower energy) side than emission spectra 4 and 5. The peak of the emission spectrum 6 is smaller than the peaks of the emission spectra 4 and 5. , which is located close to the absorption band. The emission spectrum with the largest overlap with the absorption band that strongly contributes to the emission of Specifically, the peak of absorption spectrum B and the peak of emission spectrum 6 The peak difference was 0.02 eV.

[0173] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBNBB is It was found that the spectrum had a peak on the longer wavelength (lower energy) side. Therefore, by mixing 2mDBTPDBq-II and PCBNBB, an exciplex was formed. It was suggested that this is the case.

[0174] The emission spectrum peak of the mixed material corresponds to the absorption spectrum of [Ir(dppm)2(acac)]. It was found that the spectrum overlaps with the absorption band that is thought to strongly contribute to the emission. The molar extinction coefficient is also 5000M -1 ·cm -1 That's all. Therefore, 2mDBTP The mixed material of DBq-II and PCBNBB was used as the host, [Ir(dppm)2(acac)] The light-emitting element using the mixed material as a guest has a spectrum similar to that of the phosphorescent compound. Energy transfer is highly efficient because it utilizes the overlap with the torus. Furthermore, it is expected that sufficient energy transfer will occur even at low guest concentrations. Cut. EXAMPLES

[0175] In this example, a phosphorescent compound, an organometallic complex, (acetylacetonato)bis[4-( 2-norbornyl)-6-phenylpyrimidinato)]iridium(III) (abbreviation: [I In a light-emitting device using a guest, The properties were investigated by increasing and decreasing the concentration. The structure of [Ir(nbppm)2(acac)] is shown below. As shown in.

[0176] [ka]

[0177] The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is 4-phenyl-4'-(9-phenyl-9H-carbazolyl) The compound is PCBA1BP (abbreviation: PCBA1BP). The combination of mDBTPDBq-II and PCBA1BP was As with the combination of q-II and PCBNBB, an exciplex is formed, and the emission spectrum of The position is also roughly the same as in the first embodiment.

[0178] In this example, light-emitting elements 1, 2, and 3 were fabricated, each of which has a different concentration of guest. The structures of the light-emitting elements 1, 2, and 3 are shown in FIG. 1(A). The structural formula of the organic compound used in this example is shown below. Excluding those that have been

[0179] [ka]

[0180] First, a silicon-containing insulator film having a thickness of 110 nm was prepared as the first electrode 101 functioning as an anode. A glass substrate with an indium tin oxide (ITSO) film was prepared. The ITSO surface was 2 μm thick. The periphery is covered with a polyimide film so that the surface is exposed, with an electrode area of ​​2 mm × 2 m. As a pretreatment for forming a light-emitting element on this substrate, the substrate surface was washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0181] Then, 10 -4 In the heating chamber of a vacuum deposition device where the inside was decompressed to about 170 Pa, After vacuum baking at ℃ for 30 minutes, the substrate was allowed to cool for about 30 minutes. The substrate was fixed to a holder installed in the deposition chamber of the vacuum deposition apparatus so that the coated surface was facing downward. It was determined.

[0182] The deposition chamber was -4 After depressurizing to 100 Pa, 1,3,5-tri(dibenzothiophene-4-yl) )-benzene (abbreviation: DBT3P-II) and molybdenum(VI) oxide, II: Molybdenum oxide = 4:2 (weight ratio) by co-evaporation to inject holes A layer 111 was formed. The thickness of the layer was set to 40 nm. This is a deposition method in which two materials are evaporated simultaneously from different evaporation sources.

[0183] Next, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine A hole transport layer 112 was formed by depositing 20 nm of BPAFLP (abbreviation: BPAFLP).

[0184] Further, on the hole transport layer 112, 2mDBTPDBq-II, PCBA1BP, and [I r(nbppm)2(acac)], 2mDBTPDBq-II:PCBA1BP:[ Ir(nbppm)2(acac)] = 0.8:0.2:x (weight ratio) The light-emitting layer 113 was formed by co-evaporation of x=0. For light-emitting element 2, x was set to 0.025, and for light-emitting element 3, x was set to 0.05.

