Light-emitting element

Abstract

To provide a light-emitting element with high external quantum efficiency. [Solution] A light-emitting element having a light-emitting layer containing a guest, an n-type host, and a p-type host between a pair of electrodes, wherein the value obtained by subtracting the energy difference between the triplet excited state and the ground state of the guest from the energy difference between the triplet excited state and the ground state of the n-type host (or p-type host) is 0.15 electron volts or more. In this light-emitting element, transitions from the guest in the triplet excited state to the triplet excited state of the n-type host (or p-type host) are unlikely to occur, so light emission from the guest in the triplet excited state is efficiently performed. Alternatively, a light-emitting element in which the LUMO level of the n-type host is 0.1 electron volts or more higher than the LUMO level of the guest, or the HOMO level of the p-type host is 0.1 electron volts or more lower than the HOMO level of the guest. In this light-emitting element, electron-hole recombination occurs efficiently within the guest, and the luminescence efficiency or external quantum efficiency can be increased.

Description

Technical Field

[0001] Relates to a light-emitting device using an organic electroluminescence (EL) phenomenon (hereinafter also referred to as an organic EL device).

Background Art

[0002] Research and development of organic EL devices are being actively conducted (see Patent Document 1, Non-Patent Document 1, and Non Patent Document 2). The basic structure of an organic EL device is a structure in which a layer containing a light-emitting organic compound (hereinafter also referred to as a light-emitting layer) is sandwiched between a pair of electrodes. Due to characteristics such as being able to be made thin and lightweight, being able to respond quickly to an input signal, and being capable of driving with a low DC voltage, it is attracting attention as a next-generation flat panel display device. In addition, a display using such a light-emitting device also has characteristics of excellent contrast and image quality and a wide viewing angle. Furthermore, since an organic EL device is a surface light source, it is also considered for applications such as a backlight of a liquid crystal display or a light source for lighting.

[0003] The light-emitting mechanism of an organic EL device is a carrier injection type. That is, by applying a voltage across the electrodes with a light-emitting layer sandwiched therebetween, electrons and holes injected from the electrodes recombine, causing the light-emitting substance to become excited, and light is emitted when the excited state returns to the ground state. The excited state includes a singlet excited state and a triplet excited state. Also, the statistical generation ratio in the light-emitting device is considered to be one-third of the former with respect to the latter. In this specification, the singlet excited state (triplet excited state) refers to, unless otherwise specified, the one with the lowest energy level among the singlet excited state (triplet excited state).

[0004] Luminescent organic compounds usually have a singlet ground state. Therefore, luminescence from the singlet excited state is called fluorescence because it is an electronic transition between states of the same spin multiplicity. On the other hand, luminescence from the triplet excited state is called phosphorescence because it is an electronic transition between states of different spin multiplicities. Here, a compound that emits fluorescence (hereinafter referred to as a fluorescent compound) usually exhibits only fluorescence and no phosphorescence at room temperature. Therefore, the theoretical limit of the internal quantum efficiency (the ratio of photons generated to the injected carriers) in a light-emitting device using a fluorescent compound is 25% based on the ratio of the singlet excited state and the triplet excited state described above.

[0005] On the other hand, if a compound that emits phosphorescence (hereinafter referred to as a phosphorescent compound) is used, the internal quantum efficiency can theoretically be increased to 1 00%. That is, higher emission efficiency can be obtained compared to a fluorescent compound. For this reason, in order to realize a highly efficient light-emitting device, the development of light-emitting devices using phosphorescent compounds has been actively carried out in recent years.

[0006] In particular, due to the high phosphorescence quantum efficiency, organometallic complexes having iridium or the like as a central metal have attracted attention as phosphorescent compounds. For example, Patent Document 1 discloses an organometallic complex having iridium as a central metal as a phosphorescent material.

[0007] When forming a light-emitting layer of a light-emitting device using the above-described phosphorescent compound, in order to suppress concentration quenching of the phosphorescent compound and quenching due to triplet-triplet annihilation, the phosphorescent compound is often formed so as to be dispersed in a matrix composed of other compounds. At this time, the compound serving as the matrix is called a host, and the compound dispersed in the matrix like the phosphorescent compound is called a guest. ​ It can be done.

[0008] The general elementary processes of light emission in light-emitting devices that use phosphorescent compounds as guests. There are several, which will be explained below.

[0009] (1) When electrons and holes recombine in the guest molecule and the guest molecule enters an excited state ( direct recombination process). (1-1) When the excited state of the guest molecule is a triplet excited state, the guest molecule emits phosphorescence. (1-2) When the excited state of the guest molecule is a singlet excited state, the guest molecule in the singlet excited state is Intersystem crossing occurs in the triplet excited state, causing phosphorescence.

[0010] In other words, in the direct recombination process described in (1) above, the intersystem crossing efficiency of the guest molecule and phosphorescence If the quantum efficiency is high enough, a high luminescence efficiency can be obtained.

[0011] (2) When electrons and holes recombine in the host molecule and the host molecule enters an excited state ( Energy transfer process.

[0012] (2-1) When the excited state of the host molecule is a triplet excited state, the triplet excited state of the host molecule If the energy level (T1 level) of the host molecule is higher than the T1 level of the guest molecule, then the host molecule Excitation energy is transferred to the guest molecule, causing it to enter a triplet excited state. The guest molecule in this state emits phosphorescence. Note that the energy of the guest molecule in its singlet excited state is... Energy transfer to the S1 level is also formally possible, but in most cases, it is the S of the guest molecule. The 1st energy level is located at a higher energy level than the T1 level of the host molecule, and the main energy Since this process is unlikely to involve ghee migration, we will omit it here.

[0013] (2-2) When the excited state of the host molecule is a singlet excited state, the singlet excited state of the host molecule If the energy level of (S1 level) is higher than the S1 and T1 levels of the guest molecule, Excitation energy is transferred from the host molecule to the guest molecule, and the guest molecule enters a singlet excited state or It enters a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. The guest molecule, once in a no-term excited state, undergoes inter-system crossing to a triplet excited state and emits phosphorescence.

[0014] In other words, in the energy transfer process described in (2) above, the triplet excitation energy of the host molecule The key is how efficiently both the singlet excitation energy and the singlet excitation energy can be transferred to the guest molecule. This is the result.

[0015] Considering this energy transfer process, excitation energy is transferred from the host molecule to the guest molecule. Before that happens, the host molecule itself deactivates by releasing its excitation energy as light or heat. This will result in a decrease in luminous efficiency.

[0016] <Energy transfer process> The following sections will detail the energy transfer processes between molecules.

[0017] First, the following two mechanisms have been proposed for the energy transfer between molecules. So, the molecule that provides the excitation energy is the host molecule, and the molecule that receives the excitation energy is the host molecule. This is referred to as the guest molecule.

[0018] ≪Förster mechanism (dipole-dipole interaction)≫ The Förster mechanism does not require direct contact between molecules for energy transfer. Energy transfer occurs through the resonance phenomenon of dipole vibrations between the child and guest molecules. Through dynamic resonance, the host molecule transfers energy to the guest molecule, and the host molecule then... The system enters a bottom state, and the guest molecule enters an excited state. The rate constant k of the Förster mechanism. h * →g of This is shown in formula (1).

[0019]

number

[0020] In equation (1), ν represents the frequency, and f' h (ν) is the normalized host molecule Emission spectrum (When discussing energy transfer from singlet excited states, use fluorescence spectrum) When discussing energy transfer from a triplet excited state, the phosphorescent spectrum is represented, and ε g (ν ) represents the molar extinction coefficient of the guest molecule, N represents Avogadro's number, and n is the refraction of the medium. R represents the rate, R represents the intermolecular distance between the host molecule and the guest molecule, and τ represents the experimentally measured excitation state. This represents the lifetime of the state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, and φ represents the emission quantum efficiency (single-particle emission). When discussing energy transfer from triplet excited states, fluorescence quantum efficiency and energy transfer from triplet excited states are used. When discussing energy transfer, it represents phosphorescent quantum efficiency, and K 2 This involves the host molecule and the guest molecule. This is a coefficient (0-4) that represents the orientation of the transition dipole moment. Note that in the case of random orientation... K 2 = 2 / 3

[0021] Dexter mechanism (electron exchange interaction) The Dexter mechanism occurs when a host molecule and a guest molecule approach the effective contact distance where their orbitals overlap. Energy is released through the exchange of electrons between the excited host molecule and the ground-state guest molecule. - Movement occurs. The rate constant k of the Dexter mechanism h * →g is shown in Equation (2).

[0022]

Equation

[0023] In Equation (2), h is the Planck constant, K is a constant with the dimension of energy and ν represents the frequency, and f’ h (ν) is the normalized emission spectrum of the host molecule (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state ), ε’ g (ν) represents the normalized absorption spectrum of the guest molecule, L represents the effective molecular radius, and R represents the intermolecular distance between the host molecule and the guest molecule.

[0024] Here, the energy transfer efficiency Φ ET from the host molecule to the guest molecule is considered to be expressed by Equation (3). k is the rate constant of the emission process of the host molecule (fluorescence when discussing energy transfer from the singlet excited state of the host molecule, phosphorescence when discussing energy transfer from the triplet excited state r of the host molecule), k is the rate constant of the non-emission process (thermal deactivation or intersystem crossing), and τ represents the measured lifetime of the excited state of the host molecule. k n is the rate constant of the non-emission process (thermal deactivation or intersystem crossing), and τ represents the measured lifetime of the excited state of the host molecule. τ represents the measured lifetime of the excited state of the host molecule.

[0025] [[ID=--]] [[ID=--]]

Equation

[0026] <000--235>First, from Equation (3), the energy transfer efficiency Φ ETIn order to increase energy transfer The velocity constant k h * →g other competing rate constants k r +k n (=1 / τ) is by far It becomes clear that increasing it is beneficial. And the rate constant k of that energy transfer... h * →g Large To understand this, we can use equations (1) and (2) to determine the Förster mechanism and the Dexter mechanism. In either mechanism, the emission spectrum of the host molecule (energy from the singlet excited state) When discussing Ghee transfer, we discuss fluorescence spectra and energy transfer from triplet excited states. In this case, the phosphorescence spectrum and the absorption spectrum of the guest molecule (usually, since it is phosphorescence, triple) It can be seen that a larger overlap (energy difference between the excited state and the ground state) is desirable.

[0027] For example, the energy difference between the triplet excited state and the ground state of the host molecule is the same as the triplet excited state of the guest molecule. The material is selected so as to overlap with the energy difference between the excited state and the ground state, making it more effective. A rate of energy transfer occurs from the host to the guest.

