Light-emitting element

Abstract

Provided is a light-emitting element having high external quantum efficiency. The invention provides a light-emitting element with a long service life. Provided is a light-emitting element including a light-emitting layer including a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, in which a combination of the first organic compound and the second organic compound forms an exciplex. The light-emitting element transfers energy by using the overlap between the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound, and thus has high energy transfer efficiency. Consequently, a light-emitting element having high external quantum efficiency can be realized.

Description

[0001] This application is a divisional application filed in response to divisional application 202310224426.4. Divisional application 202310224426.4 is a divisional application of the invention patent application filed on February 6, 2012, with application number "201280002425.5" and title "Light Emitting Element". Technical Field

[0002] This invention relates to a light-emitting element that utilizes the organic electroluminescence (EL) phenomenon (hereinafter also referred to as an organic EL element). Background Technology

[0003] Research and development of organic EL (Elastic Optical Cell) elements are actively underway. The basic structure of an organic EL element consists of a layer containing a luminescent organic compound (hereinafter also referred to as the emissive layer) sandwiched between a pair of electrodes. Organic EL elements are attracting attention as next-generation flat panel display elements due to their advantages such as thin and lightweight design, high-speed response to input signals, and low-voltage DC drive capability. Furthermore, displays using this type of emissive element exhibit excellent contrast and image quality, as well as wide viewing angles. Moreover, since organic EL elements are surface light sources, their application in applications such as backlights for liquid crystal displays and lighting devices is anticipated.

[0004] The light-emitting mechanism of organic EL devices is carrier injection type. In other words, by applying a voltage between electrodes sandwiching the light-emitting layer, electrons and holes injected from the electrodes recombine, exciting the light-emitting material. When this excited state returns to the ground state, light is emitted. There are two types of excited states: singlet excited state (S... * ) and triple excited state (T * In light-emitting elements, the statistically significant ratio of singlet excited states to triplet excited states is considered to be S0. * :T * =1:3.

[0005] The ground state of luminescent organic compounds is typically a singlet excited state. Therefore, compounds originating from the singlet excited state (S... * The luminescence of electrons from the triplet excited state (T0) is called fluorescence because it occurs during electronic transitions between the same spin multiplicity. On the other hand, fluorescence originates from the triplet excited state (T0). * The luminescence of phosphorescence is caused by electronic transitions between different spin multiplicity states. However, in compounds that emit fluorescence (hereinafter referred to as fluorescent compounds), phosphorescence is typically not observed at room temperature; only fluorescence is observed. Therefore, based on S... * :T *=1:3, the theoretical limit of the internal quantum efficiency (the ratio of generated photons to injected charge carriers) in a light-emitting element using fluorescent compounds is considered to be 25%.

[0006] On the other hand, if phosphorescent compounds (hereinafter referred to as phosphorescent compounds) are used, the internal quantum efficiency can theoretically reach 100%. In other words, higher luminous efficiency can be obtained compared to using fluorescent compounds. Based on the above reasons, in order to achieve high-efficiency light-emitting elements, light-emitting elements using phosphorescent compounds have been actively developed in recent years. In particular, organometallic complexes with iridium or similar central metals have attracted attention as phosphorescent compounds due to their high phosphorescence quantum yield. For example, Patent Document 1 discloses an organometallic complex with iridium as a central metal as a phosphorescent material.

[0007] When the phosphorescent compound described above is used to form the luminescent layer of a light-emitting element, in order to suppress concentration quenching of the phosphorescent compound or quenching caused by triplet-triplet annihilation, the luminescent layer is usually formed by dispersing the phosphorescent compound in a matrix of another compound. Here, the compound used as the matrix is ​​called the host material, and the compound dispersed in the matrix, such as the phosphorescent compound, is called the guest material.

[0008] [References]

[0009] [Patent Literature]

[0010] [Patent Document 1] International Publication No. 00 / 70655 Summary of the Invention

[0011] However, the light extraction efficiency of organic EL elements is generally considered to be around 20% to 30%. Therefore, when considering the absorption of light by the reflective and transparent electrodes, the limit of the external quantum efficiency of light-emitting elements using phosphorescent compounds is at most about 25%.

[0012] One objective of one aspect of the present invention is to provide a light-emitting element with high external quantum efficiency. Another objective of one aspect of the present invention is to provide a light-emitting element with long lifetime.

