Light-emitting element and light-emitting device

Abstract

To provide a light-emitting element with high external quantum efficiency.SOLUTION: A light-emitting element includes a light-emitting layer containing a guest, an n-type host, and a p-type host between a pair of electrodes. A value obtained by subtracting the energy difference between the ground state and the triplet excited state of the n-type host (or the p-type host) from the energy difference between the ground state and the triplet excited state of the guest is 0.15 eV or more. In the light-emitting element, the transition from the guest in the triplet excited state to the triplet excited state of the n-type host (or the p-type host) does not occur easily; therefore, the light emission from the guest in the triplet excited state occurs efficiently. The LUMO level of the n-type host is higher than the LUMO level of the guest by 0.1 eV or more. Alternatively, the HOMO level of the p-type host is lower than the HOMO level of the guest by 0.1 eV or more. In the light-emitting element, recombination of electrons and holes occurs in the guest efficiently and thus, the luminous efficiency or the external quantum efficiency can be increased.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Research and development of organic EL devices has been actively carried out (Patent Document 1, Non-Patent Document 1 and Non-Patent Document 2). (See Patent Document 2.) The basic structure of an organic EL element is a pair of electrodes between which a light-emitting organic compound It is a thin and lightweight device that sandwiches a layer containing With characteristics such as high speed response and low DC voltage drive, it is the next generation flat panel It is attracting attention as a display element. Ray also has the characteristics of excellent contrast and image quality, and a wide viewing angle. Since the EL element is a surface light source, it can be used as a light source for backlighting of LCD displays and lighting. Applications of this technology are also being considered.

[0003] The light-emitting mechanism of organic EL elements is a carrier injection type. In other words, the light-emitting layer is sandwiched between electrodes. By applying a voltage, electrons and holes injected from the electrode recombine to form a light-emitting material. The excited state is called the singlet excited state, and when the excited state returns to the ground state, light is emitted. The statistical generation ratio of the former and the latter in a light-emitting element is It is believed that the latter is one-third of the former. Unless otherwise specified, the singlet excited state (triplet excited state) refers to the singlet excited state (triplet excited state), It refers to the lowest energy level.

[0004] The ground state of luminescent organic compounds is usually a singlet state. Therefore, the singlet excited state The emission from triplet electrons is called fluorescence because it is an electron transition between the same spin multiplicity states. The light emitted from the excited state is called phosphorescence because it is an electron transition between different spin multiplicities. Here, a compound that emits fluorescence (hereinafter referred to as a fluorescent compound) usually emits phosphorescence at room temperature. Therefore, in a light-emitting device using a fluorescent compound, The theoretical limit of the internal quantum efficiency (the ratio of photons generated to injected carriers) is This is based on the ratio of the singlet excited state to the triplet excited state.

[0005] On the other hand, if a compound that emits phosphorescence (hereinafter referred to as a phosphorescent compound) is used, the internal quantum efficiency can be increased to 1 In theory, it is possible to increase the luminescence efficiency up to 0.00%. For this reason, in order to realize a highly efficient light-emitting device, In recent years, development of light-emitting elements using phosphorescent compounds has been actively pursued.

[0006] In particular, due to its high phosphorescence quantum efficiency, phosphorescent compounds with iridium as the central metal are Organometallic complexes have been attracting attention. For example, Patent Document 1 describes an organometallic complex having iridium as the central metal. Organometallic complexes containing the above-mentioned lanthanides have been disclosed as phosphorescent materials.

[0007] When the light-emitting layer of the light-emitting element is formed using the above-mentioned phosphorescent compound, the concentration quenching of the phosphorescent compound is To suppress quenching by light and triplet-triplet annihilation, the compound is placed in a matrix of other compounds. In most cases, the phosphorescent compound is dispersed in a matrix. The compound is called the host, and the compound dispersed in the matrix, such as a phosphorescent compound, is called the guest. can be.

[0008] The general elementary process of light emission in a light-emitting device that uses a phosphorescent compound as a guest is as follows: There are several, which are explained below.

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

[0010] In other words, in the direct recombination process (1) above, the intersystem crossing efficiency of the guest molecule and the phosphorescence High quantum efficiency will result in high luminous efficiency.

[0011] (2) When electrons and holes recombine in the host molecule, 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 guest molecule is higher than the T1 level of the host molecule, The excitation energy is transferred to the guest molecule, and the guest molecule enters a triplet excited state. The guest molecule in this state emits phosphorescence. Although energy transfer to the S level (S1 level) is also possible, in most cases the S level of the guest molecule The T1 level is located on the higher energy side than the T1 level of the host molecule, and the main energy Since this is unlikely to be a gye transfer process, we will omit it here.

[0013] (2-2) When the excited state of the host molecule is a singlet excited state, If the energy level (S1 level) of 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 The guest molecule in the triplet excited state emits phosphorescence. The guest molecule in the single excited state undergoes intersystem crossing to the triplet excited state and emits phosphorescence.

[0014] In other words, in the energy transfer process (2) above, the triplet excitation energy of the host molecule It is important to transfer both the singlet and singlet excitation energy to the guest molecule efficiently. This becomes:

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

[0016] <Energy transfer process> The energy transfer process between molecules is described in detail below.

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

[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 vibration between the molecule and the guest molecule. The host molecule transfers energy to the guest molecule through the vibrational resonance phenomenon, and the host molecule The guest molecule enters the excited state. The rate constant of the Förster mechanism is k h * →g of This is shown in equation (1).

[0019]

number

[0020] In formula (1), ν represents the frequency, and f' h (ν) is the normalized Emission spectrum (fluorescence spectrum when discussing energy transfer from singlet excited states, When discussing energy transfer from triplet excited states, it represents the phosphorescence spectrum, and ε g (ν ) represents the molar extinction coefficient of the guest molecule, N represents Avogadro's number, and n represents the refractive index of the medium. represents the rate of excitation, R represents the intermolecular distance between the host molecule and the guest molecule, and τ represents the measured excitation state. represents the lifetime of the electron state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, and φ represents the luminescence quantum efficiency (single When discussing energy transfer from single excited states, the fluorescence quantum efficiency is used, and when discussing energy transfer from triplet excited states, the fluorescence quantum efficiency is used. When discussing energy transfer, it stands for phosphorescence quantum efficiency, and K 2 is the ratio of the host molecule and the guest molecule This is a coefficient (0 to 4) that represents the orientation of the transition dipole moment. In the case of random orientation, K 2 =2 / 3.

[0021] Dexter mechanism (electron exchange interaction) The Dexter mechanism occurs when the host and guest molecules approach the effective contact distance where orbital overlap occurs. The energy is transferred through the exchange of electrons of the excited host molecule and the ground state guest molecule. -Transfer occurs. The rate constant of the Dexter mechanism is k h * →g is shown in equation (2).

[0022]

number

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

[0024] Here, the energy transfer efficiency from the host molecule to the guest molecule Φ ET is expressed by equation (3). It is thought that r is the emission process of the host molecule (from the singlet excited state of the host molecule). When discussing energy transfer, consider fluorescence and energy transfer from the triplet excited state of the host molecule. represents the rate constant of the phosphorescence (when discussing n is the rate of non-radiative processes (thermal deactivation and intersystem crossing) represents the degree constant, and τ represents the measured lifetime of the excited state of the host molecule.

[0025]

number

[0026] First, from equation (3), the energy transfer efficiency Φ ETTo increase the The rate constant k h * →g , other competing rate constants k r +k n (=1 / τ) The rate constant of the energy transfer, k h * →g Large In order to achieve this, from equations (1) and (2), the Förster mechanism and the Dexter mechanism In both of these mechanisms, the emission spectrum of the host molecule (energy from the singlet excited state) When discussing energy transfer, consider the fluorescence spectrum and energy transfer from triplet excited states. The phosphorescence spectrum in the case of a triplet) and the absorption spectrum of the guest molecule (usually phosphorescence, so It can be seen that a larger overlap with the energy difference between the excited state and the ground state is better.

[0027] For example, the energy difference between the triplet excited state and the ground state of the host molecule is More efficient excitation is achieved by selecting materials that overlap the energy difference between the excited state and the ground state. Energy transfer from the host to the guest occurs efficiently.

[0028] However, the energy transfer from the guest molecule in the triplet excited state to the host molecule in the ground state is The same phenomenon occurs in the host molecule. The energy difference between the triplet excited state and the ground state of the guest molecule overlaps with the energy difference between the triplet excited state and the ground state of the guest molecule. In the selected materials, the triplet excited states of the guest molecules are energetically coupled to the triplet excited states of the host molecules. This also means that energy transfer is more likely, resulting in a decrease in luminous efficiency.