[0028] However, the above energy transfer occurs from the triplet excited state guest molecule to the ground state The same process occurs in the host molecule. And the triplet excited state and ground state of the host molecule The energy difference should coincide with the energy difference between the triplet excited state and the ground state of the guest molecule. In the selected material, the triplet excited state of the guest molecule energizes the triplet excited state of the host molecule. This also means that energy transfer is easier. As a result, the luminescence efficiency decreases.

[0029] To address such problems, for example, as described in Non-Patent Document 1, host molecules The energy difference between the triplet excited state and the ground state of the guest molecule It has been proposed that this can be overcome by making the energy difference greater than the energy difference between the two.

[0030] Non-patent document 1 describes the energy difference between the triplet excited state and the ground state of the host molecule as the guest molecule The energy difference between the triplet excited state and the ground state of the host molecule is 0.3 electron volts (current (Currently corrected to 0.15 electron volts) By increasing the voltage, the three guest molecules This prevents the transition from the multiplet excited state to the triplet excited state of the host molecule.

[0031] In other words, the energy difference between the triplet excited state and the ground state of the host molecule is the energy difference of the guest molecule. The energy difference between the triplet excited state and the ground state of the molecule is 0.15 electron volts or more. Then, the transition from the triplet excited state of the guest molecule to the triplet excited state of the host molecule is sufficiently It can be stopped. [Prior art documents] [Patent Documents]

[0032] [Patent Document 1] International Publication No. 2000 / 070655 Pamphlet [Non-patent literature]

[0033] [Non-Patent Document 1] Shizuo Tokito et al., ``Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices'', Appl. Phys. Lett., 83, 569 (2003). [Non-Patent Document 2] Vi-En Choong et al., ``Organic light-emitting diodes with a bipolar transport layer'', Appl. Phys. Lett., 75, 172 (1999). [Overview of the project] [Problems that the invention aims to solve]

[0034] However, this means that the energy difference between the host molecule and the guest molecule is different. This means that the above-mentioned Förster mechanism and Dexter mechanism are less likely to occur. The resulting decrease in luminous efficiency is a problem. One aspect of the present invention overcomes this contradiction. This provides a light-emitting element based on a new principle.

[0035] Furthermore, as mentioned above, various excitation processes exist, but excitation processes that cause less deactivation are directly This is a recombination process, and improving its ratio leads to an improvement in luminescence efficiency or external quantum efficiency. This is very preferable. One aspect of the present invention relates to a method for efficiently generating a direct recombination process. The objective is to provide a light-emitting element with high external quantum efficiency. The task is to accomplish this. [Means for solving the problem]

[0036] One aspect of the present invention comprises a phosphorescent compound (guest), a first organic compound, and a second organic compound. The device has a light-emitting layer containing a first organic compound and a second organic compound between a pair of electrodes, and triplet excitation of the first organic compound and the second organic compound. The energy difference between the startup state and the ground state is the energy difference between the guest triplet excited state and the ground state. This light-emitting element is characterized by having a voltage at least 0.15 electron volts greater than the specified value.

[0037] In the above, the first organic compound and the second organic compound form an excited complex in combination. It may also be combined. Furthermore, the first organic compound has better electron transport properties than hole transport properties. Furthermore, the second organic compound may have better hole transport properties than electron transport properties. If color is present, the first organic compound and the second organic compound are, respectively, an n-type host and a p This is called a type host.

[0038] Furthermore, in one aspect of the present invention, a light-emitting layer including a guest, an n-type host, and a p-type host is placed between a pair of electrodes. It has an n-type host LUMO (Lowest Unoccupied Molecules) The ar Orbital level is 0.1 electron volts or more higher than the guest LUMO level. This is a light-emitting element characterized by the following:

[0039] Furthermore, if the guest's LUMO level is too low compared to the n-type host's LUMO level, the electrical conductivity characteristics will be affected. The above is undesirable. Therefore, the LUMO level En of the n-type host is used to determine the LUMO level of the guest. The value obtained by subtracting Ea, (En-Ea), is between 0.1 electron volts and 0.5 electron volts. It is preferable to do so.

[0040] Furthermore, in one aspect of the present invention, a light-emitting layer including a guest, an n-type host, and a p-type host is provided as a pair of electric It is located between poles, and the HOMO (Highest Occupied Molecular Weight) of a p-type host The (lar Orbital) level is more than 0.1 electron volts lower than the guest HOMO level. This is a light-emitting element characterized by the following features.

[0041] Furthermore, if the guest's HOMO level is too high compared to the p-type host's HOMO level, the electrical conductivity characteristics will be affected. The above is undesirable. Therefore, the HOMO level Ep of the p-type host is used to determine the HOMO level of the guest. The value obtained by subtracting Eb, (Ep-Eb), is between -0.5 electron volts and -0.1 electron volts. It is preferable that this be the case.

[0042] In the above-mentioned light-emitting element, the guest is preferably an organometallic complex. In this configuration, at least one of the n-type host and the p-type host may be a fluorescent compound. A light-emitting element according to one aspect of the present invention can be applied to light-emitting devices, electronic devices, and lighting devices. ru.

[0043] In one aspect of the present invention, the light-emitting layer has an n-type host molecule, a p-type host molecule, and a guest molecule. Of course, molecules do not need to be arranged in a regular pattern; they can be in a state with very little regularity. This is acceptable. In particular, when the light-emitting layer is a thin film of 50 nm or less, it will be in an amorphous state. It is preferable to do so, and for that reason, it is preferable to select a combination of materials that do not easily crystallize. stomach.

[0044] Furthermore, in one aspect of the present invention, as shown in Figure 1(A), a first electrode 103 is placed on the substrate 101. Alternatively, a light-emitting element may be provided by stacking the light-emitting layer 102 and the second electrode 104 having the above configuration. Here, the first electrode 103 is either the anode or the cathode, and the second electrode 104 is either the anode or the cathode. It is the other side of the pole.

[0045] Furthermore, one aspect of the present invention is shown in Figure 1(B), where the first electrode 103 and the light-emitting layer 102 In addition to the second electrode 104, there is an injection layer 105 for the first carrier and a transport layer for the first carrier. 106, a second carrier injection layer 107, and a second carrier transport layer 108 were arranged in layers. A light-emitting element may also be used. Here, the first carrier is either an electron or a hole, and the second carrier A is the other half of an electron and a hole. Also, if the first electrode is the anode, the first carrier is a hole. Yes, if the first electrode is the cathode, then the first carrier is an electron. [Effects of the Invention]

[0046] In one aspect of the present invention, the triplet excited state of a host molecule (n-type host and p-type host) and the base The energy difference from the ground state is calculated using the energy difference between the triplet excited state and the ground state of the guest molecule. By increasing the voltage by 0.15 electron volts or more, the triplet excited state of the guest molecule is moved away from the host (n This allows for sufficient prevention of transitions of (type-type host and p-type host) molecules to the triplet excited state. This makes it possible to provide a light-emitting element with high external quantum efficiency.

[0047] On the other hand, regarding energy transfer processes that use the Förster mechanism and the Dexter mechanism The process of energy transfer from an excited complex of an n-type host molecule and a p-type host molecule to a guest molecule. This can be achieved. The excited complex, once energy has been transferred to the guest molecule, becomes an n-type phosphorus. It splits into an N-type host molecule and a p-type host molecule, and the n-type host molecule (or p-type host molecule) triplet The energy difference between the excited state and the ground state is the energy difference between the triplet excited state and the ground state of the guest molecule. Since it is more than 0.15 electron volts higher than the energy difference, the triplet excited state of the guest molecule is n-type hot. Energy transfer does not occur to the triplet excited state of the host molecule (or p-type host molecule). .

[0048] Furthermore, in one aspect of the present invention, for example, the LUMO level of the n-type host molecule is the LU of the guest molecule. The electrons that have conducted through the n-type host molecule are at least 0.1 electron volts higher than the MO level. It preferentially enters the LUMO level of the guest molecule. As a result, the guest molecule becomes an anion. This attracts holes, and the holes and electrons recombine in the guest molecule.

[0049] Furthermore, in one aspect of the present invention, for example, the HOMO level of a p-type host molecule is the HO of a guest molecule. The holes that conduct through the p-type host molecule are located at a level 0.1 electron volts or more lower than the MO level. It preferentially enters the HOMO level of the guest molecule. As a result, the guest molecule becomes a cation. This attracts electrons, and holes and electrons recombine in the guest molecule.

[0050] In this way, by using one aspect of the present invention, a carrier can be efficiently supplied to the guest molecule. In particular, in one aspect of the present invention, light emission Because the layer uses a mixture of n-type and p-type hosts, electrons conduct through the n-type host molecules. Holes tend to conduct through p-type host molecules. As a result, at the LUMO level of the guest molecule... In this case, electrons are injected from the n-type host molecule, and the HOMO level of the guest molecule is supplied by the p-type host. Holes are injected from the molecule. [Brief explanation of the drawing]

[0051] [Figure 1] A figure illustrating various aspects of the present invention. [Figure 2] A diagram illustrating the principle of one aspect of the present invention. [Figure 3]A diagram illustrating the principle of one aspect of the present invention. [Figure 4] A figure showing the current density-luminance characteristics of the light-emitting element of Example 1. [Figure 5] A diagram showing the voltage-luminance characteristics of the light-emitting element of Example 1. [Figure 6] A figure showing the brightness-current efficiency characteristics of the light-emitting element of Example 1. [Figure 7] A figure showing the luminance-external quantum efficiency characteristics of the light-emitting element of Example 1. [Figure 8] A figure showing the emission spectrum of the light-emitting element of Example 1. [Figure 9] This figure shows the results of the reliability test of the light-emitting element of Example 1. [Figure 10] This figure shows the current density-luminance characteristics of the light-emitting element of Example 2. [Figure 11] A figure showing the voltage-luminance characteristics of the light-emitting element of Example 2. [Figure 12] This figure shows the brightness-current efficiency characteristics of the light-emitting element of Example 2. [Figure 13] This figure shows the luminance-external quantum efficiency characteristics of the light-emitting element of Example 2. [Figure 14] A figure showing the emission spectrum of the light-emitting element of Example 2. [Figure 15] This figure shows the results of the reliability test of the light-emitting element in Example 2. [Modes for carrying out the invention]

[0052] Embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description. Without departing from the spirit and scope of the present invention, its form and details may be modified in various ways. It will be easily understood by those skilled in the art to obtain this. Therefore, the present invention is as shown in the embodiments below. The description is not to be interpreted as being limited to the stated content. The same reference numeral is used in common across different drawings for parts that are identical or have similar functions. I will omit the explanation of that repetition.