[0013] One aspect of the present invention is a light-emitting element comprising: a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, wherein the combination of the first organic compound and the second organic compound forms an excimer complex.

[0014] Another aspect of the present invention is a light-emitting element comprising: a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, wherein the combination of the first organic compound and the second organic compound forms an excimer complex, and the excimer complex acts on the phosphorescent compound to cause the phosphorescent compound to emit phosphorescence.

[0015] Another aspect of the present invention is a light-emitting element comprising: a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, wherein the singlet excitons of the first organic compound form an excitocomplex.

[0016] Another aspect of the present invention is a light-emitting element comprising: a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, wherein the anions of the first organic compound and the cations of the second organic compound form an excitocomplex.

[0017] In the above-mentioned light-emitting element, the excitation energy of the excitocomplex is preferably transferred to the phosphorescent compound to make the phosphorescent compound emit phosphorescence.

[0018] In the above-mentioned light-emitting element, at least one of the first organic compound and the second organic compound is preferably a fluorescent compound.

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

[0020] The light-emitting element of one aspect of the present invention can be applied to light-emitting devices, electronic devices, and lighting devices.

[0021] One aspect of the present invention can provide a light-emitting element with high external quantum efficiency. Another aspect of the present invention can provide a light-emitting element with long lifetime. Attached Figure Description

[0022] Figure 1A and Figure 1B This is a graph showing the absorption and emission spectra of Example 1;

[0023] Figure 2A and Figure 2B This is a graph showing the absorption and emission spectra of Example 2;

[0024] Figure 3 This is a graph showing the current density-brightness characteristics of the light-emitting element in Example 3;

[0025] Figure 4 This is a graph showing the voltage-brightness characteristics of the light-emitting element in Embodiment 3;

[0026] Figure 5This is a graph showing the brightness-current efficiency characteristics of the light-emitting element in Embodiment 3;

[0027] Figure 6 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element in Example 3;

[0028] Figure 7 This is a graph showing the emission spectrum of the light-emitting element in Example 3;

[0029] Figure 8 This is a graph showing the results of a reliability test of the light-emitting element in Example 3;

[0030] Figure 9 This is a graph showing the current density-brightness characteristics of the light-emitting element in Example 4;

[0031] Figure 10 This is a graph showing the voltage-brightness characteristics of the light-emitting element in Embodiment 4;

[0032] Figure 11 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element in Embodiment 4;

[0033] Figure 12 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element in Example 4;

[0034] Figure 13 This is a graph showing the emission spectrum of the light-emitting element in Example 4;

[0035] Figure 14 This is a graph showing the results of a reliability test of the light-emitting element in Example 4;

[0036] Figure 15 This is a diagram illustrating the structure of the light-emitting element in the embodiment;

[0037] Figures 16A to 16C This is a diagram illustrating a light-emitting element according to one aspect of the present invention;

[0038] Figure 17 This is a diagram showing the energy levels of the excimer complex used in one aspect of the invention;

[0039] Figure 18A and Figure 18B This is a graph showing the absorption and emission spectra of Example 5;

[0040] Figure 19 This is a graph showing the current density-brightness characteristics of the light-emitting element in Example 6;

[0041] Figure 20 This is a graph showing the voltage-brightness characteristics of the light-emitting element in Embodiment 6;

[0042] Figure 21 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element in Embodiment 6;

[0043] Figure 22 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element of Example 6;

[0044] Figure 23 This is a graph showing the emission spectrum of the light-emitting element of Example 6;

[0045] Figure 24 This is a graph showing the results of a reliability test of the light-emitting element in Example 6;

[0046] Figure 25 This is a diagram illustrating the concept of one aspect of the present invention;

[0047] Figure 26A and Figure 26B This is a graph showing the absorption and emission spectra of Example 7;

[0048] Figure 27 This is a graph showing the current density-brightness characteristics of the light-emitting element in Example 8;

[0049] Figure 28 This is a graph showing the voltage-brightness characteristics of the light-emitting element in Embodiment 8;

[0050] Figure 29 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element in Embodiment 8;

[0051] Figure 30 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element in Example 8;

[0052] Figure 31 This is a graph showing the emission spectrum of the light-emitting element of Example 8;

[0053] Figure 32A and Figure 32B This is a graph showing the absorption and emission spectra of Example 9;

[0054] Figure 33 This is a graph showing the current density-brightness characteristics of the light-emitting element of Embodiment 10;

[0055] Figure 34 This is a graph showing the voltage-brightness characteristics of the light-emitting element of Embodiment 10;