[0029] To address this issue, for example, as described in Non-Patent Document 1, The energy difference between the triplet excited state and the ground state of the guest molecule is calculated by It has been proposed to overcome this by making the energy difference larger than that between the

[0030] In Non-Patent Document 1, the energy difference between the triplet excited state and the ground state of the host molecule is calculated as the guest molecule. The energy difference between the triplet excited state and the ground state of the host molecule is 0.3 eV (currently (currently corrected to 0.15 electron volts) increases the This prevents transition from the singlet 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 between the triplet excited state and the ground state of the acetylene molecule is at least 0.15 electron volts. This allows the transition from the triplet excited state of the guest molecule to that of the host molecule to be sufficiently accelerated. It can be prevented. [Prior art documents] [Patent documents]

[0032] [Patent Document 1] International Publication No. 2000 / 070655 Brochure [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). Summary of the Invention [Problem to be solved by the invention]

[0034] However, the difference in energy between the host and guest molecules means that the Förster mechanism and Dexter mechanism mentioned above are less likely to occur, This causes a problem of a decrease in luminous efficiency. The present invention provides a light-emitting device based on a new principle.

[0035] As mentioned above, there are various excitation processes, but the excitation process with less deactivation is direct deactivation. This is a recombination process, and improving this ratio will improve the luminous efficiency or external quantum efficiency. One aspect of the present invention is to provide a method for efficiently generating a direct recombination process. Another object of one embodiment of the present invention is to provide a light-emitting element with high external quantum efficiency. The goal is to [Means for solving the problem]

[0036] One embodiment of the present invention is a method for producing a phosphorescent compound (guest), a first organic compound, and a second organic compound. a light-emitting layer between a pair of electrodes, the light-emitting layer including a first organic compound and a second organic compound, The energy difference between the excited and ground states is the energy difference between the triplet excited state and the ground state of the guest. The light-emitting element is characterized in that the luminance is 0.15 eV or more higher than the reference luminance.

[0037] In the above, the first organic compound and the second organic compound form an exciplex. The first organic compound may have a higher electron transporting property than a hole transporting property. That is, the second organic compound may have a hole transporting property superior to an electron transporting property. In the case of a color, the first organic compound and the second organic compound are respectively an n-type host and a p-type This is called a type host.

[0038] In addition, one embodiment of the present invention is a light-emitting layer including a guest, an n-type host, and a p-type host, the light-emitting layer being disposed between a pair of electrodes. and the LUMO (Lowest Unoccupied Molecular Weight) of the n-type host The (ar Orbital) level is at least 0.1 electron volts higher than the LUMO level of the guest. The light-emitting device is characterized by the above.

[0039] If the LUMO level of the guest is too low compared to the LUMO level of the n-type host, the electrical conductivity will be poor. Therefore, the LUMO level of the n-type host, En, is shifted to the LUMO level of the guest. The value (En-Ea) minus Ea is 0.1 eV or more and 0.5 eV or less. It is preferable that

[0040] Furthermore, one embodiment of the present invention provides a light-emitting layer including a guest, an n-type host, and a p-type host, and a pair of electrodes. The HOMO (Highest Occupied Molecular Weight) of the p-type host is The lateral orbital level is more than 0.1 eV lower than the HOMO level of the guest The light-emitting element is characterized by the above.

[0041] If the HOMO level of the guest is too high compared to the HOMO level of the p-type host, the electrical conductivity will be affected. Therefore, the HOMO level Ep of the p-type host is shifted to the HOMO level of the guest. The value after subtracting Eb, (Ep-Eb) is between -0.5 and -0.1 eV It is preferable that:

[0042] In the light-emitting element, the guest is preferably an organometallic complex. In the present invention, at least one of the n-type host and the p-type host may be a fluorescent compound. The light-emitting element of one embodiment of the present invention can be applied to light-emitting devices, electronic devices, and lighting devices. do.

[0043] In one embodiment of the present invention, the light-emitting layer comprises an n-type host molecule, a p-type host molecule, and a guest molecule. Of course, the molecules do not need to be arranged in a regular pattern, and there can be very little regularity. In particular, when the light-emitting layer is a thin film of 50 nm or less, it becomes amorphous. Therefore, it is preferable to select a combination of materials that are difficult to crystallize. stomach.

[0044] In addition, one embodiment of the present invention is a semiconductor device in which a first electrode 103 is formed on a substrate 101 as shown in FIG. Alternatively, a light-emitting element may be provided in which the light-emitting layer 102 and the second electrode 104 having the above-described structure are stacked. Here, the first electrode 103 is one of an anode and a cathode, and the second electrode 104 is one of an anode and a cathode. It is the other extreme.

[0045] In addition, as shown in FIG. 1B, one embodiment of the present invention is a light-emitting device including a first electrode 103, a light-emitting layer 102, and a light-emitting layer 103. In addition to the second electrode 104, a first carrier injection layer 105, a first carrier transport layer 106, a second carrier injection layer 107, and a second carrier transport layer 108 are provided in layers. The light-emitting device may be a light-emitting device, in which the first carriers are either electrons or holes, and the second carriers are If the first electrode is an anode, the first carrier is a hole. If the first electrode is a cathode, the first carriers are electrons. [Effects of the Invention]

[0046] In one embodiment of the present invention, triplet excited states of host (n-type host and p-type host) molecules and radicals are The energy difference between the triplet excited state and the ground state of the guest molecule is By increasing the electron volt density by 0.15 eV or more, the triplet excited state of the guest molecule is converted to the host (n The transition of the molecules (type host and p-type host) to the triplet excited state can be sufficiently prevented. This makes it possible to provide a light-emitting device with high external quantum efficiency.

[0047] On the other hand, for energy transfer processes using the Förster and Dexter mechanisms, The process of energy transfer from the exciplex of n-type host molecules and p-type host molecules to the guest molecules The exciplex is formed when the energy is transferred to the guest molecule. The triplet state of the n-type host molecule (or p-type host molecule) 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 the energy difference is more than 0.15 eV, the triplet excited state of the guest molecule is n-type hole. There is no energy transfer to the triplet excited state of the host molecule (or p-type host molecule). .

[0048] In one embodiment of the present invention, for example, the LUMO level of the n-type host molecule is higher than the LUMO level of the guest molecule. Electrons that have been conducted by n-type host molecules because they are more than 0.1 eV higher than the MO level preferentially enters the LUMO level of the guest molecule, resulting in the guest molecule becoming an anion. , attracts holes, and the holes and electrons recombine in the guest molecules.

[0049] In one embodiment of the present invention, for example, the HOMO level of the p-type host molecule is higher than the HO of the guest molecule. Holes conducted by p-type host molecules due to being more than 0.1 eV below the MO level preferentially enters the HOMO level of the guest molecule, resulting in the guest molecule becoming a cation. , attracts electrons, and the holes and electrons recombine in the guest molecules.

[0050] In this way, by using one embodiment of the present invention, it is possible to efficiently add a carrier to a guest molecule. In particular, in one aspect of the present invention, the ratio of the direct recombination process can be increased by injecting the Since the layer uses a mixture of n-type and p-type hosts, electrons are conducted through the n-type host molecules. As a result, the hole tends to conduct through the p-type host molecule. The electrons are injected from the n-type host molecule, and the HOMO level of the guest molecule is Holes are injected from the molecules. [Brief explanation of the drawings]

[0051] [Figure 1] 1A-1C illustrate various aspects of the present invention. [Figure 2] 1A to 1C illustrate the principle of one embodiment of the present invention. [Figure 3]1A to 1C illustrate the principle of one embodiment of the present invention. [Figure 4] FIG. 10 is a graph showing current density-luminance characteristics of the light-emitting element of Example 1. [Figure 5] FIG. 10 is a graph showing voltage-luminance characteristics of the light-emitting element of Example 1. [Figure 6] FIG. 10 shows luminance-current efficiency characteristics of the light-emitting element of Example 1. [Figure 7] FIG. 1 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 1. [Figure 8] FIG. 2 shows an emission spectrum of the light-emitting element of Example 1. [Figure 9] 10 shows the results of a reliability test of the light-emitting element of Example 1. FIG. [Figure 10] FIG. 10 is a graph showing current density-luminance characteristics of the light-emitting element of Example 2. [Figure 11] FIG. 10 is a graph showing voltage-luminance characteristics of the light-emitting element of Example 2. [Figure 12] FIG. 10 shows luminance-current efficiency characteristics of the light-emitting element of Example 2. [Figure 13] FIG. 10 is a graph showing luminance-external quantum efficiency characteristics of the light-emitting element of Example 2. [Figure 14] FIG. 10 shows an emission spectrum of the light-emitting element of Example 2. [Figure 15] 10 shows the results of a reliability test of the light-emitting element of Example 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0052] The embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description. The present invention is not limited to the above embodiments, and various changes and modifications may be made in the form and details thereof without departing from the spirit and scope of the present invention. It will be readily understood by those skilled in the art that the present invention can be achieved by the following embodiments. It should not be construed as being limited to the contents of the description. The same reference numerals are used in different drawings to denote the same parts or parts having similar functions. A repeated explanation will be omitted.