[0053] (Embodiment 1) In this embodiment, the principle of the light-emitting element of one aspect of the present invention will be described with reference to FIG. 2. FIG 2(A) shows the energy states of these molecules when two n-type host molecules (H_n_1, H_n_2), one guest molecule (G) and two p-type host molecules (H_p_1, H_p_2) are arranged linearly Each molecule has its own HOMO and LUMO

[0054] Here, for simplicity of explanation, the LUMO level En of the n-type host molecule and the L UMO level Ea of the guest molecule are made equal, and the HOMO level Ep of the p-type host molecule and the HO MO level Eb of the guest molecule are made equal, but this is not limited to such a case, -0.3 [electron volts] <Ea - En < +0.3 [electron volts], -0.3 [electron volts]) < Eb - Ep < +0 .3 [electron volts] is sufficient. Also, the difference between the LUMO level and the HOMO level of the n-type host molecule (or p-type host molecule) is preferably 0 .5 electron volts or more greater than the difference between the LUMO level and the HOMO level of the guest molecule .

[0055] In the ground state, all of the n-type host molecule, p-type host molecule, and guest molecule have two electrons in the HOMO and no electrons in the LUMO. For example, the n-type host molecule H_n_2, the guest molecule G, and the p-type host molecule H_p_2 have two electrons in the HOMO and no electrons in the LUMO .

[0056] On the other hand, since holes are injected from the anode (right side of the figure) and electrons are injected from the cathode (left side of the figure), the n-type host molecule H_n_1 has an electron in the LUMO, and the p-type host molecule H_p_1 has an electron in the HOMO It is in a state where there is only one electron (one hole). In other words, n-type host molecule H _n_1 is an anion, and the p-type host molecule H_p_1 is a cation.

[0057] Electrons and holes conduct by hopping between such n-type and p-type host molecules. Then, as shown in Figure 2(B), electrons are placed in the LUMO of the guest molecule, and holes are placed in the HOMO. A molecule is injected (direct recombination process), and the guest molecule enters an excited state (intramolecular exciton, exciton) Yes. Thus, even in the direct excitation-recombination process, especially from n-type and p-type hosts, The phenomenon in which a carrier is directly injected into the tortoise is described as Guest Coupled with Co This is called a plenary host (GCCH).

[0058] By the way, as is clear from Figure 2, the difference between the LUMO level and the HOMO level of the n-type host molecule. The difference between the LUMO and HOMO levels of the p-type host molecule is the LU of the guest molecule. The difference between the MO level and the HOMO level is considerably larger, so the Förster mechanism and the Dexter mechanism This causes the guest's triplet excited state to become the triplet excited state of the n-type or p-type host. The probability of a transition is sufficiently small.

[0059] That is, as shown in Figure 2(C), the base of the guest molecule G and the n-type host molecule H_n_1 When the bottom state (S0_G, S0_H_n_1, respectively) is used as the reference, the n-type host molecule H The energy level T1_H_n_1 of the triplet excited state of _n_1 is the triplet excited state of the guest molecule G. Since the energy level T1_G of the initial state is higher by ΔEt (≧0.15 electron volts), This transition is unlikely to occur at room temperature. Note that in Figure 2(C), S1_G and S1_H_n_1 These represent the singlet excited states of the guest molecule G and the n-type host molecule H_n_1, respectively. It is a level.

[0060] Figure 2(C) describes the energy state of the n-type host molecule, but for the p-type host molecule... However, the energy level of that triplet excited state is the same as the energy of the triplet excited state of the guest molecule. A similar effect can be obtained if the level is higher than the threshold level.

[0061] Strictly speaking, the difference between the LUMO level and the HOMO level of a molecule is the difference between the triplet excited state and the ground state of that molecule. It's not exactly an energy difference with the state, but there is a certain correlation. For example, as will be discussed later (A Cetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviated) The name [Ir(dppm)2(acac)]) is used as a guest, but its HOMO The difference between the level and the LUMO level is 2.58 electron volts, whereas its triplet excited state and the base The energy difference from the bottom state is 2.22 electron volts. Furthermore, it is used as an n-type host. 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoki Sarin (abbreviation: 2mDBTPDBq-II) has an electron volt of 3.10 and 2.5, respectively. 4,4'-di(1-naphthyl)-4' is a 4-electronvolt host used as a p-type host. '-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PC) BNBB is 3.15 electron volts and 2.40 electron volts, respectively.

[0062] By the way, the above [Ir(dppm)2(acac)] is used as the guest, and as an n-type host... 2mDBTPDBq-II, when PCBNBB is used as the p-type host, 2mDBTP Energy difference between the triplet excited state and ground state of DBq-II and the triplet state of PCBNBB The energy difference between the excited state and the ground state (according to optical measurements, these are 2.54 electrons each) (2.40 electron volts) is the energy difference between the triplet excited state and the ground state of the guest. The optical measurement results show that it is more than 0.18 electron volts higher than 2.22 electron volts, so The triplet excited state of the host rarely transfers to the host.

[0063] Also, as a guest, (dipivaloylmethanato)bis(3,5-dimethyl-2-phenylp Radinato Iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]) It can also be used. Triplet excited state and ground state of [Ir(mppr-Me)2(dpm)] The energy difference between the states is 2.24 electron volts, according to optical measurements.

[0064] Therefore, 2mDBTPDBq-II is used as the n-type host and PCBNB as the p-type host. When B is used, the energy difference between those triplet excited states and the ground state is [Ir(mp The energy difference between the triplet excited state and the ground state of pr-Me)2(dpm) is 0.16 Since the voltage is higher than electron volts, the triplet excited state of the guest is unlikely to transfer to the host.

[0065] The above describes a direct recombination process in which electrons and holes are injected into the guest molecule, but it involves an n-type host molecule and p A type host molecule forms an excited complex, and this complex transfers energy to the guest molecule, The guest molecule can also be put into an excited state. In this case, energy transfer is performed by ferrules. It uses a star mechanism or a Dexter mechanism.

[0066] An exciplex is formed by the interaction between different molecules in the excited state. It is generally known that an exciplex is likely to be formed between a material with a relatively deep LUMO level and a material with a shallow HOMO level. For example, a p-type host can be used as the former and an n-type host as the latter. Here, the HOMO and LUMO levels of the n-type host and the p-type host are different from each other, and the HOMO level of the n-type

[0067] host < the HOMO level of the p-type host < the LUMO level of the n-type host < the LUMO level of the p-type host, in this order, is high. When an exciplex is formed by this n-type host and p-type host, the LUMO [[ID=...]] level of the exciplex is derived from the n-type host, and the HOMO level is derived from the p-type host. Therefore, the energy difference of the exciplex is smaller than the energy difference of the n-type host and the energy difference of the p-type host. That is, compared with the emission wavelengths of the n-type host and the p-type host respectively, the emission wavelength of the exciplex becomes longer. The formation process of the exciplex can be roughly divided into the following two processes. <000....]]

[0069] ≪Electroplex≫ In this specification, an electroplex refers to the direct formation of an exciplex from a ground-state n-type host and a ground-state p type host.

[0070] As described above, in the Förster mechanism and the Dexter mechanism, when electrons and holes recombine in the host, excitation energy moves from the excited-state host to the guest, and the guest reaches the excited state and emits light. B

[0071] ​ Here, before excitation energy is transferred from the host to the guest, the host itself emits light, In this case, some of the excitation energy is lost as it is converted into thermal energy. In particular, When Sto is in a singlet excited state, the excitation lifetime is shorter compared to when it is in a triplet excited state. Therefore, singlet exciton deactivation is likely to occur. Exciton deactivation leads to a reduction in the lifespan of the light-emitting element. It is one of the contributing factors.

[0072] On the other hand, in one aspect of the present invention, since the n-type host and the p-type host are present in the same light-emitting layer, Whether the p-type host molecule and the p-type host molecule are in a state with a carrier (anion and cation) Therefore, they often form electroplexes. For this reason, n-type hosts with short excitation lifetimes are often used. Singlet excitons are unlikely to be formed in molecules or p-type host molecules.

[0073] In other words, it is a process that directly forms excited complexes without forming singlet excitons in individual molecules. This is the case for the majority. This also suppresses the deactivation of the singlet excitons mentioned above. Then, energy is transferred from the resulting electroplex to the guest, resulting in high luminescence efficiency. A light-emitting element can be obtained.

[0074] Formation of excited complexes by excitons Another process involves one of the host molecules, either the n-type or p-type host molecule, becoming single-layered. One possible elementary process involves the formation of a term exciton, followed by interaction with the other state in the ground state to form an excited complex. Unlike electroplex, in this case, an n-type host molecule or p Singlet excitons are generated from the host molecule, but if these can be quickly converted into an excited complex... Therefore, it is possible to suppress the deactivation of singlet excitons. Furthermore, as mentioned above, n-type phosphor This process is unlikely to occur when the t and p-type host are present in the same light-emitting layer.

[0075] For example, n-type hosts are electron-trapping compounds, while p-type hosts are hole-trapping compounds. These are compounds of a certain sex. When the difference between the HOMO level and the LUMO level of these compounds is large... When the difference is greater than or equal to 0.3 eV, electrons preferentially enter the n-type host molecule, and holes preferentially enter the n-type host molecule. It first enters the p-type host molecule. In this case, the process involves the formation of an excited complex via singlet excitons. It is thought that the process of electroplex formation takes precedence over other processes.

[0076] By the way, the energy transfer from the excited complex formed as described above to the guest molecule is as follows: This is due to the Förster mechanism and the Dexter mechanism, but as mentioned above, these mechanisms In this case, for example, the energy difference between the triplet excited state and the ground state of the host molecule and the guest molecule It is preferable that the energy difference between the triplet excited state and the ground state is small.

[0077] In this case, the energy difference between the triplet excited state and the ground state of the excited complex is the energy difference of the n-type host molecule. This corresponds to the difference between the LUMO level and the HOMO level of the p-type host molecule, and these represent the LU of the guest molecule. When the difference between the MO level and the HOMO level is equal to or close to that of the HOMO level, energy is transferred efficiently. This allows the guest molecule to be placed in a triplet excited state, while the excited complex itself returns to its ground state.

[0078] However, since the excited complex is only stable in the excited state, when it returns to the ground state, the n-type host component... It separates into the child and the p-type host molecule. Then, as described above, these triplet excited states and the ground state The energy difference between the states is calculated from the energy difference between the triplet excited state and the ground state of the guest molecule. Because of its large size, the triplet excited state of the guest molecule is transferred to one of the host molecules. This is extremely unlikely to happen at room temperature.

[0079] (Embodiment 2) In this embodiment, the principle of a light-emitting element according to one aspect of the present invention will be explained with reference to Figure 3. 3(A) consists of two n-type host molecules (H_n_1, H_n_2) and one guest molecule (G). And these when two p-type host molecules (H_p_1, H_p_2) are arranged in a straight line. This shows the energy distribution of the molecules. Each molecule has both a HOMO and a LUMO.