[0185] Next, 10 nm of 2mDBTPDBq-II was added, followed by bathophenanthroline (abbreviation: BP The electron transport layer 114 was formed by depositing 20 nm of hexafluorophenyl ether. In the example, the electron transport layer 114 is a 10 nm thick first electron transport layer of 2mDBTPDBq-II. layer and a second electron transport layer of BPhen with a thickness of 20 nm.

[0186] Furthermore, lithium fluoride is deposited on the electron transport layer 114 to a thickness of 1 nm. The electron injection layer 115 was formed. Thus, the EL layer 102 was formed. In all cases, the deposition was performed using a resistance heating method.

[0187] Finally, an aluminum film is formed to a thickness of 200 nm as the second electrode 103 that functions as a cathode. The light-emitting element was completed. The layer structure of the light-emitting element is shown in Table 2. In the table, x represents the layer structure of the light-emitting element. For light emitting element 1, it is 0.01, for light emitting element 2, it is 0.025, and for light emitting element 3, it is 0.05.

[0188] [Table 2]

[0189] The light-emitting elements (light-emitting elements 1 to 3) obtained as described above were placed in a globe in a nitrogen atmosphere. The process of sealing the light-emitting element in the box so that it is not exposed to the atmosphere (the temperature is kept at 80°C during sealing). After performing a heat treatment for 1 hour at 400 K for 1 hour, the operating characteristics of these light-emitting devices were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0190] FIG. 4 shows the current density vs. luminance characteristics of the light-emitting elements 1 to 3. In FIG. d / m 2 ), the horizontal axis is the current density (mA / cm 2 ) are shown. The voltage-luminance characteristics of the 1000-nm CMOS sensor are shown in Fig. 5. In Fig. 5, the vertical axis indicates the luminance (cd / m 2 ), the horizontal axis is voltage (V) FIG. 6 shows the voltage-current characteristics of the light-emitting elements 1 to 3. In FIG. 6, the vertical axis indicates the current The abscissa represents the chromaticity-luminance characteristics of the light-emitting elements 1 to 3. In Fig. 7, the vertical axis is chromaticity and the horizontal axis is luminance (cd / m 2 ) is shown.

[0191] FIG. 8 shows the current efficiency vs. luminance characteristics of the light-emitting elements 1 to 3. In FIG. 8, the vertical axis indicates the current efficiency (cd / A), the horizontal axis is luminance (cd / m 2 The power efficiencies of the light-emitting elements 1 to 3 are shown. The efficiency-luminance characteristics are shown in Fig. 9. In Fig. 9, the vertical axis shows power efficiency (lm / W) and the horizontal axis shows luminance (cd / m 2 10 shows external quantum efficiency vs. luminance characteristics of Light-emitting Elements 1 to 3. In Fig. 10, the vertical axis represents external quantum efficiency (%) and the horizontal axis represents luminance (cd / m 2 ) Light-emitting element 1 The emission spectrum of the light-emitting element 3 is shown in FIG. 11. In FIG. 11, the vertical axis represents the emission intensity (arbitrary unit). The horizontal axis indicates wavelength (nm).

[0192] In addition, in FIG. 4 to FIG. 11, LE1 represents light-emitting element 1, LE2 represents light-emitting element 2, and LE3 represents light-emitting element 3. indicates the light-emitting element 3.

[0193] 4 to 11, the light-emitting element 1, which has a lower concentration of guest, emits more light than the light-emitting elements 2 and 3. It can be seen that the light efficiency is high. Table 3 shows the main characteristics of the light-emitting elements 1 to 3. In the table, LE1 indicates light-emitting element 1, LE2 indicates light-emitting element 2, and LE3 indicates light-emitting element 3. As can be seen from Fig. 3, in the light-emitting device 1 in which the weight ratio of the guest to the total weight of the host is 1%, Even if there is a guest, the light-emitting element 2 and the light-emitting element 3, which have a higher weight ratio of the guest, have better characteristics. It was discovered that...

[0194] [Table 3] EXAMPLES

[0195] In this embodiment, a phosphorescent compound, an organometallic complex (2,6-dimethyl-3,5-hepta ndionate-κ 2 O,O')bis[4-methyl-2-(3-methyl-4-pyrimidinyl- [Ir(5mdppm)2(d In a light-emitting device using ZnO (Si) as a guest, the characteristics were changed by increasing or decreasing the concentration of the guest. The structure of [Ir(5mdppm)2(dibm)] is shown below.