[0056] Figure 35 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element of Embodiment 10;

[0057] Figure 36This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element of Example 10;

[0058] Figure 37 This is a graph showing the emission spectrum of the light-emitting element of Example 10;

[0059] Figure 38 This is a graph showing the results of a reliability test of the light-emitting element of Example 10;

[0060] Figure 39A and Figure 39B This is a graph showing the absorption and emission spectra of Example 11;

[0061] Figure 40 This is a graph showing the current density-brightness characteristics of the light-emitting element in Embodiment 12;

[0062] Figure 41 This is a graph showing the voltage-brightness characteristics of the light-emitting element of Embodiment 12;

[0063] Figure 42 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element of Embodiment 12;

[0064] Figure 43 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element of Example 12;

[0065] Figure 44 This is a graph showing the emission spectrum of the light-emitting element of Example 12;

[0066] Figure 45 This is a graph showing the results of a reliability test of the light-emitting element in Example 12;

[0067] Figure 46A and Figure 46B This is a graph showing the absorption and emission spectra of Example 13;

[0068] Figure 47 This is a graph showing the current density-brightness characteristics of the light-emitting element in Embodiment 14;

[0069] Figure 48 This is a graph showing the voltage-brightness characteristics of the light-emitting element of Embodiment 14;

[0070] Figure 49 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element of Embodiment 14;

[0071] Figure 50 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element of Embodiment 14;

[0072] Figure 51This is a graph showing the emission spectrum of the light-emitting element of Example 14;

[0073] Figure 52A and Figure 52B This is a graph showing the absorption and emission spectra of Example 15;

[0074] Figure 53 This is a graph showing the current density-brightness characteristics of the light-emitting element of Embodiment 16;

[0075] Figure 54 This is a graph showing the voltage-brightness characteristics of the light-emitting element of Embodiment 16;

[0076] Figure 55 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element of Embodiment 16;

[0077] Figure 56 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element of Embodiment 16;

[0078] Figure 57 This is a graph showing the emission spectrum of the light-emitting element of Embodiment 16;

[0079] Figure 58A and Figure 58B This is a graph showing the absorption and emission spectra of Example 17;

[0080] Figure 59 This is a graph showing the current density-brightness characteristics of the light-emitting element of Embodiment 18;

[0081] Figure 60 This is a graph showing the voltage-brightness characteristics of the light-emitting element of Embodiment 18;

[0082] Figure 61 This is a graph showing the brightness-current efficiency characteristics of the light-emitting element of Embodiment 18;

[0083] Figure 62 This is a graph showing the brightness-external quantum efficiency characteristics of the light-emitting element of Embodiment 18;

[0084] Figure 63 This is a graph showing the emission spectrum of the light-emitting element of Example 18.

[0085] Figure 64 This is a diagram illustrating the calculation results related to one aspect of the present invention;

[0086] Figure 65A1 , Figure 65A2 , Figure 65B1 , Figure 65B2 , Figure 65C1 , Figure 65C2This is a diagram showing the calculation results related to one aspect of the present invention. Detailed Implementation

[0087] The embodiments will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following description, and those skilled in the art will readily understand that the invention can be modified in various forms without departing from its spirit and scope. Therefore, the present invention should not be construed as being limited only to the contents described in the embodiments shown below. Note that in the inventive structures described below, the same reference numerals are used in different drawings to denote the same parts or parts having the same function, and repeated descriptions are omitted.

[0088] (Implementation Method 1)

[0089] This embodiment describes a light-emitting element according to one aspect of the present invention.

[0090] The light-emitting element of this embodiment includes a light-emitting layer, which has a guest material as a light-emitting substance, a first organic compound, and a second organic compound. Specifically, a phosphorescent compound is used as the guest material. Furthermore, in this specification, the material contained in the light-emitting layer in greater quantity among the first and second organic compounds is referred to as the host material.

[0091] By employing a structure in which the guest material is dispersed within the host material, crystallization of the light-emitting layer can be suppressed. Furthermore, by suppressing concentration quenching caused by high concentrations of the guest material, the luminous efficiency of the light-emitting element can be improved.

[0092] Furthermore, in this embodiment, the triplet excited state energy (T1 level) of each of the first organic compound and the second organic compound is preferably higher than the T1 level of the guest material. This is because if the T1 level of the first organic compound (or the second organic compound) is lower than the T1 level of the guest material, the first organic compound (or the second organic compound) quenches the triplet excited state energy of the guest material that contributes to luminescence, resulting in a decrease in luminescence efficiency.