[0080] Here, the LUMO level En of the n-type host molecule is 0 lower than the LUMO level Ea of the guest molecule. It is more than 1 electron volt higher, and the HOMO level Ep of the p-type host molecule is higher than the HOM of the guest molecule. Assume that the O level is higher than Eb. Also, the difference between the LUMO level and the HOMO level of the n-type host molecule is... The difference between the LUMO and HOMO levels of a p-type host molecule is determined by the LUM of the guest molecule. It is preferable that the difference between the O level and the HOMO level is 0.5 electron volts or more greater.

[0081] As shown in Figure 3(A), holes are released from the anode (right side of the figure) and electrons are released from the cathode (left side of the figure). Because it was introduced, the n-type host molecule H_n_1 also has electrons in the LUMO, and the p-type host molecule H _p_1 is in a state where there is only one electron in the HOMO (there is one hole). In other words, the n-type host molecule H_n_1 is an anion, and the p-type host molecule H_p_1 is a catio. It is.

[0082] Electrons and holes conduct by hopping between such n-type and p-type host molecules. As shown in the figure, the LUMO level of the p-type host molecule is different from the LUMO level of the n-type host molecule. Because the HOMO level of the n-type host molecule is also high, electrons conduct through the n-type host molecule. Since the current level is lower than the HOMO level of the p-type host molecule, holes conduct through the p-type host molecule.

[0083] Then, as shown in Figure 3(B), electrons are injected into the LUMO of the guest molecule, and the guest molecule This becomes an anion. Here, the LUMO level of the n-type host molecule is the LUMO level of the guest molecule. It is more than 0.1 electron volts higher than that, and of course, the LUMO level of the p-type host molecule is even higher. Then, the electrons that enter the LUMO of the guest molecule become metastable, so to speak, the guest The molecules become trapped.

[0084] As a result, the guest molecule becomes a negatively charged anion, and thus attracts the surrounding holes. It is attracted by interaction (indicated as F in the figure). Therefore, as shown in Figure 3(C), Holes in the p-type host molecule H_p_2 are injected into the guest molecule G. Coulomb interaction Because the ray extends relatively far, electrons and holes efficiently accumulate within the guest molecule.

[0085] In this case, the electrons in the LUMO of the guest molecule G and the HOM of the p-type host molecule H_p_2 are considered. It recombines with the hole in O (i.e., the electron in the LUMO of the guest molecule G is p-type host It moves to the HOMO of the molecule H_p_2, or to the HOMO of the p-type host molecule H_p_2. When a hole located in the molecule moves to the LUMO of the guest molecule G, light emission occurs at that point.

[0086] Furthermore, if the above electron transfer is prohibited, there is a hole in the HOMO of the p-type host molecule H_p_2. The HOMO of guest molecule G moves to the HOMO of guest molecule G, and guest molecule G enters an excited state. Subsequently, the guest molecule The G molecule transitions to the ground state, but light emission occurs during this process.

[0087] To induce holes in the guest via Coulomb interaction, (the HOMO level of the p-type host) - (Guest's HOMO level) as ΔEp, (n-type host's LUMO level) - (Guest's LUM When the O level is ΔEn, then ΔEp < ΔEn + 0.2 [electron volts], preferably Δ It is preferable to set Ep < ΔEn. Due to the above action, holes and electrons recombine within the guest molecule. .

[0088] The above process occurs because the guest molecule becomes an anion. If the charge of the guest molecule If neutral, the HOMO level of the guest molecule is lower than the HOMO level of the p-type host molecule. Therefore, the likelihood of holes being injected into the guest molecule is low.

[0089] Figure 3 shows that the LUMO level En of the n-type host molecule is higher than the LUMO level Ea of the guest molecule. Furthermore, if the HOMO level Ep of the p-type host molecule is higher than the HOMO level Eb of the guest molecule... However, conversely, the HOMO level Ep of the p-type host molecule is different from the HOMO level Eb of the guest molecule. It is more than 0.1 electron volts lower, and the LUMO level En of the n-type host molecule is lower than that of the guest molecule. The same principle applies even when the LUMO level is 0.1 electron volts or more lower than Ea within the guest molecule. Holes and electrons recombine efficiently. In this case, holes are initially deposited on the HOMO of the guest molecule. Electrons are introduced, and through Coulomb interaction, electrons are injected into the guest molecule.

[0090] Furthermore, the LUMO level En of the n-type host molecule is higher than the LUMO level Ea of the guest molecule, Furthermore, if the HOMO level Ep of the p-type host molecule is lower than the HOMO level Eb of the guest molecule, Furthermore, it is possible to more efficiently inject charge into the guest and bring it into an excited state. In that case, At the very least, the LUMO level En of the n-type host molecule is 0.1 lower than the LUMO level Ea of the guest molecule. The HOMO level Ep of the p-type host molecule is higher than the HOMO level of the guest molecule. It is preferable that the voltage is at least 0.1 electron volts lower than Eb.

[0091] Furthermore, in adjacent fields, the n-type host molecule that has become an anion and the p-type host molecule that has become a cation In combination, the two molecules may enter an excited complex state. In this case, a nearby guest molecule may enter an excited state. To achieve this, the energy transfer process described above is necessary, but in that case, the excited complex The energy difference between the excited state and the ground state and the energy difference between the triplet excited state and the ground state of the guest molecule The closer the energy difference, the better.

[0092] If the LUMO level of the n-type host molecule is 0.1 electron levels lower than the LUMO level of the guest molecule, If only the HOMO level is high, the HOMO level of the p-type host molecule will be 0 lower than the HOMO level of the guest molecule. By selecting a material that is only 1 electron volt lower, the excitation of the excited state and ground state of the excited complex is reduced. The energy difference and the energy difference between the triplet excited state and the ground state of the guest molecule are made as equal as possible. You should make it so that it doesn't happen.

[0093] Specifically, the LUMO standard of [Ir(dppm)2(acac)] used as a guest The electron level and HOMO level are -2.98 electron volts and -5.56 electron volts, respectively. Furthermore, 2mDBTPDBq-II, which is used as an n-type host, has values ​​of -2.78. The electron volt is -5.88 electron volts, and the PCBNBB used as a p-type host is These are -2.31 electron volts and -5.46 electron volts, respectively.

[0094] In this combination, the guest's LUMO level is the LU of the n-type host and the p-type host. It is lower than the MO level, and especially 0.2 electron volts lower than the LUMO level of an n-type host, therefore The tomolecule easily traps electrons and becomes anion. Also, the HOMO level of the guest molecule is Although it is higher than the HOMO level of the n-type host molecule, it is higher than the HOMO level of the p-type host molecule. It's 0.1 electron volts lower.

[0095] Therefore, as shown in Figure 3, electrons are first injected into the guest LUMO, and then the cooldown is reduced. The guest element emits light when holes are injected into it through the Rhon interaction.

[0096] Furthermore, the LUMO level of [Ir(mppr-Me)2(dpm)] is -2.77 electron volts. It is a type n host (2mDBTPDBq-II) with a LUMO level of -2.78 electrons. It is almost the same as (Lut), and also the HOM of [Ir(mppr-Me)2(dpm)] The O level is -5.50 electron volts, and the HOMO level of a p-type host (PCBNBB) is (- It is 0.07 electron volts lower than 5.43 electron volts.

[0097] These values ​​are [Ir(mppr-Me)2(dpm)] for the above n-type host and p-type host When used with [Ir(dppm)], it has the effect of trapping electrons and holes. This indicates that it is inferior to )2(acac).

[0098] (Embodiment 3) In this embodiment, a light-emitting element according to one aspect of the present invention will be described using Figure 1(B). 1(B) is a light-emitting element having an EL layer 110 between the first electrode 103 and the second electrode 104. This is a diagram showing the child. In Figure 1(B), the light-emitting element is stacked sequentially on the first electrode 103. The first carrier injection layer 105, the first carrier transport layer 106, the light-emitting layer 102, A transport layer 108 for the second carrier, an injection layer 107 for the second carrier, and further provided on top of that It consists of a second electrode 104. The EL layer 110 is composed of the first electrode 104 in addition to the light-emitting layer 102. Carrier injection layer 105, first carrier transport layer 106, second carrier transport layer 10 8. It consists of a second carrier injection layer 107. Note that the EL layer 110 is not necessarily this It is not necessary to have all of these layers.

[0099] Here, the first electrode 103 is either the anode or the cathode, and the second electrode 104 is the anode. The first is the other side of the cathode. Also, the first carrier is either a hole or an electron, and the second The carriers are either holes or electrons. Also, if the first electrode is the anode, then the first The carriers are holes, and if the first electrode is the cathode, then the first carriers are electrons. The first carrier injection layer 105 and the second carrier injection layer 107 are hole injection layers and electron injection layers. It is either the in-layer, the transport layer 106 of the first carrier, or the transport layer 108 of the second carrier. It is either a hole transport layer or an electron transport layer.

[0100] As the anode, metals, alloys, and conductive compounds with a large work function (specifically 4.0 eV or higher) are suitable. It is preferable to use substances and mixtures thereof. Specifically, for example, indioxide Contains um-tin oxide (ITO), silicon, or silicon oxide. Indium oxide-tin oxide, indium oxide-zinc oxide Indium oxide (IWZO) containing tungsten oxide and zinc oxide. These are some examples. These conductive metal oxide films are usually deposited by sputtering. However, it is also acceptable to prepare them using methods such as the sol-gel method.

[0101] For example, an indium oxide-zinc oxide film contains 1-20 wt% zinc oxide relative to indium oxide. It can be formed by sputtering using a target with lead added. The WZO film contains 0.5-5 wt% tungsten oxide and 0 wt% zinc oxide relative to indium oxide. It can be formed by sputtering using a target containing 0.1 to 1 wt% of the substance. In addition, graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, iron Examples include cobalt, copper, palladium, or nitrides of metallic materials (e.g., titanium nitride). It can be done.

[0102] However, of the EL layer 110, the layer formed in contact with the anode is an organic compound and electron receiver, as described later. When formed using a composite material obtained by mixing with an acceptor, the anode is used The materials present include various metals, alloys, electrically conductive compounds, and, regardless of the magnitude of their work function. These mixtures can be used. For example, aluminum, silver, aluminum Other alloys (e.g., Al-Si) can also be used. The anode can be, for example, sputtering. It can be formed by methods such as vacuum deposition or other deposition methods.