[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 it 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 There is only one electron (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 cation.

[0057] Electrons and holes are transported by hopping between these n-type and p-type host molecules. As shown in Figure 2(B), an electron is added to the LUMO of the guest molecule, and a hole is added to the HOMO. is injected (direct recombination process), and the guest molecule enters an excited state (intramolecular exciton, exciton) In this way, even in the direct excitation recombination process, the guest atoms are generated especially from the n-type and p-type hosts. The phenomenon in which carriers are injected directly into the gate is called Guest Coupled with Co Complementary Hosts (GCCH).

[0058] As is clear from Figure 2, the difference between the LUMO level and the HOMO level of the n-type host molecule is The difference between the LUMO level and the HOMO level of the p-type host molecule is the LU of the guest molecule. Since the difference is much larger than the difference between the MO level and the HOMO level, the Förster mechanism and the Dexter mechanism The triplet excited state of the guest is converted to the triplet excited state of the n-type host or p-type host by The probability of migration is small enough.

[0059] That is, as shown in FIG. 2(C), the group of the guest molecule G and the n-type host molecule H_n_1 When the bottom states (S0_G, S0_H_n_1, respectively) are taken as the reference, the n-type host molecule H The triplet excited state energy level T1_H_n_1 of _n_1 is the triplet excited state energy level of the guest molecule G. Since the energy level of the excited state is higher than that of T1_G by ΔEt (≧0.15 eV), The transition between these two states is unlikely to occur at room temperature. are the energies of the singlet excited states of the guest molecule G and the n-type host molecule H_n_1, respectively. It is ranked second.

[0060] In Figure 2(C), the energy state of the n-type host molecule was described. The energy level of the triplet excited state is the same as that of the guest molecule. A similar effect can be obtained if the level is higher than the standard.

[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. Although it is not an energy difference with the state, there is a certain correlation. Cetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) Ir(dppm)2(acac) is used as a guest, but its HOMO The difference between the triplet excited state and the LUMO level is 2.58 eV, while the difference between the triplet excited state and the radical The energy difference with the bottom state is 2.22 eV. 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxa Sarin (abbreviated as 2mDBTPDBq-II) has 3.10 electron volts and 2.5 electron volts, respectively. 4 electron volts, and is used as a p-type host. '-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PC BNBB) are 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 the n-type host is 2mDBTPDBq-II, when PCBNBB was used as the p-type host, 2mDBTP Energy difference between the triplet excited state and the ground state of DBq-II and the triplet state of PCBNBB The energy difference between the excited state and the ground state (as a result of optical measurements) is 2.54 electron bosons, respectively. volt, 2.40 eV) is the energy difference between the triplet excited state and the ground state of the guest ( The optical measurement results show that the electron density is 0.18 electron volts higher than the 2.22 electron volts. The triplet excited state of the cation is hardly transferred to the host.

[0063] In addition, (dipivaloylmethanato)bis(3,5-dimethyl-2-phenylpyridinyl) Radinato)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]) The triplet excited state and ground state of [Ir(mppr-Me)2(dpm)] can also be used. The energy difference between this state and the other state is 2.24 eV, as determined by optical measurements.

[0064] Therefore, 2mDBTPDBq-II was used as the n-type host and PCBNB was used as the p-type host. When B is used, the energy difference between the triplet excited state 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 energy is more than 1 electron volt higher, the triplet excited state of the guest is hardly transferred to the host.

[0065] The above is a direct recombination process in which electrons and holes are injected into the guest. The host molecule forms an exciplex, which transfers energy to the guest molecule, The guest molecule can also be in an excited state. In this case, the energy transfer involves Use the Star or 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

[0068] 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.

[0069] <<Electroplex>> In this specification, an electroplex refers to the direct formation of an exciplex from the ground-state n-type host and the ground-state p type host. As described above, in the Förster mechanism and the Dexter mechanism, when electrons and holes recombine in the host,

[0070] the excitation energy moves from the excited-state host to the guest, and the guest reaches the excited state and emits light.

[0071] ​​ Here, the host itself emits light before the excitation energy is transferred from the host to the guest. loses some of its excitation energy by converting it to thermal energy. When the electron is in the singlet excited state, the excited lifetime is shorter than when it is in the triplet excited state. Therefore, the deactivation of singlet excitons is likely to occur. The deactivation of excitons leads to a decrease in the life of the light-emitting element. This is one of the reasons why it continues.

[0072] On the other hand, in one embodiment of the present invention, the n-type host and the p-type host are present in the same light-emitting layer, so that n The p-type and p-type host molecules are in a carrier state (anion and cation). Therefore, n-type hosts with short excitation lifetimes often form electroplexes. Singlet excitons of molecules or p-type host molecules are unlikely to be formed.

[0073] In other words, the process of directly forming an exciplex without forming singlet excitons of individual molecules. This also makes it possible to suppress the deactivation of the singlet excitons. The resulting electroplex transfers energy to the guest, resulting in high luminescence efficiency. Therefore, a light-emitting element with a good light-emitting property can be obtained.

[0074] <Exciplex formation by excitons> Another process is when one of the n-type and p-type host molecules is single. After forming a first exciton, the elementary process of interaction with the other ground state to form an exciplex is considered. Unlike electroplexes, in this case, once an n-type host molecule or p-type Singlet excitons are generated in the host molecule, but if they can be quickly converted into an exciplex, If the n-type phosphide is used, the deactivation of singlet excitons can be suppressed. This process is less likely to occur when the dopant 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. When the difference between the HOMO level and the LUMO level of these compounds is large, When the difference is 0.3 eV or more, electrons preferentially enter the n-type host molecule, and holes preferentially enter the n-type host molecule. First, the electron enters the p-type host molecule. In this case, the exciplex is formed via a singlet exciton. It is believed that the process of electroplex formation takes precedence over the process of ionization.

[0076] By the way, the energy transfer from the exciplex formed as 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 is It is preferable that the energy difference between the triplet excited state and the ground state of the molecule is small.

[0077] In this case, the energy difference between the triplet excited state and the ground state of the exciplex is This corresponds to the difference between the LUMO level of the guest molecule and the HOMO level of the p-type host molecule. When the difference between the MO level and the HOMO level is equal to or close to the The guest molecule can be brought into a triplet excited state, and the exciplex itself is in the ground state.

[0078] However, since the exciplex is stable only in the excited state, when it returns to the ground state, the n-type host molecule The triplet excited state and the ground state are then separated into the triplet excited state and the p-type host molecule. The energy difference between the triplet excited state and the ground state of the guest molecule is Because the triplet excited state of the guest molecule is large, energy transfer occurs to one of the host molecules. This is extremely unlikely to occur at room temperature.

[0079] (Embodiment 2) In this embodiment, the principle of a light-emitting element of one embodiment of the present invention will be described with reference to FIGS. 3(A) shows two n-type host molecules (H_n_1, H_n_2) and one guest molecule (G). and when two p-type host molecules (H_p_1, H_p_2) are aligned in a straight line, The energy distribution of the molecules shown here is as follows. Each molecule has its own HOMO and LUMO.

[0080] Here, the LUMO level En of the n-type host molecule is 0.5 lower than the LUMO level Ea of the guest molecule. The HOMO level Ep of the p-type host molecule is higher than that of the guest molecule by more than 1 electron volt. The difference between the LUMO level and the HOMO level of the n-type host molecule is The difference between the LUMO level and the HOMO level of the p-type host molecule is the LUMO of the guest molecule. It is preferably 0.5 eV or more larger than the difference between the O level and the HOMO level.

[0081] As shown in Figure 3(A), holes are injected from the anode (right side of the figure) and electrons are injected from the cathode (left side of the figure). Since the n-type host molecule H_n_1 has an electron in the LUMO, the p-type host molecule H _p_1 is in a state where there is only one HOMO electron (one hole). The n-type host molecule H_n_1 is an anion, and the p-type host molecule H_p_1 is a cation. It is.