[0093] <Basic Process of Light Emission>

[0094] First, the general basic process of luminescence in a light-emitting element that uses phosphorescent compounds as guest materials will be explained.

[0095] (1) When electrons and holes recombine in a guest molecule, the guest molecule is in an excited state (direct recombination process).

[0096] (1-1) When the excited state of the guest molecule is a triplet excited state, the guest molecule emits phosphorescence.

[0097] (1-2) When the excited state of the guest molecule is a singlet excited state, the guest molecule in the singlet excited state intersystem crosses to the triplet excited state and emits phosphorescence.

[0098] In other words, in the direct recombination process described in (1) above, high luminescence efficiency can be obtained as long as the intersystem crossing efficiency and phosphorescence quantum yield of the guest molecule are high. Furthermore, as mentioned above, the T1 energy level of the host molecule is preferably higher than that of the guest molecule.

[0099] (2) When electrons and holes recombine in the main molecule, the main molecule is in an excited state (energy transfer process).

[0100] (2-1) When the excited state of the host molecule is a triplet excited state, and the T1 energy level of the host molecule is higher than that of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule, and the guest molecule is in a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. In addition, theoretically, it is possible for energy to be transferred to the singlet excited level (S1 level) of the guest molecule, but in many cases the S1 level of the guest molecule has a higher energy than the T1 level of the host molecule, and it is not likely to become the main energy transfer process, so it is omitted here.

[0101] (2-2) When the excited state of the host molecule is a singlet excited state, and the S1 energy level of the host molecule is higher than the S1 and T1 energy levels of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule. Therefore, the guest molecule is in a singlet excited state or a triplet excited state. Guest molecules in a triplet excited state emit phosphorescence. In addition, guest molecules in a singlet excited state can also emit phosphorescence by transitioning to a triplet excited state.

[0102] In other words, in the energy transfer process described in (2) above, it is important to transfer the triple excitation energy and single excitation energy of the host molecule to the guest molecule as efficiently as possible.

[0103] Given the energy transfer process described above, if the host molecule itself deactivates by releasing the excitation energy as light or heat before it is transferred from the host molecule to the guest molecule, the luminescence efficiency decreases. Here, the inventors have discovered that when the host molecule is in a singlet excited state (as described in (2-2) above), compared to when it is in a triplet excited state (as described in (2-1) above), energy is less readily transferred to the guest molecule of the phosphorescent compound, making the luminescence efficiency more prone to decrease. This has become a research objective of the inventors. The reasons for this can be found in the energy transfer process described in more detail below.

[0104] <Energy Transfer Process>

[0105] The following section details the energy transfer process between molecules.

[0106] First, two mechanisms are proposed as intermolecular energy transfer mechanisms. Here, the molecule that imparts excitation energy is denoted as the host molecule, and the molecule that receives excitation energy is denoted as the guest molecule.

[0107] The Förster Mechanism (Dipole-Dipole Interactions)

[0108] In the Förster mechanism (also known as Förster resonance energy transfer), energy transfer does not require direct intermolecular contact. Energy transfer occurs through the resonance of dipole oscillations between the host and guest molecules. Through this resonance, the host molecule supplies energy to the guest molecule, which is in its ground state while the guest molecule is in its excited state. Equation (1) shows the rate constant of the Förster mechanism. .

[0109] [Formula 1]

[0110]

[0111] In formula (1), Indicates frequency, The normalized emission spectrum of the main molecule (fluorescence spectrum of singlet excited state energy transfer, phosphorescence spectrum of triplet excited state energy transfer). The molar absorptivity of the guest molecule is given by: N (Avogadro number), n (refractive index of the medium), R (intermolecular distance between the host and guest molecules), τ (lifetime of the excited state being measured, fluorescence lifetime or phosphorescence lifetime), c (speed of light), φ (luminescence quantum yield, fluorescence quantum yield of singlet excited state energy transfer, phosphorescence quantum yield of triplet excited state energy transfer), and K (light emission quantum yield). 2 The coefficients (0 to 4) represent the orientation of the transition dipole moments of the host and guest molecules. Furthermore, in random orientations, K... 2 =2 / 3.