[0103] The cathode is a metal, alloy, or electrically conductive compound with a low work function (preferably 3.8 eV or less). It is preferable to form them using, and mixtures thereof. Specifically, of the periodic table of elements Elements belonging to Group 1 or Group 2, namely alkali metals such as lithium and cesium, and Alkaline earth metals such as calcium and strontium, magnesium, and substances containing these. alloys (e.g., Mg-Ag, Al-Li), europium, ytterbium, and other rare earth elements. In addition to metals and alloys containing them, aluminum, silver, and other materials can be used.

[0104] However, of the EL layer 110, the layer formed in contact with the cathode is composed of organic compounds and electrons, as described later. When using a composite material formed by mixing a donor material, regardless of the magnitude of the work function Al, Ag, ITO, silicon, or silicon oxide-containing indium oxide-tin oxide, etc. Various conductive materials can be used. When forming the cathode, vacuum deposition or saturates can be used. The puttering method can be used. Alternatively, when using silver paste, the coating method can be used. Methods such as inkjet printing can be used.

[0105] The hole injection layer is a layer containing a material with high hole injection potential. Examples of materials with high hole injection potential include: Molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide Materials, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide Metal oxides such as tungsten oxide and manganese oxide can be used. Talocyanine (abbreviated as H2Pc), copper(II) phthalocyanine (abbreviated as CuPc), etc. Talocyanine compounds can be used.

[0106] Furthermore, the low molecular weight organic compound 4,4',4''-tris(N,N-diphenylamino ) Triphenylamine (abbreviation: TDATA), 4,4',4''-tris[N-(3-methylamine) [Tylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), 4 ,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphen Lu (abbreviation: 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]benzene (abbreviation: DPA3B), 3-[N-(9-phenylcarbazole-3-yl) )-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3, 6-Bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9- Phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-( 9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole (abbreviation: P Aromatic amine compounds such as CzPCN1 can be used.

[0107] Furthermore, polymer compounds (oligomers, dendrimers, polymers, etc.) can also be used. For example, poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyl truffle) Phenylamine (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenyl [phenylamino]phenyl-N'-phenylamino}phenyl)methacrylamide] (Abbreviation: PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bi Examples of high-molecular-weight compounds include poly(phenyl)benzidine (abbreviated as Poly-TPD). Also, poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS), Polyaniline / Poly(styrene sulfonate) (PAni / PS Polymer compounds to which acids such as S) have been added can be used.

[0108] Furthermore, a hole injection layer is formed by mixing an organic compound with an electron acceptor. Composite materials may be used. Such composite materials have holes in the organic compound due to electron acceptors. Because it generates holes, it exhibits excellent hole injection and hole transport properties. In this case, as an organic compound It is preferable that the material is one that is excellent at transporting the generated holes (a substance with high hole transport properties).

[0109] Organic compounds used in composite materials include aromatic amine compounds, carbazole derivatives, and fragrances. Various compounds such as hydrocarbons and polymers (oligomers, dendrimers, polymers, etc.) Materials can be used. Furthermore, as organic compounds used in composite materials, high hole transport properties are preferred. It is preferable that it be an organic compound. Specifically, 10 -6 cm 2 Hole movement of / Vs or greater It is preferable that the material has a degree of [unclear]. However, it is not necessarily a material that has higher hole transport than electron transport. However, other materials may also be used. Below, we will discuss organic compounds that can be used in composite materials. List the specific ingredients.

[0110] Examples of organic compounds that can be used in composite materials include TDATA and MTDATA. , DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN 1,4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl Nyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4-phenyl -4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFL) Aromatic amine compounds such as P), and 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-antryl)f [enyl]-9H-carbazole (abbreviation: PCzPA), 1,4-bis[4-(N-carbazole) Carbazole derivatives such as zolyl)phenyl]-2,3,5,6-tetraphenylbenzene You can use it.

[0111] Also, 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 , aromatic hydrocarbon compounds such as 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene can be used.

[0112] 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, anth racene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-but yl)perylene, pentacene, coronene, 4,4'-bis(2,‘2-diphenylvinyl) biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl) phenyl]anthracene (abbreviation: DPVPA) and other aromatic hydrocarbon compounds can be used.

[0113] In addition, as the electron acceptor, organic compounds such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, etc., and transition metal oxides can be mentioned. Also, oxides of metals belonging to Groups 4 to 8 in the periodic table of elements can be mentioned. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferred because they have high electron accepting properties. Among them, molybdenum oxide is particularly preferred because it is stable in the atmosphere, has low hygroscopicity, and is easy to handle.

[0114] ​​​​​ Furthermore, the polymer compounds mentioned above, such as PVK, PVTPA, PTPDMA, and Poly-TPD... Furthermore, a composite material may be formed using the electron acceptors described above and used as a hole injection layer.

[0115] A hole transport layer is a layer containing a substance with high hole transport properties. Examples of substances with high hole transport properties include: NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluorene- 2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), 4,4'-bi Su[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]bife Aromatic amine compounds such as nyl (abbreviated as BSPB) can be used. The substance is mainly 10 -6 cm 2 It is a material having a hole mobility of / Vs or greater. However, electrons Other substances may be used as long as they have high hole transport properties. Layers containing highly ferrous materials include not only single layers, but also layers of the above materials stacked in two or more layers. It may be considered as such.

[0116] Furthermore, the hole transport layer contains carbazole derivatives such as CBP, CzPA, and PCzPA, Anthracene derivatives such as t-BuDNA, DNA, and DPAnth may also be used.

[0117] Furthermore, the hole transport layer contains high-quality materials such as PVK, PVTPA, PTPDMA, and Poly-TPD. Molecular compounds can also be used.

[0118] The light-emitting layer 102 is a layer containing a light-emitting material. In this embodiment, the light-emitting layer 102 is a guest layer. It has a phosphorescent compound and has n-type and p-type hosts. n-type host ( Alternatively, two or more types of p-type hosts can be used.

[0119] As the phosphorescent compound, an organometallic complex is preferable, and an iridium complex is particularly preferable. In addition, considering the energy transfer by the above-mentioned Förster mechanism, the molar absorption coefficient of the absorption band located on the longest wavelength side of the phosphorescent compound is 2000 M ·cm -1 ·cm -1 or more is preferable, and 5 000 M -1 ·cm -1 or more is particularly preferable.

[0120] Examples of the compound having such a large molar absorption coefficient include [Ir(mppr-M e)2(dpm)] and [Ir(dppm)2(acac)]. In particular, like [Ir(dppm)2(acac)], when a material with a molar absorption coefficient reaching 5000 M -1 ·cm - 1 or more is used, a light-emitting device with an external quantum efficiency reaching about 30% can be obtained. .

[0121] Examples of the n-type host include, in addition to the above-mentioned 2mDBTPDBq-II, 2-[4-( 3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzof [h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4- yl)phenyl]dibenzof [h]quinoxaline (abbreviation: 7mDBTPDBq-II) , and 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzof [h]quinoxaline (abbreviation: 6mDBTPDBq-II), and any one of the compounds that easily accept electrons can be used. , and 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzof [h]quinoxaline (abbreviation: 6mDBTPDBq-II).

[0122] In addition to the PCBNBB mentioned above, other p-type hosts include 4,4'-bis[N-(1-na Phthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), and 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenyl A compound that readily accepts holes, such as mine (abbreviated as PCBA1BP), can be used. Furthermore, without being limited to these, for example, as shown in Embodiment 1 or Embodiment 2 Any combination of an n-type host and a p-type host that satisfies the relationship between the energy levels is acceptable.

[0123] The electron transport layer is a layer containing a material with high electron transport properties. Examples of materials with high electron transport properties include: Alq3, Tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3) , bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq2), BAlq, Zn(BOX)2, bis[2-(2-hydroxyphenyl)benzothiazolat Examples include metal complexes such as zinc (abbreviated as Zn(BTZ)2).

[0124] Also, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4 -Oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenate) [Nyl]-1,3,4-oxadiazole-2-yl]benzene (abbreviation: OXD-7), 3 -(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1, 2,4-Triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4- (4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation) :p-EtTAZ), vasophenanthroline (abbreviation: BPhen), vasocuproin ( Abbreviation: BCP), 4,4'-bis(5-methylbenzoxazol-2-yl)stilbe Heteroaromatic compounds such as β-(bzOs) can also be used.

[0125] Also, poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexyl) (Abbreviation: PF) -Py), poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2 High molecular weight compounds such as '-bipyridine-6,6'-diyl' (abbreviation: PF-BPy) It can also be used. The substances mentioned here are mainly 10 -6 cm 2 Electron mobility greater than / Vs It is a substance that has [a certain characteristic]. Furthermore, any substance with higher electron transport capabilities than holes is acceptable, other than those mentioned above. The material may be used as an electron transport layer.

[0126] Furthermore, electron transport layers are not limited to single layers, but also consist of two or more layers made of the above material stacked together. It would also be acceptable to do so.

[0127] The electron injection layer is a layer containing a material with high electron injection potential. Examples of electron injection layers include lithium and cesium. Um, calcium, lithium fluoride, cesium fluoride, calcium fluoride, lithium oxide Alkali metals, alkaline earth metals, or compounds thereof can be used. It is possible to use rare earth metal compounds such as erbium fluoride. The materials that make up the electron transport layer described above can also be used.

[0128] Alternatively, a composite material consisting of an organic compound and an electron donor in the electron injection layer. Such composite materials may be used. In such composite materials, electrons are generated in the organic compound by the electron donor. Therefore, it has excellent electron injection and electron transport properties. In this case, as an organic compound, It is preferable that the material is excellent in transporting the generated electrons, specifically, for example, the electrons mentioned above The transport layer can be composed of materials such as metal complexes or heteroaromatic compounds.

[0129] Any substance that exhibits electron-donating properties towards organic compounds can be used as an electron donor. Specifically, Alkali metals, alkaline earth metals, and rare earth metals are preferred, as are lithium, cesium, and magnesium. Examples include nesium, calcium, erbium, and ytterbium. Also, alkali gold Metal oxides and alkaline earth metal oxides are preferred, as are lithium oxides, calcium oxides, and barium oxides. Examples include magnesium oxides. Additionally, using Lewis bases such as magnesium oxide is also an option. It is also possible to use organic compounds such as tetrathiafulvalene (abbreviated as TTF). can.

[0130] Furthermore, the hole injection layer, hole transport layer, light-emitting layer 102, electron transport layer, and electron injection layer described above are These are formed by methods such as vapor deposition (including vacuum deposition), inkjet printing, and coating. It is possible.