[0082] Electrons and holes are transported by hopping between these n-type and p-type host molecules. As shown in the figure, the LUMO level of the p-type host molecule is higher than that of the n-type host molecule. Since the HOMO level of the n-type host molecule is higher than that of the n-type host molecule, electrons are conducted through the n-type host molecule. is lower than the HOMO level of the p-type host molecule, so holes are conducted through the p-type host molecule.

[0083] Then, as shown in Figure 3(B), an electron is injected into the LUMO of the guest molecule, becomes an anion. Here, the LUMO level of the n-type host molecule is the LUMO level of the guest molecule. The LUMO level of the p-type host molecule is, of course, even higher. Then, the electron that has entered the LUMO of the guest molecule becomes metastable, so to speak, It becomes trapped in the molecule.

[0084] As a result, the guest molecule becomes a negatively charged anion, which attracts surrounding holes. Therefore, as shown in Figure 3(C), A hole in the p-type host molecule H_p_2 is injected into the guest molecule G. The Coulomb interaction is Since it extends relatively far, electrons and holes are efficiently collected within the guest molecules.

[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 The electron in the LUMO of the guest molecule G recombines with the hole in O (i.e., the electron in the LUMO of the guest molecule G recombines with the hole in O) HOMO of the molecule H_p_2, or the HOMO of the p-type host molecule H_p_2 When the hole at G moves to the LUMO of the guest molecule G, light is emitted.

[0086] If the electron transfer is prohibited, the hole in the HOMO of the p-type host molecule H_p_2 is transferred to the HOMO of the guest molecule G, and the guest molecule G enters an excited state. The electron G transitions to the ground state, emitting light in the process.

[0087] To attract holes to the guest through Coulomb interaction, (HOMO level of p-type host) (HOMO level of guest) = ΔEp, (LUMO level of n-type host) - (LUMO level of guest) When the electron volts (electron volts) are ΔEn, ΔEp<ΔEn+0.2 [electron volts], preferably, Δ It is recommended that 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 is If it is neutral, the HOMO level of the guest molecule is lower than that of the p-type host molecule. Therefore, it is unlikely that holes will be injected into the guest molecules.

[0089] In Figure 3, the LUMO level En of the n-type host molecule is higher than the LUMO level Ea of the guest molecule. In addition, when 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 higher than the HOMO level Eb of the guest molecule. The LUMO level En of the n-type host molecule is 0.1 eV or more lower than that of the guest molecule. The same principle applies to guest molecules even when the LUMO level is 0.1 electron volts or more lower than Ea. In this case, the hole is first injected into the HOMO of the guest molecule. The Coulomb interaction then injects electrons into the guest molecule.

[0090] The LUMO level En of the n-type host molecule is higher than the LUMO level Ea of the guest molecule. In addition, when the HOMO level Ep of the p-type host molecule is lower than the HOMO level Eb of the guest molecule, In this case, the guest can be more efficiently injected with charge and placed in an excited state. The LUMO level En of the n-type host molecule is at least 0.1 lower than the LUMO level Ea of the guest molecule. or more electron volts higher, or the HOMO level Ep of the p-type host molecule is higher than the HOMO level of the guest molecule It is preferably at least 0.1 eV lower than Eb.

[0091] In addition, when an anionized n-type host molecule and a cationized p-type host molecule are adjacent to each other, In this case, both molecules may be in an excited complex state. To achieve this, the energy transfer process described above must be carried out. 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 It is better if the energy difference is as close as possible.

[0092] If the LUMO level of the n-type host molecule is 0.1 electron volts higher than the LUMO level of the guest molecule, If the HOMO level of the p-type host molecule is higher than that of the guest molecule by 0. Select a material that is one electron volt lower than the excited state of the exciplex and measure the energy difference between the excited and ground states. The energy difference between the triplet excited state and the ground state of the guest molecule is as close as possible to the energy difference. We should make it so that it becomes

[0093] Specifically, the LUMO approximation of [Ir(dppm)2(acac)] used as a guest The HOMO level is -2.98 eV and -5.56 eV, respectively. In addition, 2mDBTPDBq-II used as an n-type host had a valence of -2.78 The electron volts are -5.88 electron volts, and PCBNBB, which is used as a p-type host, is , -2.31 electron volts and -5.46 electron volts, respectively.

[0094] In this combination, the LUMO level of the guest is the same as that of the n-type and p-type hosts. MO level, and in particular, 0.2 eV lower than the LUMO level of the n-type host. The guest molecule tends to trap electrons and become an anion. Although it is higher than the HOMO level of the n-type host molecule, it is lower than the HOMO level of the p-type host molecule. 0.1 electron volts lower.

[0095] Therefore, as shown in Figure 3, an electron is first injected into the LUMO of the guest, and then the Holes are injected into the guest by the Ron interaction, resulting in light emission.

[0096] The LUMO level of [Ir(mppr-Me)2(dpm)] is -2.77 electron volts. The LUMO level (-2.78 electron boson) of the n-type host (2mDBTPDBq-II) The HOM of [Ir(mppr-Me)2(dpm)] is almost the same as that of [Ir(mppr-Me)2(dpm)]. The O level is -5.50 eV, which is the HOMO level of the p-type host (PCBNBB) (- 0.07 electron volts lower than the ion concentration (5.43 electron volts).

[0097] These values ​​indicate that [Ir(mppr-Me)2(dpm)] is a suitable host for the above n-type and p-type When used with [Ir(dppm )2(acac)].

[0098] (Embodiment 3) In this embodiment, a light-emitting element of one embodiment of the present invention will be described with reference to FIG. 1(B) is a light-emitting element having an EL layer 110 between a first electrode 103 and a second electrode 104. The light-emitting element in FIG. 1(B) is a diagram showing a light-emitting element in which layers are stacked in order on a first electrode 103. The first carrier injection layer 105, the first carrier transport layer 106, the light emitting layer 102, the first A second carrier transport layer 108, a second carrier injection layer 107, and a The EL layer 110 is composed of a first electrode 104 in addition to the light-emitting layer 102. A carrier injection layer 105, a first carrier transport layer 106, a second carrier transport layer 10 8 and the second carrier injection layer 107. The EL layer 110 is not necessarily composed of these. It is not necessary to have all of these layers.

[0099] Here, the first electrode 103 is either an anode or a cathode, and the second electrode 104 is either an anode or a cathode. The first carrier is either a hole or an electron, and the second carrier is either a hole or an electron. The carriers are either holes or electrons. If the first electrode is an anode, the first The carriers are holes, and if the first electrode is a cathode, 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. The first carrier transport layer 106 and the second carrier transport layer 108 are either of the transport layers. is either a hole transport layer or an electron transport layer.

[0100] The anode is made of metals, alloys, and conductive compounds with a large work function (specifically, 4.0 eV or more). It is preferable to use materials such as indium oxide and mixtures thereof. Indium-tin oxide (ITO), silicon or silicon oxide Indium oxide-tin oxide, indium oxide-zinc oxide (Indium Zinc Indium oxide containing tungsten oxide and zinc oxide (IWZO) These conductive metal oxide films are usually formed by sputtering. However, it may also be produced by applying a sol-gel method or the like.

[0101] For example, an indium oxide-zinc oxide film is made of indium oxide with 1 to 20 wt% zinc oxide. It can be formed by sputtering using a target containing lead. The WZO film is made of indium oxide with 0.5 to 5 wt% tungsten oxide and 0.0 wt% zinc oxide. It can be formed by sputtering using a target containing 0.1 to 1 wt% of Other materials include graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, and iron. , cobalt, copper, palladium, or nitrides of metal materials (for example, titanium nitride), etc. can be.

[0102] However, the layer of the EL layer 110 formed in contact with the anode is an electron acceptor and an organic compound, which will be described later. When a composite material containing a cathode and an acceptor is used, the cathode is The materials used include various metals, alloys, electrically conductive compounds, and A mixture of these may be used. For example, aluminum, silver, aluminum An alloy containing Al (e.g., Al-Si) can also be used. The film can be formed by a coating method, a vapor deposition method (including a vacuum deposition method), or the like.