[0112] The Dexter Mechanism (Electron Exchange Interaction)

[0113] In the Dexter mechanism (also known as Dexter electron transfer), the host molecule and the guest molecule approach the effective contact distance for orbital overlap, and the excited-state host molecule and the ground-state guest molecule exchange electrons, resulting in energy transfer. Equation 2 shows the rate constant of the Dexter mechanism. .

[0114] [Formula 2]

[0115]

[0116] In formula (2), h represents Planck's constant, and K represents a constant with energy dimension. Indicates frequency, The normalized emission spectrum of the main molecule (fluorescence spectrum from energy transfer of singlet excited state, phosphorescence spectrum from energy transfer of triplet excited state). The normalized absorption spectrum of the guest molecule is represented by L, where L represents the effective molecular radius and R represents the intermolecular distance between the host molecule and the guest molecule.

[0117] Here, we can consider the energy transfer efficiency from the host molecule to the guest molecule as expressed by formula (3). In the formula, k r The rate constant k represents the luminescence process of the host molecule (fluorescence from the energy transfer of the singlet excited state, and phosphorescence from the energy transfer of the triplet excited state). n The rate constant represents the non-luminescent process (thermal deactivation or intersystem crossing) of the host molecule, and τ represents the lifetime of the excited state of the host molecule detected.

[0118] [Formula 3]

[0119]

[0120] First, as can be seen from formula (3), in order to improve energy transfer efficiency... The rate constant of energy transfer The velocity constant k competing with others r +k n (=1 / τ) can be further increased. Furthermore, to increase the rate constant of this energy transfer... As can be seen from formulas (1) and (2), in the Foster mechanism and the Dexter mechanism, the preferred emission spectrum of the host molecule (fluorescence spectrum from energy transfer of singlet excited state, phosphorescence spectrum from energy transfer of triplet excited state) overlaps with the absorption spectrum of the guest molecule.

[0121] Here, the inventors believe that, taking into account the overlap between the emission spectrum of the host molecule and the absorption spectrum of the guest molecule, the absorption band on the side of the longest wavelength (low energy) in the absorption spectrum of the guest molecule is important.

[0122] In this embodiment, a phosphorescent compound is used as the guest material. In the absorption spectrum of the phosphorescent compound, the absorption band that is considered to contribute most to luminescence is located at or near the absorption wavelength corresponding to the direct transition from the singlet ground state to the triplet excited state; this is the absorption band appearing on the longest wavelength side. Therefore, it is considered preferable that the emission spectrum (fluorescence spectrum and phosphorescence spectrum) of the host material overlaps with the absorption band on the longest wavelength side of the phosphorescent compound's absorption spectrum.

[0123] For example, most organometallic complexes, especially luminescent iridium complexes, exhibit a broad absorption band on the longest wavelength side around 500 nm to 600 nm (of course, depending on the emission wavelength, the broad absorption band can appear on either the shorter or longer wavelength side). This absorption band primarily originates from triplet MLCT (metal-to-ligand charge transfer) transitions. However, it can be considered that this absorption band also includes those originating from triplet states. The absorption of transitions and singlet MLCT transitions overlaps with each other, forming a broad absorption band on the longest wavelength side of the absorption spectrum. In other words, the difference between the lowest singlet excited state and the lowest triplet excited state is small, and the absorptions of these excited states overlap, forming a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, when organometallic complexes (especially iridium complexes) are used as guest materials, it is preferable, as described above, that the broad absorption band on the longest wavelength side overlaps more with the emission spectrum of the host material.

[0124] Here, firstly, energy transfer from the triplet excited state of the host material is considered. As explained above, in energy transfer from the triplet excited state, it is preferable that the phosphorescence spectrum of the host material and the absorption band of the longest wavelength side of the guest material overlap more significantly.

[0125] Furthermore, generally speaking, because fluorescent compounds are used as the host material, the phosphorescence lifetime (τ) is very long, exceeding milliseconds (k). r +k n (Small). This is because the transition from the triplet excited state to the ground state (singlet) is a forbidden transition. As can be seen from formula (3), this is beneficial to energy transfer efficiency. This also means that energy transfer from the triplet excited state of the host material to the triplet excited state of the guest material is likely to occur.

[0126] However, the problem here lies in energy transfer from the singlet excited state of the host material. To efficiently transfer energy from the singlet excited state in addition to energy transfer from the triplet excited state, as explained above, it is necessary to design the fluorescence spectrum to overlap with the absorption band of the longest wavelength side of the guest material, in addition to the phosphorescence spectrum of the host material. In other words, if the host material is not designed so that its fluorescence spectrum is located approximately at the same position as its phosphorescence spectrum, efficient energy transfer from both the singlet and triplet excited states of the host material is not possible.