[0131] Furthermore, as shown in Figure 1(C), multiple EL layers 110a and 110b are located between the anode and the cathode. They may be stacked. In this case, the EL layers 110a and 110b each emit light at least. It has layers. Between the stacked first EL layer 110a and the second EL layer 110b, It is preferable to provide a charge generation layer 111. The charge generation layer 111 is formed from the composite material described above. This can be done. Also, the charge generation layer 111 is the intersection of a layer made of a composite material and a layer made of other materials. A layered structure is also acceptable.

[0132] In this case, the layer made of other materials includes an electron-donating substance and a substance with high electron-transporting properties. A layer made of a transparent conductive film or the like can be used. The element is less prone to problems such as energy transfer and quenching, and offers a wider range of material choices. This makes it easy to create a light-emitting element that combines high luminous efficiency and a long lifespan. It is also easy to obtain phosphorescence emission in the EL layer and fluorescence emission in the other layer. This structure is the same as the EL layer described above. It can be used in combination with a structure.

[0133] Furthermore, by making the light-emitting color of each EL layer different, the entire light-emitting element can be desired Light emission of the following colors can be obtained. For example, the light emission color of the first EL layer 110a and the second EL layer By making the emission colors of 110b complementary, the entire light-emitting element emits white light. It is also possible to obtain a light-emitting element. Furthermore, in the case of a light-emitting element having three or more EL layers, The same applies to the latter.

[0134] Alternatively, as shown in Figure 1(D), a hole injection layer 20 is placed between the anode 201 and the cathode 209. 2. Hole transport layer 203, light-emitting layer 204, electron transport layer 205, electron injection buffer layer 206 , an EL layer 210 having an electronic relay layer 207 and a composite material layer 208 in contact with the cathode 209 It is also acceptable to form it.

[0135] By providing a composite material layer 208 in contact with the cathode 209, the cathode can be made to work particularly well when using the sputtering method. This is preferable because it reduces the damage the EL layer 210 receives when forming the pole. The composite material layer 208 contains an acceptor substance for the aforementioned organic compound with high hole transport properties. It is also possible to use composite materials containing these substances.

[0136] Furthermore, by providing an electron injection buffer layer 206, the composite material layer 208 and the electron transport layer 2 Because the injection barrier between 05 and 05 can be relaxed, electrons generated in the composite material layer 208 can be injected It can be easily injected into the subtransport layer 205.

[0137] The electron injection buffer layer 206 contains alkali metals, alkaline earth metals, rare earth metals, and These compounds (alkali metal compounds (oxides such as lithium oxide, halides, carbon dioxide)) (including carbonates such as lithium and cesium carbonate), alkaline earth metal compounds (oxides, halogens) Compounds of rare earth metals (including oxides, halides, and carbonates), or compounds of rare earth metals (oxides, halides, and carbonates) It is possible to use materials with high electron injection capabilities, such as (including)).

[0138] Furthermore, the electron injection buffer layer 206 contains a material with high electron transport properties and a donor material, forming If performed, the mass ratio to a material with high electron transport properties should be between 0.001 and 0.1. It is preferable to add the donor substance in the following ratio. As for substances with high electron transport properties, first It can be formed using the same material as the electron transport layer 205 described above.

[0139] Furthermore, donor substances include alkali metals, alkaline earth metals, rare earth metals, and These compounds (alkali metal compounds (oxides, halides, lithium carbonates such as lithium oxide) (including carbonates such as um and cesium carbonate), alkaline earth metal compounds (oxides, halogenated Compounds of rare earth metals (including oxides, halides, and carbonates), or compounds of rare earth metals (including oxides, halides, and carbonates). In addition to )), tetratianaphthalene (abbreviation: TTN), nickerosene, decamethylnickerosene Organic compounds such as sen can also be used.

[0140] Furthermore, an electron relay layer 207 is placed between the electron injection buffer layer 206 and the composite material layer 208. It is preferable to form the electronic relay layer 207. The electronic relay layer 207 is not necessarily required, but it is preferable to form the electronic relay layer 207. By providing a highly transportable electron relay layer 207, electrons are supplied to the electron injection buffer layer 206. It will be possible to send it quickly.

[0141] An electron relay layer 207 is sandwiched between the composite material layer 208 and the electron injection buffer layer 206. The structure consists of an acceptor material contained in the composite material layer 208 and an electron injection buffer layer 20 The structure is such that it is less likely to interact with the donor substance contained in 6 and is less likely to inhibit each other's functions. Yes, it does. Therefore, it is possible to prevent an increase in the drive voltage.

[0142] The electron relay layer 207 contains a material with high electron transport properties, and the LUM of the material with high electron transport properties The O level interacts with the LUMO level of the acceptor material contained in the composite material layer 208, and electron transport. It is formed so as to be between the LUMO level of the highly electron-transporting material contained in layer 205.

[0143] Furthermore, if the electronic relay layer 207 contains a donor substance, the donor material of the donor substance The positions are the LUMO levels of the acceptor material in the composite material layer 208 and the electron transport layer 205 To ensure that the energy level is between that of the LUMO level of the highly electron-transporting material contained within. The LU value is the LU of the electron-transporting material contained in the electron relay layer 207. The MO level should be -5.0eV or higher, preferably -5.0eV to -3.0eV. stomach.

[0144] The electron relay layer 207 contains materials with high electron transport properties, such as phthalocyanine-based materials or It is preferable to use a metal complex having a metal-oxygen bond and an aromatic ligand.

[0145] The phthalocyanine-based materials included in the electron relay layer 207 are specifically CuPc and S nPc (Phthalocyanine tin(II) complex), ZnPc (Phthalocyanine zinc complex), CoPc (Cobal t(II)phthalocyanine, β-form), FePc(Phthal ocyanine Iron) and PhO-VOPc(Vanadyl 2,9,16, (23-tetraphenoxy-29H,31H-phthalocyanine) It is preferable to use either one.

[0146] As for metal complexes containing metal-oxygen bonds and aromatic ligands included in the electron relay layer 207, It is preferable to use a metal complex having a metal-oxygen double bond. Because it has acceptor properties (the property of readily accepting electrons), electron transfer (give and take) is efficient. This makes it easier. Furthermore, metal complexes containing a metal-oxygen double bond are considered stable. Therefore, by using a metal complex having a metal-oxygen double bond, the light-emitting element can be made lower This allows for more stable operation using voltage.

[0147] Phthalocyanine-based materials are preferred as metal complexes having a metal-oxygen bond and an aromatic ligand. Specifically, VOPc (Vanadyl phthalocyanine), SnO Pc(Phthalocyanine tin(IV) oxide complex) and TiOPc(Phthalocyanine titanium oxide co In either of the mplex groups, the metal-oxygen double bond acts on other molecules in terms of molecular structure. It is preferable because it is easy to implement and has high acceptability.

[0148] Furthermore, among the phthalocyanine-based materials mentioned above, those having a phenoxy group are preferred. Specifically, phthalocyanine derivatives containing a phenoxy group, such as PhO-VOPc, are preferred. It seems so. Phthalocyanine derivatives containing a phenoxy group are soluble in solvents. Therefore, It has the advantage of being easy to handle when forming light-emitting elements. Also, because it is soluble in solvents, It has the advantage of making maintenance of the equipment used for film deposition easier.

[0149] The electron relay layer 207 may further contain a donor substance. The donor substance may include: Alkali metals, alkaline earth metals, rare earth metals and their compounds (alkali metal compounds) (Oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate) (including), alkaline earth metal compounds (including oxides, halides, carbonates), or rare earth In addition to metal compounds (including oxides, halides, and carbonates), tetrathianaphthalene Organic compounds such as nickerosene and decamethylnickerosene can be used. By including these donor materials in the relay layer 207, electron movement becomes easier. This makes it possible to drive light-emitting elements at lower voltages.

[0150] When the electron relay layer 207 contains a donor substance, the above-mentioned substances are suitable for those with high electron transport properties. In addition to the materials mentioned, the acceptor levels of the acceptor material contained in the composite material layer 208 are Materials with high LUMO levels can be used. Specifically, the energy levels are as follows: , LUMO standard in the range of -5.0eV or higher, preferably -5.0eV to -3.0eV. It is preferable to use a substance having a position. Examples of such substances include perylene derivatives. Examples include nitrates and nitrogen-containing condensed aromatic compounds. Note that nitrogen-containing condensed aromatic compounds are nitrates. Because it is fixed, it is a preferred material to be used for forming the electronic relay layer 207. ru.

[0151] A specific example of a perylene derivative is 3,4,9,10-perylenetetracarboxylic acid dianhydride. Substance (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxylic bisbene Zoimidazole (abbreviation: PTCBI), N,N'-dioctyl-3,4,9,10-peri lentetracarboxylate diimide (abbreviation: PTCDI-C8H), N,N'-dihexyl- Examples include 3,4,9,10-perylenetetracarboxylate diimide (abbreviated as Hex PTC). It can be done.

[0152] Furthermore, a specific example of a nitrogen-containing condensed aromatic compound is pyrazino[2,3-f][1,10]. Phenanthroline-2,3-dicarbonitride (abbreviation: PPDN), 2,3,6,7,1 0,11-Hexacyano-1,4,5,8,9,12-Hexazatriphenylene (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) Examples include :F2PYPR).

[0153] Other examples include 7,7,8,8-tetracyanoquinodimethane (abbreviation: TCNQ), 1,4 ,5,8,-naphthalenetetracarboxylic dianhydride (abbreviation: NTCDA), perfluoro Pentacene, copper hexadecafluorophthalocyanine (abbreviation: F 16 CuPc), N,N' -Bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Pentadecaph Luoroctyl)-1,4,5,8-naphthalenetetracarboxylate diimide (abbreviation: NT) CDI-C8F), 3',4'-dibutyl-5,5''-bis(dicyanomethylene)-5 ,5''-dihydro-2,2':5',2''-terthiophene) (abbreviation: DCMT), Methanofullerene (e.g., [6,6]-phenyl C 61 Using methyl butyrate, etc. It is possible.

[0154] Furthermore, when the electron relay layer 207 contains a donor substance, a substance with high electron transport properties and a donor The electron relay layer 207 can be formed by methods such as co-deposition with a ionized material.

[0155] The hole injection layer 202, hole transport layer 203, light emission layer 204, and electron transport layer 205 are made of the aforementioned material. Each can be formed using the respective material. Thus, the EL layer 210 of this embodiment is fabricated. It is possible.

[0156] In the aforementioned light-emitting element, current flows due to the potential difference between the anode and cathode, and in the EL layer... The electrons and holes recombine, causing light to be emitted. This light is emitted at the anode or cathode. It is taken out to the outside through either one or both of the anode or cathode. Either one or both electrodes are transparent to visible light.

[0157] The configuration of the layer provided between the anode and cathode is not limited to those described above. To prevent quenching caused by the proximity of metal, parts away from the anode and cathode Any configuration other than the one described above is acceptable, as long as it includes a light-emitting region where holes and electrons recombine.