[0196] [ka]

[0197] The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is 4,4'-bis[N-(1-naphthyl)-N-phenyl] The structural formula of NPB is shown below. The combination of 2mDBTPDBq-II and NPB formed an exciplex as in Example 1. The position of the emission spectrum is also roughly the same as in Example 1.

[0198] [ka]

[0199] In this example, light-emitting elements 4, 5, and 6 were fabricated, each of which has a different concentration of guest. The structures of the light-emitting elements 4, 5, and 6 are shown in FIG. This shows that.

[0200] First, a silicon-containing insulator film having a thickness of 110 nm was prepared as the first electrode 101 functioning as an anode. A glass substrate with an indium tin oxide (ITSO) film was prepared. The ITSO surface was 2 μm thick. The periphery is covered with a polyimide film so that the surface is exposed, and the electrode area is 2 mm × 2 m. As a pretreatment for forming a light-emitting element on this substrate, the substrate surface was washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0201] Then, 10 -4 In the heating chamber of a vacuum deposition device where the inside was decompressed to about 170 Pa, After vacuum baking at ℃ for 30 minutes, the substrate was allowed to cool for about 30 minutes. The substrate was fixed to a holder installed in the deposition chamber of the vacuum deposition apparatus so that the coated surface was facing downward. It was determined.

[0202] The deposition chamber was -4 After reducing the pressure to 10 Pa, DBT3P-II and molybdenum(VI) oxide were DBT3P-II:molybdenum oxide = 4:2 (weight ratio) Thus, a hole injection layer 111 was formed. The film thickness was set to 40 nm.

[0203] Subsequently, BPAFLP was evaporated to a thickness of 20 nm to form a hole transport layer 112 .

[0204] Further, on the hole transport layer 112, 2mDBTPDBq-II, NPB, and [Ir(5md ppm)2(dibm)], 2mDBTPDBq-II:NPB:[Ir(5mdpp m)2(dibm)] = 0.8:0.2:x (weight ratio) In this manner, the light-emitting layer 113 was formed. For light-emitting element 5, x was set to 0.025, and for light-emitting element 6, x was set to 0.05.

[0205] Next, 10 nm of 2mDBTPDBq-II was evaporated, followed by 20 nm of BPhen. The electron transport layer 114 was formed by the above-mentioned method. Further, lithium fluoride was deposited on the electron transport layer 114 by 1000 nm. The electron injection layer 115 was formed by vapor deposition so that the thickness of the EL layer 10 was 1 nm. 2 was formed. In the above-mentioned deposition processes, the deposition was all performed using a resistance heating method.

[0206] Finally, an aluminum film is formed to a thickness of 200 nm as the second electrode 103 that functions as a cathode. The light-emitting element was completed. The layer structure of the light-emitting element is shown in Table 4. In the table, x represents the number of layers of the light-emitting element. For light emitting element 4, it is 0.01, for light emitting element 5, it is 0.025, and for light emitting element 6, it is 0.05.

[0207] [Table 4]

[0208] The light-emitting elements (light-emitting elements 4 to 6) obtained in the above manner were placed in a globe in a nitrogen atmosphere. The process of sealing the light-emitting element in the box so that it is not exposed to the atmosphere (the temperature is kept at 80°C during sealing). After performing a heat treatment for 1 hour at 400 K for 1 hour, the operating characteristics of these light-emitting devices were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0209] FIG. 12 shows current density-luminance characteristics of the light-emitting elements 4 to 6. In FIG. 12, the vertical axis indicates luminance (cd / m 2 ), the horizontal axis is the current density (mA / cm 2 In addition, light-emitting element 4 to light-emitting element The voltage-luminance characteristics of the transistor 6 are shown in FIG. 13. In FIG. 13, the vertical axis indicates the luminance (cd / m 2 ), the horizontal axis is the current FIG. 14 shows the voltage-current characteristics of the light-emitting elements 4 to 6. In the graph, the vertical axis indicates current (mA) and the horizontal axis indicates voltage (V). The chromaticity characteristics are shown in Fig. 15. In Fig. 15, the vertical axis is chromaticity and the horizontal axis is luminance (cd / m 2 ) is shown.