[0127] However, generally speaking, since the S1 energy level is significantly different from the T1 energy level (S1 energy level > T1 energy level), the emission wavelengths of fluorescence and phosphorescence are also significantly different (fluorescence emission wavelength < phosphorescence emission wavelength). For example, in light-emitting elements using phosphorescent compounds, 4,4'-bis(N-carbazolyl)biphenyl (abbreviation: CBP), typically used as the host material, has a phosphorescence spectrum around 500 nm and a fluorescence spectrum around 400 nm, with a 100 nm gap between the two. From the above example, it is extremely difficult to design a host material with its fluorescence spectrum located approximately at the same position as its phosphorescence spectrum. Therefore, the inventors believe that improving the energy transfer efficiency from the singlet excited state of the host material to the guest material is an important research topic.

[0128] Furthermore, the fluorescence lifetime (τ) of the fluorescent compound used as the host material is extremely short, on the order of nanoseconds (k). r +k n (Large). This is because the transition from the singlet excited state to the ground state (singlet) is an allowed transition. As can be seen from formula (3), this is detrimental to energy transfer efficiency. This also means that energy transfer from the singlet excited state of the host material to the guest material is not easy.

[0129] One aspect of the present invention is a useful method that can overcome the problem of energy transfer efficiency from a singlet excited state of the host material to the guest material.

[0130] Furthermore, since phosphorescent compounds can convert both singlet and triplet excited states into light emission by utilizing intersystem crossing (refer to "(1) direct recombination process" above), the internal quantum efficiency of light-emitting elements using phosphorescent compounds can theoretically reach 100%. Moreover, it has been discussed that, assuming a light extraction efficiency of 20%, a light-emitting element with an external quantum efficiency of 20% can achieve an internal quantum efficiency of almost 100%. However, it can be considered that, since the energy transfer from the singlet excited state of the host material was not considered, the internal quantum efficiency of 100% has not actually been achieved in these existing light-emitting elements. This is because, by implementing one aspect of the present invention described below, the inventors have achieved an external quantum efficiency of 30%. In other words, an external quantum efficiency of at least 30% is equivalent to an internal quantum efficiency of 100%, and one aspect of the present invention is a useful method for achieving this. Note that it can be estimated from this that the existing external quantum efficiency of 20% is equivalent to an internal quantum efficiency of less than or equal to 70%.

[0131] <One aspect of the invention>

[0132] One aspect of the present invention is a light-emitting element comprising: a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, wherein the combination of the first organic compound and the second organic compound forms an excimer complex.

[0133] The first and second organic compounds form an exciplex through carrier recombination (or singlet excitons). When the formed exciplex emits light, its emission wavelength is on the longer wavelength side relative to each emission wavelength (fluorescence wavelength) of the first and second organic compounds. In other words, by forming the exciplex, the fluorescence spectrum of the first or second organic compound can be transformed into an emission spectrum on the longer wavelength side.

[0134] Therefore, as Figure 25 As shown, even if the fluorescence spectrum of the first organic compound (or the second organic compound) is located on the shorter wavelength side compared to the absorption band on the longest wavelength side of the phosphorescent compound, and does not overlap with that absorption band, a longer wavelength emission spectrum can be obtained by forming an excimer complex, thereby increasing the overlap with that absorption band. The light-emitting element of one aspect of the present invention achieves high energy transfer efficiency because it utilizes the overlap between the emission spectrum of the excimer complex and the absorption spectrum of the phosphorescent compound for energy transfer. Therefore, one aspect of the present invention can realize a light-emitting element with high external quantum efficiency.

[0135] Furthermore, since the excitocomplex exists only in the excited state, it lacks a ground state that absorbs energy. Therefore, it can be assumed that, in principle, the energy of the singlet and triplet excited states of the phosphorescent compound does not transfer back to the excitocomplex, and the phosphorescent compound does not become inactive before luminescence (i.e., its luminescence efficiency decreases). This also contributes to improving the external quantum efficiency.