[0103] The cathode is made of a metal, alloy, or electrically conductive compound with a small work function (preferably 3.8 eV or less). It is preferable to form the material using a material selected from the group consisting of the elements of the periodic table, and mixtures thereof. Elements belonging to Group 1 or 2, i.e., alkali metals such as lithium and cesium, and alkaline earth metals such as calcium and strontium, magnesium, and alloys (e.g., Mg-Ag, Al-Li), rare earth elements such as europium and ytterbium In addition to metals and alloys containing these, aluminum, silver, etc. can also be used.

[0104] However, the layer of the EL layer 110 formed in contact with the cathode is made of an organic compound and an electron When using a composite material that is mixed with a donor, 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 A sputtering method can be used. When silver paste or the like is used, a coating method can be used. or an ink jet method can be used.

[0105] The hole injection layer is a layer containing a substance with high hole injection properties. Molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide Chromium oxide, Zirconium oxide, Hafnium oxide, Tantalum oxide, Silver oxide Metal oxides such as tungsten oxide and manganese oxide can be used. Phthalocyanine (abbreviated as H2Pc), copper(II) phthalocyanine (abbreviated as CuPc), etc. Phthalocyanine compounds can be used.

[0106] In addition, the low molecular weight organic compound 4,4',4''-tris(N,N-diphenylamino) ) triphenylamine (abbreviation: TDATA), 4,4',4''-tris[N-(3-methylphenyl) (N-phenylamino)triphenylamine (abbreviation: MTDATA), 4 ,4'-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl DPAB, 4,4'-bis(N-{4-[N'-(3-methylphenyl)- N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated as DNTP D), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino] 3-[N-(9-phenylcarbazol-3-yl)benzene (abbreviation: DPA3B) )-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3, 6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9- Phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-( 9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: P Aromatic amine compounds such as CzPCN1) can be used.

[0107] Furthermore, polymeric compounds (oligomers, dendrimers, polymers, etc.) can also be used. For example, poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriflate) Phenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenyl (N'-phenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide (abbreviation: PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bi Examples include polymer compounds such as [poly(phenyl)benzidine] (abbreviation: Poly-TPD). In addition, poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS), polyaniline / poly(styrene sulfonate) (PAni / PS A polymer compound to which an acid such as methyl methyl stearate (S) is added can be used.

[0108] In addition, the hole injection layer may be a composite layer made by mixing an organic compound and an electron acceptor. Such composite materials are formed by the electron acceptor transferring holes to the organic compound. In this case, the organic compound is preferably a material that is excellent in transporting generated holes (a substance with high hole transporting properties).

[0109] The organic compounds used in the composite materials include aromatic amine compounds, carbazole derivatives, aromatic Various compounds such as aromatic hydrocarbons and polymer compounds (oligomers, dendrimers, polymers, etc.) As the organic compound used for the composite material, a compound having a high hole transporting property can be used. It is preferable that the organic compound is a low-molecular-weight organic compound. -6 cm 2 Hole transfer above / Vs However, it is preferable that the material has a higher hole transporting property than the electron transporting property. In the following, organic compounds that can be used in composite materials will be described. The compounds are specifically listed below.

[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 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation: CzPA), 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl] phenyl]-9H-carbazole (abbreviation: PCzPA), 1,4-bis[4-(N-carbazole) Carbazole derivatives such as [2,3,5,6-tetraphenyl]-2,3,5,6-zolylphenyl can be used.

[0111] In addition, 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t- BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9 ,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-t ert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: tB uDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10- Diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene ( Abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA), 9,10-bis[2-(1-naphthyl)phenyl]-2-tert -butylanthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene , 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, and other aromatic compounds Aromatic hydrocarbon compounds can be used.

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

[0113] The electron acceptor is 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroethylene. Organic compounds such as fluoroquinodimethane (abbreviated as F4-TCNQ) and chloranil, and transition metals In addition, metal oxides belonging to groups 4 to 8 of the periodic table can be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, Chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are electrically Among them, molybdenum oxide is particularly stable in the atmosphere and has a high molecular acceptability. It is preferred because it has low moisture content and is easy to handle.

[0114] In addition, the above-mentioned polymer compounds such as PVK, PVTPA, PTPDMA, and Poly-TPD A composite material may be formed using the above-mentioned electron acceptor and used in the hole injection layer.

[0115] The hole transport layer is a layer containing a substance with high hole transport properties. NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluorene- 2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), 4,4'-biphenyl bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl Aromatic amine compounds such as bis(2-methyl-2-phenylpropanol) (abbreviation: BSPB) can be used. The substance is mainly 10 -6 cm 2 A material with a hole mobility of 1 / Vs or more. Any other substance may be used as long as it has a higher hole transporting property than the above. The layer containing the highly permeable substance is not only a single layer, but also a laminate of two or more layers of the above substance. It may also be the same as the above.

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

[0117] In addition, the hole transport layer is made of 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 substance. The n-type host ( Alternatively, two or more p-type hosts can be used.

[0119] As the phosphorescent compound, an organometallic complex is preferred, and an iridium complex is particularly preferred. Considering the energy transfer by the Förster mechanism described above, the longest wavelength of the phosphorescent compound The molar absorption coefficient of the absorption band located on the long side is 2000M -1 ·cm -1 More than 5 is preferable. 000M -1 ·cm -1 The above is particularly preferred.

[0120] Examples of compounds having such a large molar absorption coefficient include [Ir(mppr-M e)2(dpm)] and [Ir(dppm)2(acac)]. [Ir(dppm)2(acac)] has a molar extinction coefficient of 5000M -1 ·cm - 1 By using materials that achieve this or higher, it is possible to obtain a light-emitting device with an external quantum efficiency of approximately 30%. .

[0121] As an n-type host, for example, in addition to the above-mentioned 2mDBTPDBq-II, 2-[4-( 3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]ky Noxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophene-4- (yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II) , and 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]ky Compounds that readily accept electrons, such as noxaline (abbreviation: 6mDBTPDBq-II) Either one of them can be used.

[0122] In addition to the above-mentioned PCBNBB, 4,4'-bis[N-(1-naphthalene) [alpha]-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), and 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenyla A compound that readily accepts holes, such as PCBA1BP, can be used. However, the present invention is not limited to these, and may be embodied in any of the following embodiments: Any combination of an n-type host and a p-type host that satisfies the relationship of the energy levels described above may be used.

[0123] The electron transport layer is a layer containing a substance with high electron transport properties. Alq3, tris(4-methyl-8-quinolinolato)aluminum (abbreviated as Almq3) , bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq2), BAlq, Zn(BOX)2, bis[2-(2-hydroxyphenyl)benzothiazol- ] zinc (abbreviated as Zn(BTZ)2) and other metal complexes.

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

[0125] In addition, poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexyl) PF -Py), poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2 '-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy) The substances mentioned here are mainly 10 -6 cm 2 Electron mobility above / Vs It should be noted that, as long as the substance has a higher electron transporting property than the hole transporting property, other substances than those mentioned above can be used. The material may also be used as an electron transport layer.

[0126] The electron transport layer may be a single layer or a laminate of two or more layers made of the above-mentioned materials. It may also be possible to

[0127] The electron injection layer is a layer containing a substance with high electron injection properties. Umium, calcium, lithium fluoride, cesium fluoride, calcium fluoride, lithium oxide Alkali metals, alkaline earth metals, or compounds thereof, such as those mentioned above, can be used. Also, rare earth metal compounds such as erbium fluoride can be used. The above-mentioned materials for forming the electron transport layer can also be used.

[0128] Alternatively, the electron injection layer may be a composite material obtained by mixing an organic compound and an electron donor. Such a composite material is formed by electron generation in an organic compound by an electron donor. In this case, the organic compound is a fluorine-containing compound. It is preferable that the material is excellent in transporting the generated electrons. Specifically, for example, the above-mentioned electron Materials that form the transport layer (such as metal complexes and heteroaromatic compounds) can be used.

[0129] The electron donor may be any substance that exhibits electron donating properties to organic compounds. Alkali metals, alkaline earth metals and rare earth metals are preferred, and lithium, cesium, magnesium Examples include nesium, calcium, erbium, and ytterbium. Metal oxides and alkaline earth metal oxides are preferred, and lithium oxide, calcium oxide, barium oxide, etc. Also, Lewis bases such as magnesium oxide can be used. It is also possible to use organic compounds such as tetrathiafulvalene (TTF). can.

[0130] The hole injection layer, the hole transport layer, the light emitting layer 102, the electron transport layer, and the electron injection layer are Each of these can be formed by a deposition method (including vacuum deposition), an inkjet method, a coating method, etc. This can be done.