[0158] In other words, the layered structure is not particularly limited, and materials with high electron transport and hole transport properties are available. High-quality materials, materials with high electron injection capacity, materials with high hole injection capacity, bipolar materials (electron and A layer consisting of a material with high hole transport properties, or a hole-blocking material, etc., can be freely combined with the light-emitting layer. You can combine them to create the desired configuration.

[0159] Using the light-emitting element shown in this embodiment, a passive matrix type light-emitting device and a transient We will fabricate an active-matrix type light-emitting device in which the driving of the light-emitting elements is controlled by a stator. It is possible to do so. Furthermore, the light-emitting device can be applied to electronic equipment or lighting devices, etc. [Examples]

[0160] This example describes a light-emitting element according to one aspect of the present invention. The chemical composition of the material used in this example The formula is shown below.

[0161] [ka]

[0162] The following describes the method for manufacturing the light-emitting element 1 and the comparative light-emitting element 2 of this embodiment.

[0163] (light-emitting element 1) First, indium tin oxide (ITSO) containing silicon oxide is sputtered onto a glass substrate. A first electrode, which functions as an anode, was formed by depositing a film using the 3D method. The film thickness was 110n. Let m be the value, and the electrode area be 2 mm × 2 mm.

[0164] Next, as a pretreatment for forming light-emitting elements on the substrate, the substrate surface is washed with water, and 200 After baking at ℃ for 1 hour, UV ozone treatment was performed for 370 seconds.

[0165] Then, 10 -4 The substrate is introduced into the heating chamber of the vacuum deposition apparatus, where the internal pressure is reduced to approximately Pa. After vacuum firing at 170°C for 30 minutes, the substrate was allowed to cool for about 30 minutes.

[0166] Next, the substrate is introduced into the deposition chamber of the vacuum deposition apparatus, with the surface on which the first electrode is formed facing downwards. As shown, the substrate on which the first electrode is formed is fixed to a substrate holder provided inside the vacuum deposition apparatus. In this state, 10 -4 After reducing the pressure to approximately Pa, BPAFLP and oxidative stress are applied to the first electrode. A hole injection layer was formed by co-depositing molybdenum(VI). The thickness of this layer was 40 nm. The ratio of BPAFLP to molybdenum oxide is 4:2 by weight (=BPAFLP:Oxide It was adjusted to be molybdenum.

[0167] Next, BPAFLP is deposited on the hole injection layer to a thickness of 20 nm, and the hole transport layer is formed. It formed.

[0168] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2( dpm) was co-deposited to form a light-emitting layer on the hole transport layer. Here, 2mDBTPDBq -II, PCBNBB, and [Ir(mppr-Me)2(dpm)] have a weight ratio of 0.8 :0.2:0.05(=2mDBTPDBq-II:PCBNBB:[Ir(mppr- The settings were adjusted to be Me)2(dpm). The film thickness of the light-emitting layer was set to 40 nm.

[0169] Next, 2mDBTPDBq-II is deposited on the light-emitting layer to a thickness of 10 nm, and the first electric A sub-transport layer was formed.

[0170] Next, BPhen is deposited on the first electron transport layer to a thickness of 20 nm, and the second electron A transport layer was formed.

[0171] Furthermore, lithium fluoride (LiF) is deposited on the second electron transport layer to a thickness of 1 nm, and A sub-injection layer was formed.

[0172] Finally, as the second electrode that functions as the cathode, aluminum is used to a thickness of 200 nm. The light-emitting element 1 of this embodiment was fabricated by deposition in this manner.

[0173] (Comparison light-emitting element 2) The light-emitting layer of the comparative light-emitting element 2 consists of 2mDBTPDBq-II and [Ir(mppr-Me)2 It was formed by co-depositing (dpm)). Here, 2mDBTPDBq-II and [I The weight ratio of r(mppr-Me)2(dpm) is 1:0.05 (=2mDBTPDBq It was adjusted so that -II:[Ir(mppr-Me)2(dpm)]). Also, the emission The layer thickness was set to 40 nm. Except for the light-emitting layer, the device was fabricated in the same manner as light-emitting element 1.

[0174] In the vapor deposition process described above, resistance heating was used for all deposition steps.

[0175] Table 1 shows the element structures of the light-emitting element 1 and the comparative light-emitting element 2 obtained as described above. In this case, 2mDBTPDBq-II is an n-type host, PCBNBB is a p-type host, and [Ir (mppr-Me)2(dpm) is the guest. That is, in light-emitting element 1, n-type H In the case where both the host and the p-type host are located within the light-emitting layer, in the comparative light-emitting element 2, the p-type host is located within the light-emitting layer. It is not present in the light layer.

[0176] [Table 1]

[0177] These light-emitting elements are placed in a glove box under a nitrogen atmosphere, and the light-emitting elements are exposed to the air. After sealing the device to prevent leakage, measurements were taken to determine the operating characteristics of the light-emitting element. The measurements were taken at room temperature (in an atmosphere maintained at 25°C).

[0178] Figure 4 shows the current density-luminance characteristics of light-emitting element 1 and comparative light-emitting element 2. In Figure 4, the horizontal axis The current density is (mA / cm²). 2 The vertical axis represents luminance (cd / m²). 2 ) represents. Also, voltage-luminance characteristics The properties are shown in Figure 5. In Figure 5, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m²). 2 ) represents Furthermore, the luminance-current efficiency characteristics are shown in Figure 6. In Figure 6, the horizontal axis represents luminance (cd / m²). 2 )of The vertical axis represents the current efficiency (cd / A). Furthermore, the luminance-external quantum efficiency characteristics are shown in Figure 7. In figure 7, the horizontal axis represents luminance (cd / m²). 2 The vertical axis of the graph shows the external quantum efficiency (%).

[0179] Furthermore, the brightness of the light-emitting element 1 and the comparative light-emitting element 2 is 1000 cd / m². 2 Voltage in the vicinity (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A) Table 2 shows the power efficiency (lm / W) and external quantum efficiency (%).

[0180] [Table 2]

[0181] Furthermore, the emission spectra when a current of 0.1 mA is passed through light-emitting element 1 and comparison light-emitting element 2 are as follows: This is shown in Figure 8. In Figure 8, the horizontal axis represents wavelength (nm), and the vertical axis represents emission intensity (in arbitrary units). Also, as shown in Table 2, 1200 cd / m² 2 CIE chromaticity coordinates of light-emitting element 1 at this brightness The coefficient of flux is (x,y)=(0.56,0.44), and the density is 960 cd / m². 2 Comparison of light emission at this brightness level The CIE chromaticity coordinates of element 2 were (x,y)=(0.55,0.44). From this result, The light-emitting element 1 and the comparative light-emitting element 2 are derived from [Ir(mppr-Me)2(dpm)]. It was found that an orange emission was obtained.

[0182] As can be seen from Table 2 and Figures 4 to 7, the light-emitting element 1 has a current of the same value as the comparative light-emitting element 2. High values ​​were observed for efficiency, power efficiency, and external quantum efficiency. Generally, light from a light emitter When the material is extracted to the outside, total internal reflection occurs between the substrate and the atmosphere, affecting the internal quantum efficiency. It is estimated that only 25% to 30% of the light can be extracted to the outside.

[0183] Considering this, the internal quantum efficiency of comparative light-emitting element 2 is at best slightly less than 60%. It is estimated that the internal quantum efficiency of the light-emitting element 1 has increased to approximately 80%. Based on the above results, by applying one aspect of the present invention, it is possible to realize an element with high external quantum efficiency. It was shown that it is possible.

[0184] Next, reliability tests were conducted on light-emitting element 1 and comparative light-emitting element 2. The results of the reliability tests are shown in Figure 1. This is shown in Figure 9. In Figure 9, the vertical axis represents the normalized luminance (%) when the initial luminance is set to 100%. The horizontal axis represents the operating time (h) of the element. The reliability test was performed with an initial brightness of 5000 cd / m².2 to The settings were configured, and the light-emitting element 1 was driven under the condition of constant current density.

[0185] The brightness of comparative light-emitting element 2 after 120 hours was 58% of its initial brightness. The brightness of element 1 after 630 hours was 65% of the initial brightness. From this result, it can be concluded that the light-emitting element 1 It was found that this element has a longer lifespan compared to comparative light-emitting element 2. Based on the above results, It has been shown that a highly reliable element can be realized by applying one aspect of the invention. [Examples]

[0186] This example describes a light-emitting element according to one aspect of the present invention. The chemical composition of the material used in this example The chemical formula is shown below. Note that the chemical formulas of the materials used in the previous example are omitted.

[0187] [ka]

[0188] The method for fabricating the light-emitting element 3 in this embodiment is shown below.

[0189] (light-emitting element 3) First, ITSO is deposited on a glass substrate by sputtering, and the anode is formed. Electrode 1 was formed. The film thickness was set to 110 nm, and the electrode area was set to 2 mm × 2 mm. Ta.

[0190] Next, as a pretreatment for forming light-emitting elements on the substrate, the substrate surface is washed with water, and 200 After baking at ℃ for 1 hour, UV ozone treatment was performed for 370 seconds.

[0191] Then, 10 -4 A substrate is introduced into a vacuum deposition apparatus where the internal pressure is reduced to approximately Pa, and then vacuum deposition is performed. After vacuum firing at 170°C for 30 minutes in the heating chamber of the apparatus, the substrate is subjected to a 30-minute process. It was allowed to cool to a certain extent.

[0192] Next, the substrate on which the first electrode is formed is positioned so that the surface on which the first electrode is formed faces downwards. It is fixed to a substrate holder installed inside the air deposition apparatus, 10 -4 After reducing the pressure to approximately Pa, By co-depositing BPAFLP and molybdenum(VI) oxide onto electrode 1, a hole injection layer is formed. A film was formed. Its film thickness was 40 nm, and the ratio of BPAFLP to molybdenum oxide was by weight. The ratio was adjusted to 4:2 (=BPAFLP: molybdenum oxide).

[0193] Next, BPAFLP is deposited on the hole injection layer to a thickness of 20 nm, and the hole transport layer is formed. It formed.

[0194] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(dppm)2(aca c) was co-deposited to form a light-emitting layer on the hole transport layer. Here, 2mDBTPDBq-I The weight ratio of I, PCBNBB, and [Ir(dppm)2(acac)] is 0.8:0.2 :0.05(=2mDBTPDBq-II:PCBNBB:[Ir(dppm)2(ac The settings were adjusted to result in (ac)). The film thickness of the light-emitting layer was set to 40 nm.

[0195] Next, 2mDBTPDBq-II is deposited on the light-emitting layer to a thickness of 10 nm, and the first electric A sub-transport layer was formed.