[0210] FIG. 16 shows current efficiency vs. luminance characteristics of the light-emitting elements 4 to 6. In FIG. 16, the vertical axis indicates current Efficiency (cd / A), horizontal axis is brightness (cd / m 2 The power of the light-emitting elements 4 to 6 is shown. The power efficiency-luminance characteristics are shown in Fig. 17. In Fig. 17, the vertical axis represents power efficiency (lm / W) and the horizontal axis represents luminance. Degree (cd / m 2 18 shows the external quantum efficiency vs. luminance characteristics of the light-emitting elements 4 to 6. In Fig. 18, the vertical axis shows the external quantum efficiency (%) and the horizontal axis shows the luminance (cd / m 2 ) is shown. FIG. 19 shows the emission spectra of the light-emitting elements 4 to 6. In FIG. 19, the vertical axis represents the emission intensity ( The horizontal axis indicates wavelength (nm).

[0211] 12 to 19, LE4 represents the light-emitting element 4, LE5 ​​represents the light-emitting element 5, and LE 6 denotes a light emitting element 6.

[0212] 12 to 19, the light-emitting element 4, which has a lower concentration of guest, exhibits a higher optical transmittance than the light-emitting elements 5 and 6. It can be seen that the luminous efficiency is high. Table 5 shows the main characteristics of the light-emitting elements 4 to 6. In Table 5, LE4 represents Light-emitting element 4, LE5 ​​represents Light-emitting element 5, and LE6 represents Light-emitting element 6. As can be seen from Table 5, the luminescence Even though the element 4 is a light-emitting element, it has better properties than the light-emitting elements 5 and 6, which have a higher weight ratio of the guest. It was found that it can be obtained.

[0213] [Table 5] EXAMPLES

[0214] In this embodiment, a phosphorescent compound, an organometallic complex, (acetylacetonato)bis(2-fluorophenyl)phenyl, Phenyldibenzo[f,h]quinoxalinato)iridium(III) (abbreviation: [Ir(db In a light-emitting device using ZnO(acac) as a guest, the concentration of the guest was increased. The structure of [Ir(dbq-P)2(acac)] is shown below.

[0215] [ka]

[0216] The first organic compound used in this example is 2mDBTPDBq-II. The second organic compound used in this example is NPB. The combination of 2mDBTPDBq-II and NPB was the same as in Example 1 (the combination of 2mDBTPDBq-II and PCBNBB). As in the case of Example 1, an exciplex was formed, and the position of the emission spectrum was roughly the same as in Example 1. do.

[0217] In this example, light-emitting elements 7, 8, and 9 were fabricated, each of which has a different concentration of guest. The structures of the light-emitting elements 7, 8, and 9 are shown in FIG. This shows that.

[0218] First, a silicon-containing insulator film having a thickness of 110 nm was prepared as the first electrode 101 functioning as an anode. A glass substrate with an indium tin oxide (ITSO) film was prepared. The ITSO surface was 2 μm thick. The periphery is covered with a polyimide film so that the surface is exposed, and the electrode area is 2 mm × 2 m. As a pretreatment for forming a light-emitting element on this substrate, the substrate surface was washed with water. After baking at 200°C for 1 hour, UV ozone treatment was performed for 370 seconds.

[0219] Then, 10 -4 In the heating chamber of a vacuum deposition device with the inside pressure reduced to about Pa, After 30 minutes of vacuum baking at 400 K, the substrate was left to cool for about 30 minutes. The substrate was fixed to a holder installed in the deposition chamber of the vacuum deposition apparatus so that the coated surface was facing downward. did.

[0220] The deposition chamber was -4 After reducing the pressure to 10 Pa, DBT3P-II and molybdenum(VI) oxide were DBT3P-II:molybdenum oxide = 4:2 (weight ratio) Thus, a hole injection layer 111 was formed. The film thickness was set to 40 nm.

[0221] Subsequently, BPAFLP was evaporated to a thickness of 20 nm to form a hole transport layer 112 .