[0131] As shown in FIG. 1C, a plurality of EL layers 110a and 110b are provided between the anode and the cathode. In this case, the EL layers 110a and 110b each have at least one light-emitting element. Between the stacked first EL layer 110a and second EL layer 110b, a charge It is preferable to provide a charge generation layer 111. The charge generation layer 111 is preferably formed from the above-mentioned composite material. The charge generating layer 111 can be formed by stacking a layer made of a composite material and a layer made of another material. It may also have a layered structure.

[0132] In this case, the layer made of another material includes a material having an electron donating property and a material having a high electron transporting property. A layer made of a transparent conductive film or a layer made of a transparent conductive film can be used. The device is less susceptible to problems such as energy transfer and quenching, and the range of materials to choose from is wider. It is easy to obtain a light emitting element that has both high luminous efficiency and a long life. It is easy to obtain phosphorescence in the EL layer, and also fluorescence in the EL layer. It can be used in combination with the structure.

[0133] In addition, by making the luminescent color of each EL layer different, the desired luminescent color can be obtained as a whole. For example, the color of the light emitted from the first EL layer 110a and the color of the light emitted from the second EL layer 110b can be obtained. By making the luminescent color of 110b complementary to that of 110a, the light emitting element as a whole emits white light. It is also possible to obtain a light-emitting element having three or more EL layers. The same is true.

[0134] Alternatively, as shown in FIG. 1(D), a hole injection layer 20 is provided 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 electron relay layer 207, and an EL layer 210 having a composite material layer 208 in contact with a cathode 209. may be formed.

[0135] By providing the composite material layer 208 in contact with the cathode 209, it is possible to form the cathode by using a sputtering method in particular. This is preferable because it can reduce damage to the EL layer 210 when forming the electrode. The composite material layer 208 is formed by adding an acceptor substance to the organic compound having a high hole transporting property. Composite materials containing the same may also be used.

[0136] Furthermore, by providing an electron injection buffer layer 206, the composite material layer 208 and the electron transport layer 2 Since the injection barrier between the composite material layer 208 and the electrode 205 can be reduced, the electrons generated in the composite material layer 208 can be injected into the electrode 205. The electron transport layer 205 can be easily injected.

[0137] The electron injection buffer layer 206 contains an alkali metal, an alkaline earth metal, a rare earth metal, and and their compounds (alkali metal compounds (oxides such as lithium oxide, halides, carbonates) Alkaline earth metal compounds (including carbonates such as lithium and cesium carbonate), oxides, halides compounds of rare earth metals (including oxides, halides, carbonates) or rare earth metal compounds (including oxides, halides, carbonates) It is possible to use a substance with high electron injection properties, such as tetrahydrofuran (Tetrahydrofuran) and tetrahydrofuran (Tetrahydrofuran).

[0138] The electron injection buffer layer 206 is formed by containing a substance with high electron transporting properties and a donor substance. When the compound is formed, the mass ratio to the substance having high electron transport properties is 0.001 or more and 0.1 or less It is preferable to add a donor substance in a ratio of It can be formed using the same material as that of the electron transport layer 205 described above.

[0139] In addition, the donor substance may be an alkali metal, an alkaline earth metal, a rare earth metal, or the like. These compounds (alkali metal compounds (oxides such as lithium oxide, halides, lithium carbonate, etc.) Alkaline earth metal compounds (including oxides, halides, etc.), compounds of rare earth metals (including oxides, halides, carbonates) or compounds of rare earth metals (including oxides, halides, carbonates) )), as well as tetrathianaphthacene (abbreviation: TTN), nickelocene, decamethylnickelocene, Organic compounds such as benzene can also be used.

[0140] Furthermore, an electron relay layer 207 is formed between the electron injection buffer layer 206 and the composite material layer 208. The electron relay layer 207 is not necessarily provided, but it is preferable to form the electron relay layer 207. By providing the electron relay layer 207 with high transportability, electrons can be transferred to the electron injection buffer layer 206. It will be possible to send it quickly.

[0141] The electron relay layer 207 is sandwiched between the composite material layer 208 and the electron injection buffer layer 206. The structure is composed 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 to inhibit each other's functions. Therefore, an increase in the driving voltage can be prevented.

[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 is determined by the LUMO level of the acceptor material contained in the composite material layer 208 and the electron transport The layer 204 is formed so as to be between the LUMO level of the material with high electron transporting properties contained in the layer 205 and the LUMO level of the material with high electron transporting properties.

[0143] In addition, when the electron relay layer 207 contains a donor material, the donor phase of the donor material The LUMO level of the acceptor material in the composite material layer 208 and the LUMO level of the electron transport layer 205 The LUMO level of the material with high electron transport properties is set to be between the specific energy The energy level of the material with high electron transport properties contained in the electron relay layer 207 is The MO level is set to -5.0 eV or more, preferably -5.0 eV or more and -3.0 eV or less. stomach.

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

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

[0146] The metal complexes having a metal-oxygen bond and an aromatic ligand contained in the electron relay layer 207 include: It is preferable to use a metal complex having a metal-oxygen double bond. In this case, the molecule has acceptor properties (the ability to easily accept electrons), which facilitates electron transfer (donation and receipt). In addition, metal complexes with metal-oxygen double bonds are thought to be stable. Therefore, by using a metal complex having a metal-oxygen double bond, it is possible to obtain a light-emitting device with low This makes it possible to drive the device more stably with a voltage.

[0147] As a metal complex having a metal-oxygen bond and an aromatic ligand, a phthalocyanine-based material is preferred. Specifically, VOPc (vanadyl phthalocyanine), SnO Pc(Phthalocyanine tin(IV) oxide complex) and TiOPc (Phthalocyanine titanium oxide co complex) is a molecule in which the metal-oxygen double bond acts on other molecules. This is preferred because it is easy to do and has high acceptor properties.

[0148] The above-mentioned phthalocyanine-based material preferably has a phenoxy group. Specifically, a phthalocyanine derivative having a phenoxy group, such as PhO-VOPc, is preferred. The phthalocyanine derivative having a phenoxy group is soluble in a solvent. It has the advantage of being easy to handle when forming a light-emitting element. This has the advantage that maintenance of the device used for film formation becomes easier.

[0149] The electron relay layer 207 may further contain a donor material. Alkali metals, alkaline earth metals, rare earth metals and their compounds (alkali metal compounds) (Oxides such as lithium oxide, halides, carbonates such as lithium carbonate and cesium carbonate (including oxides, halides, and carbonates), or rare earth metal compounds Compounds of metals (including oxides, halides, and carbonates), as well as tetrathianaphthacene Organic compounds such as nickelocene, decamethylnickelocene, etc. can be used. By including these donor substances in the relay layer 207, the transfer of electrons becomes easier. This makes it possible to drive the light emitting element at a lower voltage.

[0150] When the electron-relay layer 207 contains a donor substance, the above-mentioned In addition to the material, the acceptor level of the acceptor substance contained in the composite material layer 208 A substance with a high LUMO level can be used. Specific energy levels are: , and the LUMO level is in the range of -5.0 eV or more, preferably in the range of -5.0 eV or more and -3.0 eV or less. It is preferable to use a substance having a structure such as a perylene derivative. Nitrogen-containing condensed aromatic compounds are examples of such compounds. Therefore, it is a preferable material to be used for forming the electron relay layer 207. do.

[0151] Specific examples of perylene derivatives include 3,4,9,10-perylenetetracarboxylic dianhydride. (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxylic bisbenzyl Zoimidazole (abbreviation: PTCBI), N,N'-dioctyl-3,4,9,10-periodic Phenylenetetracarboxylic diimide (abbreviation: PTCDI-CH), N,N'-dihexyl- 3,4,9,10-perylenetetracarboxylic diimide (abbreviation: Hex PTC) It can be obtained.

[0152] Specific examples of nitrogen-containing condensed aromatic compounds include pyrazino[2,3-f][1,10] Phenanthroline-2,3-dicarbonitrile (PPDN), 2,3,6,7,1 0,11-Hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation :HAT(CN)6), 2,3-diphenylpyrido[2,3-b]pyrazine (abbreviation: 2P YPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (abbreviation :F2PYPR) etc.

[0153] Other examples include 7,7,8,8-tetracyanoquinodimethane (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-pentadecafluoro (fluorooctyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (abbreviation: NT CDI-C8F), 3',4'-dibutyl-5,5''-bis(dicyanomethylene)-5 ,5''-dihydro-2,2':5',2''-terthiophene) (abbreviation: DCMT), Methanofullerenes (e.g., [6,6]-phenyl C 61 butyric acid methyl ester) It is possible.