[0196] Next, BPhen is deposited on the first electron transport layer to a thickness of 20 nm, and the second electron A sub-transport layer was formed.

[0197] Furthermore, an electron injection layer was formed by depositing LiF to a thickness of 1 nm on the second electron transport layer. .

[0198] Finally, as the second electrode that functions as the cathode, aluminum is used to a thickness of 200 nm. The light-emitting element 3 of this embodiment was fabricated by deposition in this manner.

[0199] In the vapor deposition process described above, resistance heating was used for all deposition steps.

[0200] Table 3 shows the element structure of the light-emitting element 3 obtained as described above.

[0201] [Table 3]

[0202] The light-emitting element 3 is placed in a glove box under a nitrogen atmosphere, so that the light-emitting element is not exposed to the atmosphere. After sealing the device, the operating characteristics of the light-emitting element were measured. The measurements were taken at room temperature (in an atmosphere maintained at 25°C).

[0203] Figure 10 shows the current density-luminance characteristics of the light-emitting element 3. In Figure 10, the horizontal axis represents the current density (m³). A / cm 2 The vertical axis represents luminance (cd / m²). 2 ) represents the voltage-luminance characteristics, which are shown in Figure 11. In Figure 11, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m²). 2 ) represents. Also, shine The luminance-current efficiency characteristics are shown in Figure 12. In Figure 12, the horizontal axis represents luminance (cd / m²). 2 ) on the vertical axis This represents the current efficiency (cd / A). The luminance-external quantum efficiency characteristics are shown in Figure 13. Figure 13 In this graph, the horizontal axis represents luminance (cd / m²). 2 The vertical axis of the graph shows the external quantum efficiency (%).

[0204] Furthermore, the brightness of the light-emitting element 3 is 1100 cd / m². 2 Voltage (V) and current density (mA) at that time / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W) The external quantum efficiency (%) is shown in Table 4.

[0205] [Table 4]

[0206] Furthermore, Figure 14 shows the emission spectrum when a current of 0.1 mA is passed through the light-emitting element 3. In figure 14, the horizontal axis represents wavelength (nm), and the vertical axis represents emission intensity (in arbitrary units). Also, in Table 4... As shown, 1100 cd / m² 2 The CIE chromaticity coordinates of light-emitting element 3 at this brightness are (x,y) = (0.54, 0.46). From this result, the light-emitting element 3 is [Ir(dppm)2 It was found that orange luminescence originating from (acac) was obtained.

[0207] As can be seen from Table 4 and Figures 10 to 13, the light-emitting element 3 has current efficiency, power efficiency, and external Each showed high quantum efficiency values. In particular, 1100 cd / m² 2 External quantum at brightness The efficiency was an extremely high 28%. This translates to an internal quantum efficiency of over 90%. Therefore, by applying one aspect of the present invention, it is possible to realize a device with high external quantum efficiency. It was shown that this is possible.

[0208] Next, a reliability test was performed on the light-emitting element 3. The results of the reliability test are shown in Figure 15. Figure 15 In this graph, the vertical axis represents the normalized brightness (%) when the initial brightness is set to 100%, and the horizontal axis represents the element's This indicates the operating time (h).

[0209] Reliability testing was performed with an initial brightness of 5000 cd / m². 2 Set to the following condition and the current density is constant for the light-emitting element. 3 was driven. Regarding the brightness after 320 hours, the light-emitting element 3 maintained 92% of its initial brightness. Based on the above results, it is possible to realize a highly reliable element by applying one aspect of the present invention. This was shown to be the case. [Examples]

[0210] The T1 level of an organic material can also be determined by optical measurements of the thin film or solution of that organic material. However, it can also be obtained by molecular orbital calculations. For example, to estimate the T1 level of an unknown material... Molecular orbital calculations can be used. In this example, Ir(dppm) is used as a guest. 2acac, Ir(mppr-Me)2dpm, 2mDBT used as an N-type host The T1 levels of PDBqII and PCBNBB used as a P-type host are calculated respectively. I took it out.

[0211] The calculation method is as follows: First, the singlet ground state (S0) and triplet state of each molecule are calculated. The most stable structure in the excited state (T1) was calculated using density functional theory (DFT). Furthermore, vibration analysis was performed in the most stable structures of S0 and T1, and the zero-point corrected energy was obtained. We calculated the T1 level from the zero-corrected energy difference between S0 and T1.

[0212] In calculations for N-type and P-type host molecules, 6-3 is used as the basis set for all atoms. 11G (triple split v using three shorting functions for each valence orbital) The basis functions of the Alence basis system were used. With the basis functions mentioned above, for example, in an H atom If so, the 1s-3s orbitals are considered, and for a carbon atom, the 1s-4s and 2p-4p orbitals are also considered. Orbitals will be taken into consideration. Furthermore, to improve calculation accuracy, H atoms will be used as the polarized ground system. The p function was added to the atoms, and the d function was added to all atoms except H. The B3LYP functional was used for exchange and The weights of each parameter related to correlation energy were defined.

[0213] For the guest molecule calculations, LanL2DZ was used as the basis set for the Ir atom. The basis set used was 6-311G. Furthermore, to improve calculation accuracy, the polarization basis set was used. The p-function was applied to the H atom, and the d-function to all other atoms. The functional B3PW91 was used. Then, the weights of each parameter related to exchange and correlation energy were defined.

[0214] The quantum chemistry calculation program used was Gaussian09. The calculation was performed using H This was performed using a high-performance computer (SGI Altix4700). .

[0215] The T1 level obtained by calculation is Ir(dppm)2acac is 2.13 electron volts. Ir(mppr-Me)2dpm is 2.13 electron volts, and 2mDBTPDBqII is 2. The readings were 42 electron volts for 42 electron volts and 2.31 electron volts for PCBNBB. These values ​​were obtained by optical measurement. It was similar to what was obtained from [another source].

[0216] Based on the above results, 2mDBTPDBqII is used as an N-type host, and P-type host The T1 level of PCBNBB used as the guest is Ir(dppm )2acac is more than 0.15eV higher than the T1 level of Ir(mppr-Me)2dpm It was found that, therefore, from the triplet excited state of the guest molecule, the N-type host molecule or P-type It can effectively prevent the host molecule from transitioning to a triplet excited state, resulting in high external quantum efficiency. This suggests that it is possible to obtain light-emitting elements.

[0217] Thus, the T1 levels obtained by optical measurements and the T1 levels obtained by molecular orbital calculations are very different. It is similar to this. Therefore, molecular orbital calculations can be performed without synthesizing new organic compounds. No, evaluate the T1 level of that organic compound and determine if that organic compound is useful in increasing luminescence efficiency. It is possible to determine whether or not this is true. [Explanation of symbols]

[0218] 101 circuit board 102 Emitting layer 103 First electrode 104 Second electrode 105 Injection layer of the first carrier 106 The first carrier's transport layer 107 Second carrier injection layer 108 Second Carrier Transport Layer 110 EL layer 110a EL layer 110b EL layer 111 Charge generation layer 201 Anode 202 Hole injection layer 203 Hole transport layer 204 Emitting layer 205 Electron transport layer 206 Electron injection buffer layer 207 Electron relay layer 208 Composite material layer 209 Cathode 210 EL layer

Claims

1. It comprises a first electrode, a second electrode, and a light-emitting layer. The light-emitting layer is located between the first electrode and the second electrode. Between the first electrode and the light-emitting layer, there is a first layer having an aromatic amine compound having a 9-phenylfluoren-9-yl group. The light-emitting layer comprises a phosphorescent compound, a first organic compound having electron transport properties, and a second organic compound having hole transport properties. The first organic compound and the second organic compound are a combination that forms an excited complex. The T1 level of the first organic compound is 0.15 electron volts or more greater than the T1 level of the phosphorescent compound. A light-emitting element wherein the T1 level of the second organic compound is 0.15 electron volts or more greater than the T1 level of the phosphorescent compound.

2. It comprises a first electrode, a second electrode, and a light-emitting layer. The light-emitting layer is located between the first electrode and the second electrode. Between the first electrode and the light-emitting layer, there is a first layer having an aromatic amine compound having a 9-phenylfluoren-9-yl group. The light-emitting layer comprises a phosphorescent compound, a first organic compound having electron transport properties, and a second organic compound having hole transport properties. The first organic compound and the second organic compound are a combination that forms an excited complex. The T1 level of the first organic compound is 0.15 electron volts or more greater than the T1 level of the phosphorescent compound. The T1 level of the second organic compound is 0.15 electron volts or more greater than the T1 level of the phosphorescent compound. A light-emitting element in which the emission spectrum of the excited complex and the absorption spectrum of the phosphorescent compound overlap.

3. In claim 2, The emission spectrum of the excited complex overlaps with the absorption band located at the longest wavelength end of the phosphorescent compound, thereby providing a light-emitting element.

4. It comprises a first electrode, a second electrode, and a light-emitting layer. The light-emitting layer is located between the first electrode and the second electrode. Between the first electrode and the light-emitting layer, there is a first layer having an aromatic amine compound having a 9-phenylfluoren-9-yl group. The light-emitting layer comprises an organometallic complex, a first organic compound having electron-transporting properties, and a second organic compound having hole-transporting properties. The first organic compound and the second organic compound are a combination that forms an excited complex. The T1 level of the first organic compound is 0.15 electron volts or more greater than the T1 level of the organometallic complex. A light-emitting element wherein the T1 level of the second organic compound is 0.15 electron volts or more greater than the T1 level of the organometallic complex.

5. It comprises a first electrode, a second electrode, and a light-emitting layer. The light-emitting layer is located between the first electrode and the second electrode. Between the first electrode and the light-emitting layer, there is a first layer having an aromatic amine compound having a 9-phenylfluoren-9-yl group. The light-emitting layer comprises an organometallic complex, a first organic compound having electron-transporting properties, and a second organic compound having hole-transporting properties. The first organic compound and the second organic compound are a combination that forms an excited complex. The T1 level of the first organic compound is 0.15 electron volts or more greater than the T1 level of the organometallic complex. The T1 level of the second organic compound is 0.15 electron volts or more greater than the T1 level of the organometallic complex. A light-emitting element in which the emission spectrum of the excited complex and the absorption spectrum of the organometallic complex overlap.

6. In claim 5, The emission spectrum of the excited complex overlaps with the absorption band located at the longest wavelength end of the organometallic complex, thereby providing a light-emitting element.

7. In any one of claims 1 to 6, The first layer is a light-emitting element in contact with the light-emitting layer.

8. In any one of claims 1 to 7, A light-emitting element in which at least one of the first organic compound and the second organic compound is a fluorescent compound.

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