[0222] Further, on the hole transport layer 112, 2mDBTPDBq-II, NPB, and [Ir(dbq -P)2(acac)], 2mDBTPDBq-II:NPB:[Ir(dbq-P) 2(acac)] = 0.8:0.2:x (weight ratio) The light-emitting layer 113 was formed by the above procedure. Here, x=0.01 in the light-emitting element 7 and x=0.01 in the light-emitting element 8. For the light-emitting element 1, x was set to 0.025, and for the light-emitting element 9, x was set to 0.05.

[0223] Next, 10 nm of 2mDBTPDBq-II was evaporated, followed by 20 nm of BPhen. The electron transport layer 114 was formed by the above-mentioned method. Further, lithium fluoride was deposited on the electron transport layer 114 by 1000 nm. The electron injection layer 115 was formed by vapor deposition so that the thickness of the EL layer 10 was 1 nm. 2 was formed. In the above-mentioned deposition processes, the deposition was all performed using a resistance heating method.

[0224] Finally, an aluminum film is formed to a thickness of 200 nm as the second electrode 103 that functions as a cathode. The light-emitting element was completed. The layer structure of the light-emitting element is shown in Table 6. In the table, x represents the number of layers of the light-emitting element. For light emitting element 7, it is 0.01, for light emitting element 8, it is 0.025, and for light emitting element 9, it is 0.05.

[0225] [Table 6]

[0226] The light-emitting elements (light-emitting elements 7 to 9) obtained in the above manner were placed in a globe in a nitrogen atmosphere. The process of sealing the light-emitting element in the box so that it is not exposed to the atmosphere (the temperature is kept at 80°C during sealing). After performing a heat treatment for 1 hour at 400 K for 1 hour, the operating characteristics of these light-emitting devices were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0227] FIG. 20 shows current density-luminance characteristics of the light-emitting elements 7 to 9. In FIG. 20, the vertical axis indicates luminance (cd / m 2 ), the horizontal axis is the current density (mA / cm 2 In addition, light-emitting elements 7 to The voltage-luminance characteristics of the transistor 9 are shown in FIG. 21. In FIG. 21, the vertical axis indicates the luminance (cd / m 2 ), the horizontal axis is the current FIG. 22 shows the voltage-current characteristics of the light-emitting elements 7 to 9. In the graph, the vertical axis indicates current (mA) and the horizontal axis indicates voltage (V). The chromaticity characteristics are shown in Fig. 23. In Fig. 23, the vertical axis is chromaticity and the horizontal axis is luminance (cd / m 2 ) is shown.

[0228] FIG. 24 shows current efficiency vs. luminance characteristics of the light-emitting elements 7 to 9. In FIG. 24, the vertical axis indicates current Efficiency (cd / A), horizontal axis is brightness (cd / m 2 The power of the light-emitting elements 7 to 9 is shown. The power efficiency-luminance characteristics are shown in Fig. 25. In Fig. 25, the vertical axis represents power efficiency (lm / W) and the horizontal axis represents luminance. Degree (cd / m 2 26 shows the external quantum efficiency vs. luminance characteristics of the light-emitting elements 7 to 9. In Fig. 26, the vertical axis shows external quantum efficiency (%) and the horizontal axis shows luminance (cd / m 2 ) is shown. FIG. 27 shows the external energy efficiency vs. luminance characteristics of the light-emitting elements 7 to 9. In FIG. is the external energy efficiency (%), and the horizontal axis is the brightness (cd / m 2) are shown. The emission spectrum of the molecule 9 is shown in FIG. 28. In FIG. 28, the vertical axis represents the emission intensity (arbitrary unit) and the horizontal axis represents the Wavelengths (nm) are indicated.

[0229] 20 to 28, LE7 denotes the light-emitting element 7, LE8 denotes the light-emitting element 8, and LE 9 denotes a light-emitting element 9.

[0230] 20 to 28, the light-emitting element 7, which has a lower concentration of guest, exhibits a higher optical transmittance than the light-emitting elements 8 and 9. It can be seen that the luminous efficiency is high. Table 7 shows the main characteristics of the light-emitting elements 7 to 9. In Table 7, LE7 represents light-emitting element 7, LE8 represents light-emitting element 8, and LE9 represents light-emitting element 9. As can be seen from Table 7, the luminescence Even though element 7 is a light-emitting element, it has better properties than light-emitting elements 8 and 9, which have a higher weight ratio of the guest. It was found that it can be obtained.