[0154] When the electron-relay layer 207 contains a donor substance, the donor substance is a substance with high electron transporting properties. The electron relay layer 207 may be formed by a method such as co-evaporation with an insulating material.

[0155] The hole injection layer 202, the hole transport layer 203, the light emitting layer 204, and the electron transport layer 205 are made of the above-mentioned materials. The EL layer 210 of this embodiment can be fabricated as described above. It is possible.

[0156] In the above-mentioned light-emitting element, a current flows due to a potential difference generated between the anode and the cathode, and the EL layer The recombination of holes and electrons at the anode or cathode generates light. Therefore, the current is taken out through either the anode or the cathode. Either one or both of them is an electrode that is transparent to visible light.

[0157] The structure of the layer provided between the anode and the cathode is not limited to the above. A region away from the anode and cathode to prevent quenching caused by the proximity of the anode and the metal Any other structure may be used as long as it has a light-emitting region where holes and electrons recombine.

[0158] That is, the layer stack structure is not particularly limited, and a material having a high electron transporting property, a material having a high hole transporting property, High electron injection material, high hole injection material, bipolar material (electron and A layer made of a material with high hole transportability or a hole blocking material can be freely combined with the light-emitting layer. It can be configured by combining them.

[0159] A passive matrix light-emitting device or a transistor light-emitting device can be manufactured by using the light-emitting element described in this embodiment mode. An active matrix light-emitting device is manufactured in which the driving of the light-emitting element is controlled by a The light-emitting device can be applied to electronic devices, lighting devices, and the like. [Example]

[0160] Example 1 In this example, a light-emitting element of one embodiment of the present invention will be described. The academic formula is shown below.

[0161] [ka]

[0162] The methods for fabricating the light-emitting element 1 and the comparative light-emitting element 2 of this example are described below.

[0163] (Light-emitting element 1) First, indium tin oxide containing silicon oxide (ITSO) was sputtered onto a glass substrate. The first electrode, which functions as an anode, was formed by a film deposition method. m, and the electrode area was 2 mm × 2 mm.

[0164] Next, as a pretreatment for forming a light emitting element on the substrate, the substrate surface was washed with water and After baking at 0°C for 1 hour, UV ozone treatment was carried out for 370 seconds.

[0165] Then, 10 -4 The substrate was placed in a heating chamber in a vacuum deposition apparatus whose interior had been decompressed to approximately 100 Pa. After vacuum baking at 170° C. for 30 minutes, the substrate was allowed to cool for about 30 minutes.

[0166] Next, the substrate is introduced into a deposition chamber in a vacuum deposition device, with the surface on which the first electrode is formed facing downward. The substrate on which the first electrode is formed is fixed to a substrate holder provided in a vacuum deposition apparatus. In this state, 10 -4 After reducing the pressure to about Pa, BPAFLP and oxidized A hole injection layer was formed by co-evaporation of molybdenum (VI). The thickness of the layer was 40 nm. The weight ratio of BPAFLP to molybdenum oxide was 4:2 (=BPAFLP:oxide). The concentration was adjusted to be molybdenum.

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

[0168] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(mppr-Me)2( dpm)] was co-evaporated to form an emitting layer on the hole transport layer. The weight ratio of Ir-II, PCBNBB and [Ir(mppr-Me)2(dpm)] was 0.8 :0.2:0.05(=2mDBTPDBq-II:PCBNBB:[Ir(mppr- The thickness of the light-emitting layer was adjusted to 40 nm.

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

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

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

[0172] Finally, a second electrode, acting as a cathode, was prepared by depositing aluminum to a thickness of 200 nm. By vapor deposition in this manner, the light-emitting element 1 of this example was fabricated.

[0173] (Comparative light-emitting element 2) The light-emitting layer of the comparative light-emitting element 2 was composed of 2mDBTPDBq-II and [Ir(mppr-Me)2 (dpm)] was co-evaporated. The weight ratio of r(mppr-Me)2(dpm) to r(mppr-Me)2(dpm) was 1:0.05 (=2mDBTPDBq -II:[Ir(mppr-Me)2(dpm)]). The thickness of the layer was 40 nm. The layers other than the light-emitting layer were fabricated in the same manner as in the light-emitting element 1.

[0174] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0175] The element structures of the light-emitting element 1 and the comparative light-emitting element 2 obtained as described above are shown in Table 1. In this study, 2mDBTPDBq-II was an n-type host, PCBNBB was a p-type host, and [Ir (mppr-Me)2(dpm)] is the guest. In contrast to the comparative light-emitting element 2, the p-type host is the emitting layer. Not present in the optic zone.

[0176] [Table 1]

[0177] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent damage, the operating characteristics of the light-emitting element were measured. The measurements were carried out at room temperature (an atmosphere maintained at 25°C).

[0178] FIG. 4 shows the current density-luminance characteristics of the light-emitting element 1 and the comparative light-emitting element 2. In FIG. is the current density (mA / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and voltage-brightness characteristics. The characteristics are shown in Figure 5. In Figure 5, the horizontal axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) The luminance-current efficiency characteristics are shown in Figure 6. In Figure 6, the horizontal axis represents luminance (cd / m 2 )of The vertical axis represents the current efficiency (cd / A). The luminance vs. external quantum efficiency characteristics are shown in Figure 7. 7, the horizontal axis is luminance (cd / m 2 ) and the vertical axis indicates the external quantum efficiency (%).

[0179] Furthermore, the luminance of the light-emitting element 1 and the comparative light-emitting element 2 was 1000 cd / m 2 Voltage when near (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A) The power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 2.

[0180] [Table 2]

[0181] Furthermore, the emission spectra when a current of 0.1 mA was applied to the light-emitting element 1 and the comparative light-emitting element 2 were , is shown in Figure 8. In Figure 8, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary unit). Also, as shown in Table 2, 1200 cd / m 2 CIE chromaticity coordinates of light-emitting element 1 at luminance of is (x,y)=(0.56,0.44), and the brightness is 960cd / m 2 Comparison of brightness at The CIE chromaticity coordinates of element 2 were (x, y) = (0.55, 0.44). The light-emitting element 1 and the comparative light-emitting element 2 are derived from [Ir(mppr-Me)2(dpm)]. It was found that orange light emission was obtained.

[0182] As can be seen from Table 2 and FIGS. 4 to 7, the light-emitting element 1 has a current The efficiency, power efficiency, and external quantum efficiency were all high. When the light is extracted to the outside, total reflection occurs between the substrate and the atmosphere, and the internal quantum efficiency It is said 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 just under 60%. It is estimated that the internal quantum efficiency of the light-emitting element 1 is increased to about 80%. From the above results, it can be seen that an element with high external quantum efficiency can be realized by applying one embodiment of the present invention. It was shown that this is possible.

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

[0185] The luminance of the comparative light-emitting element 2 after 120 hours was 58% of the initial luminance. The luminance of Light-emitting element 1 after 630 hours was 65% of the initial luminance. It was found that this element has a longer life than the comparative light-emitting element 2. It has been shown that a highly reliable element can be realized by applying one embodiment of the present invention. [Example]

[0186] Example 1 In this example, a light-emitting element of one embodiment of the present invention will be described. The chemical formula is shown below: Note that the chemical formulas of the materials used in the previous examples are omitted.

[0187] [ka]

[0188] The method for fabricating the light-emitting device 3 of this example will be described below.

[0189] (Light-emitting element 3) First, ITSO was deposited on a glass substrate by sputtering, and the first electrode, which served as an anode, was formed. The electrode was formed on the substrate. The thickness of the electrode was 110 nm, and the area of ​​the electrode was 2 mm × 2 mm. Ta.

[0190] Next, as a pretreatment for forming a light emitting element on the substrate, the substrate surface was washed with water and After baking at 0°C for 1 hour, UV ozone treatment was carried out for 370 seconds.

[0191] Then, 10 -4 The substrate is placed in a vacuum deposition apparatus whose inside pressure has been reduced to about 100 Pa. After vacuum baking at 170°C for 30 minutes in the heating chamber of the device, the substrate was left for 30 minutes. It was left to cool slightly.

[0192] Next, the substrate on which the first electrode was formed was placed in a position so that the surface on which the first electrode was formed faced downward. The substrate was fixed to a substrate holder installed in the vacuum evaporation system and -4 After reducing the pressure to about Pa, On the electrode of 1, BPAFLP and molybdenum (VI) oxide were co-deposited to form a hole injection layer. The film thickness was 40 nm, and the ratio of BPAFLP to molybdenum oxide was The ratio was adjusted to 4:2 (=BPAFLP:molybdenum oxide).