[0231] [Table 7] [Explanation of symbols]

[0232] 101 First electrode 102 EL layer 103 Second electrode 104 First EL layer 105 Second EL layer 106 Charge generation layer 111 Hole injection layer 112 Hole transport layer 113 Light-emitting layer 114 Electron transport layer 115 Electron injection layer 116 Electron injection buffer layer 117 Electronic Relay Layer 118 Composite layer

Claims

1. A light-emitting layer is provided between a pair of electrodes, the light-emitting layer includes a phosphorescent compound, a first organic compound, and a second organic compound; the first organic compound and the second organic compound are a combination that forms an exciplex, a peak of the emission spectrum of the exciplex is closer to an absorption band located on the longest wavelength side of the absorption spectrum of the phosphorescent compound than a peak of the emission spectrum of the first organic compound and a peak of the emission spectrum of the second organic compound; a peak of the emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the phosphorescent compound, a triplet excitation energy level of the first organic compound and a triplet excitation energy level of the second organic compound are higher than a triplet excitation energy level of the phosphorescent compound; A light-emitting element (excluding a combination in which the phosphorescent compound is Ir(DPPF) 3 , the first organic compound is PVK, and the second organic compound is PBD). 【Chemistry 1】

2. A light-emitting layer is provided between a pair of electrodes, the light-emitting layer includes a phosphorescent compound, a first organic compound, and a second organic compound; the first organic compound and the second organic compound are a combination that forms an exciplex, a peak of the emission spectrum of the exciplex is closer to a peak of an absorption band located on the longest wavelength side of an absorption spectrum of the phosphorescent compound than a peak of the emission spectrum of the first organic compound and a peak of the emission spectrum of the second organic compound; a peak of the emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the phosphorescent compound, a triplet excitation energy level of the first organic compound and a triplet excitation energy level of the second organic compound are higher than a triplet excitation energy level of the phosphorescent compound; A light-emitting element (excluding a combination in which the phosphorescent compound is Ir(DPPF) 3 , the first organic compound is PVK, and the second organic compound is PBD). 【Chemistry 2】

3. In claim 1 or 2, The light-emitting element, wherein the first organic compound and the second organic compound are low molecular weight compounds.

4. A light-emitting layer is provided between a pair of electrodes, the light-emitting layer includes a phosphorescent compound, a first organic compound, and a second organic compound; the first organic compound and the second organic compound are low molecular weight compounds; the first organic compound and the second organic compound are a combination that forms an exciplex, a peak of the emission spectrum of the exciplex is closer to an absorption band located on the longest wavelength side of the absorption spectrum of the phosphorescent compound than a peak of the emission spectrum of the first organic compound and a peak of the emission spectrum of the second organic compound; a peak of the emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the phosphorescent compound, A light-emitting element, wherein a triplet excitation energy level of the first organic compound and a triplet excitation energy level of the second organic compound are higher than a triplet excitation energy level of the phosphorescent compound.

5. A light-emitting layer is provided between a pair of electrodes, the light-emitting layer includes a phosphorescent compound, a first organic compound, and a second organic compound; the first organic compound and the second organic compound are low molecular weight compounds; the first organic compound and the second organic compound are a combination that forms an exciplex, a peak of the emission spectrum of the exciplex is closer to a peak of an absorption band located on the longest wavelength side of an absorption spectrum of the phosphorescent compound than a peak of the emission spectrum of the first organic compound and a peak of the emission spectrum of the second organic compound; a peak of the emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of an absorption spectrum of the phosphorescent compound, A light-emitting element, wherein a triplet excitation energy level of the first organic compound and a triplet excitation energy level of the second organic compound are higher than a triplet excitation energy level of the phosphorescent compound.

6. In any one of claims 1 to 5, A light-emitting element, wherein a ratio of a weight of the phosphorescent compound to a sum of a weight of the first organic compound and a weight of the second organic compound is 0.1% or more and 2.5% or less.

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