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

[0194] Furthermore, 2mDBTPDBq-II, PCBNBB, and [Ir(dppm)2(aca c)] was co-evaporated to form an emitting layer on the hole transport layer. The weight ratio of I, PCBNBB, and [Ir(dppm)2(acac)] was 0.8:0.2 :0.05(=2mDBTPDBq-II:PCBNBB:[Ir(dppm)2(ac The thickness of the light-emitting layer was adjusted to 40 nm.

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

[0196] Next, a BPhen film was formed on the first electron transport layer to a thickness of 20 nm. A transport layer was formed.

[0197] Furthermore, LiF was vapor-deposited on the second electron transport layer to a thickness of 1 nm to form an electron injection layer. .

[0198] Finally, a second electrode, acting as a cathode, was prepared by depositing aluminum to a thickness of 200 nm. By vapor deposition in this manner, the light-emitting element 3 of this example was fabricated.

[0199] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0200] The element structure of the light-emitting element 3 obtained as described above is shown in Table 3.

[0201] [Table 3]

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

[0203] The current density-luminance characteristics of the light-emitting element 3 are shown in FIG. 10. In FIG. 10, the horizontal axis represents the current density (m A / cm 2 ) and the vertical axis is luminance (cd / m 2 ) and the voltage-luminance characteristics are shown in Figure 11. In Figure 11, the horizontal axis represents voltage (V) and the vertical axis represents luminance (cd / m 2 ) and also represents The luminance-current efficiency characteristics are shown in Figure 12. In Figure 12, the horizontal axis represents the luminance (cd / m 2 ) on the vertical axis represents the current efficiency (cd / A). The luminance vs. external quantum efficiency characteristics are shown in Figure 13. In this example, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis indicates the external quantum efficiency (%).

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

[0205] [Table 4]

[0206] FIG. 14 shows the emission spectrum when a current of 0.1 mA is applied to the light-emitting element 3. In Table 14, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (arbitrary units). As shown, 1100cd / m 2 The CIE chromaticity coordinates of light-emitting element 3 at a luminance of (x, y) = (0.54, 0.46). From this result, it can be seen that the light-emitting element 3 has an It was found that orange luminescence originating from (acac)] was obtained.

[0207] As can be seen from Table 4 and FIGS. 10 to 13, the light-emitting element 3 has excellent current efficiency, power efficiency, and external The internal quantum efficiency was high, especially at 1100 cd / m 2 External quantum at the brightness of The efficiency was an extremely high 28%, which is equivalent to an internal quantum efficiency of over 90%. From the above results, it is apparent that an element with high external quantum efficiency can be realized by applying one embodiment of the present invention. It has been shown that this can be achieved.

[0208] Next, a reliability test was conducted on the light-emitting element 3. The results of the reliability test are shown in FIG. In the graph, the vertical axis shows the normalized luminance (%) when the initial luminance is 100%, and the horizontal axis shows the Indicates the operating time (h).

[0209] Reliability test: initial brightness 5000cd / m 2 The light emitting element was set at a constant current density. After 320 hours, the luminance of the light-emitting element 3 was maintained at 92% of the initial luminance. From the above results, it can be seen that a highly reliable element can be realized by applying one embodiment of the present invention. It was shown that [Example]

[0210] The T1 level of an organic material can also be determined by optical measurements of the organic material's thin film or solution. For example, to estimate the T1 level of an unknown material, In this example, Ir(dppm) used as a guest is 2acac, Ir(mppr-Me)2dpm, 2mDBT used as N-type host The T1 levels of PDBqII and PCBNBB, which are used as p-type hosts, were calculated. I put it out.

[0211] The calculation method is as follows: First, the singlet ground state (S0) and triplet ground state (S1) of each molecule are calculated. The most stable structure in the first excited state (T1) was calculated using density functional theory (DFT). Furthermore, vibration analysis was performed on the most stable structures of S0 and T1, and the zero-point corrected energy The T1 level was calculated from the difference in the zero-point corrected energy between S0 and T1.

[0212] In the calculations of N-type and P-type host molecules, the basis functions for all atoms are 6-3 11G (triple split v using three contraction functions for each valence orbital) The basis functions of the above-mentioned basis set are used. For example, the H atom For a C atom, the orbitals 1s to 3s are considered, and for a C atom, the orbitals 1s to 4s and 2p to 4p are considered. Furthermore, to improve the accuracy of the calculation, the H atom is used as a polarization basis set. p-function was added to atoms, and d-function was added to atoms other than H atoms. The weight of each parameter related to the correlation energy was defined.

[0213] In the calculation of the guest molecule, LanL2DZ was used as the basis function for the Ir atom. The basis set used was 6-311G. Furthermore, to improve the accuracy of the calculation, the polarization basis set was The p function was added to H atoms, and the d function was added to atoms other than H atoms. The functional used was B3PW91. The weights of the parameters related to the exchange and correlation energies were defined.

[0214] The quantum chemistry calculation program used was Gaussian09. The experiment was carried out using a high-performance computer (SGI, Altix4700). .

[0215] The calculated T1 level is 2.13 eV for Ir(dppm)2acac, Ir(mppr-Me)2dpm is 2.13 electron volts, 2mDBTPDBqII is 2. 42 eV and PCBNBB 2.31 eV. These values ​​were obtained by optical measurements. It was close to what was obtained in

[0216] From the above results, it is clear that 2mDBTPDBqII, which is used as an N-type host, and P-type host The T1 level of PCBNBB used as a guest is )2acac, which is 0.15 eV higher than the T1 level of Ir(mppr-Me)2dpm Therefore, it was found that the triplet excited state of the guest molecule can be converted into an N-type host molecule or a P-type The transition of the host molecule to the triplet excited state can be sufficiently prevented, resulting in high external quantum efficiency. It was suggested that a light-emitting device could be obtained.

[0217] Thus, the T1 level obtained by optical measurement and the T1 level obtained by molecular orbital calculation are very different. Therefore, molecular orbital calculations can be performed without synthesizing new organic compounds. It is useful to evaluate the T1 level of the organic compound and improve the luminescence efficiency of the organic compound. It can be determined whether or not [Explanation of symbols]

[0218] 101 Substrate 102 Light-emitting layer 103 First electrode 104 Second electrode 105 First carrier injection layer 106 First carrier 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 Light-emitting layer 205 Electron transport layer 206 Electron injection buffer layer 207 Electronic Relay Layer 208 Composite material layer 209 Cathode 210 EL layer

Claims

1. an anode, a cathode, a hole injection layer between the anode and the cathode, and a light-emitting layer; the light-emitting layer includes a phosphorescent compound, a first organic compound having an electron transport property, and a second organic compound having a hole transport property; The hole injection layer comprises two materials: one of the two materials is an aromatic amine compound or a carbazole derivative; the first organic compound and the second organic compound are a combination that forms an exciplex, an emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of the phosphorescent compound; an energy difference between the triplet excited state and the ground state of the first organic compound is greater than an energy difference between the triplet excited state and the ground state of the phosphorescent compound by 0.15 eV or more; A light-emitting element, wherein the energy difference between the triplet excited state and the ground state of the second organic compound is 0.15 eV or more larger than the energy difference between the triplet excited state and the ground state of the phosphorescent compound.

2. an anode, a cathode, a hole injection layer between the anode and the cathode, and a light-emitting layer; the light-emitting layer includes a phosphorescent compound, a first organic compound having an electron transport property, and a second organic compound having a hole transport property; The hole injection layer comprises two materials: one of the two materials is an aromatic amine compound or a carbazole derivative; the other of the two materials is a fluorine-containing organic compound, the first organic compound and the second organic compound are a combination that forms an exciplex, an emission spectrum of the exciplex overlaps with an absorption band located at the longest wavelength side of the phosphorescent compound; an energy difference between the triplet excited state and the ground state of the first organic compound is greater than an energy difference between the triplet excited state and the ground state of the phosphorescent compound by 0.15 eV or more; A light-emitting element, wherein the energy difference between the triplet excited state and the ground state of the second organic compound is 0.15 eV or more larger than the energy difference between the triplet excited state and the ground state of the phosphorescent compound.

3. In claim 1 or claim 2, The molar absorption coefficient of the absorption band located on the longest wavelength side of the phosphorescent compound is 2000 M －１ ・cm －１ The light-emitting element is as described above.

4. In any one of claims 1 to 3, The phosphorescent compound is an organometallic complex.

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

Images