[0136] Furthermore, the difference between the singlet and triplet excitation energies of the excimer complex is considered to be minimal. In other words, the emission spectrum of the singlet state of the excimer complex is extremely close to that of its triplet excited state. Therefore, as described above, when the emission spectrum of the excimer complex (generally considered to be the singlet state emission spectrum) is designed to overlap with the absorption band on the longest wavelength side of the phosphorescent compound, the emission spectrum of the triplet state of the excimer complex (not observable at room temperature, and in many cases not observable at low temperatures) also overlaps with the absorption band on the longest wavelength side of the phosphorescent compound. More specifically, this means that energy can be efficiently transferred from both the singlet and triplet states of the excimer complex to the phosphorescent compound.

[0137] To examine whether excimer complexes actually possess the aforementioned properties, molecular orbital calculations are used. Generally, the combination of heteroaromatic compounds and aromatic amines is often influenced by the LUMO levels of heteroaromatic compounds (which are deeper than the lowest unoccupied molecular orbital (LUMO) level of aromatic amines, indicating a greater tendency to accept electrons) and the HOMO levels of aromatic amines (which are shallower than the highest occupied molecular orbital (HOMO) level of heteroaromatic compounds, indicating a greater tendency to accept holes), thus forming excimer complexes. Therefore, calculations are performed using the combination of dibenzo[f,h]quinoxaline (abbreviation: DBq), which forms the typical LUMO skeleton of heteroaromatic compounds, and triphenylamine (abbreviation: TPA), which forms the typical HOMO skeleton of aromatic amines.

[0138] First, the optimal molecular structures and excitation energies in the lowest excited singlet (S1) and lowest excited triplet (T1) states of the DBq and TPA monomers were calculated using time-dependent density functional theory (TD-DFT). Then, the excitation energies of the DBq and TPA dimers were calculated. The total energy of the DFT is expressed as the sum of the potential energy, electrostatic energy between electrons, kinetic energy of electrons, and exchange-correlation energies including all other complex inter-electron interactions. In the DFT, the exchange-correlation interaction is approximated by a functional of the single-electron potential expressed in terms of electron density, resulting in fast calculations and high accuracy. Here, the weights of the parameters involving the exchange-correlation energies are specified using B3LYP as a mixed functional. Furthermore, a 6-311 basis function (a triple splitvalence basis function using three shortened functions for each atomic valence orbital) is applied to all atoms as a basis function. The aforementioned basis functions, for example, consider the 1s to 3s orbitals for hydrogen atoms, and the 1s to 4s and 2p to 4p orbitals for carbon atoms. Furthermore, to improve computational accuracy, p functions are added for hydrogen atoms as polarization basis classes, and d functions are added for atoms other than hydrogen atoms.

[0139] Furthermore, Gaussian09 was used as the quantum chemistry calculation program. The calculations were performed using a high-performance computer (SGI Altix 4700, manufactured by SGI Corporation).

[0140] First, the HOMO and LUMO energy levels were calculated for DBq monomers, TPA monomers, and the dimer of DBq and TPA. Figure 64 The HOMO and LUMO energy levels are shown, and Figures 65(A1), 65(A2), 65(B1), 65(B2), 65(C1) and 65(C2) show the distribution of HOMO and LUMO.

[0141] Figure 65(A1) shows the LUMO distribution of DBq monomer, Figure 65(A2) shows the HOMO distribution of DBq monomer, Figure 65(B1) shows the LUMO distribution of TPA monomer, Figure 65(B2) shows the HOMO distribution of TPA monomer, Figure 65(C1) shows the LUMO distribution of the dimer of DBq and TPA, and Figure 65(C2) shows the HOMO distribution of the dimer of DBq and TPA.

[0142] like Figure 64As shown, the dimer of DBq and TPA is influenced by the LUMO level of DBq (-1.99 eV), which is deeper (lower) than the LUMO level of TPA, and the HOMO level of TPA (-5.21 eV), which is shallower (higher) than the HOMO level of DBq, thus forming an excitosome complex of DBq and TPA. In fact, as can be seen from Figures 65(C1) and 65(C2), the LUMO of the DBq and TPA dimer is distributed on the DBq side, while the HOMO is distributed on the TPA side.

[0143] Next, the excitation energies obtained from the optimal molecular structures of DBq monomers S1 and T1 are shown. Here, the excitation energies of S1 and T1 correspond to the wavelengths of fluorescence and phosphorescence emitted by the DBq monomer, respectively. The excitation energy of S1 of the DBq monomer is 3.294 eV, and the fluorescence wavelength is 376.4 nm. Furthermore, the excitation energy of T1 of the DBq monomer is 2.460 eV, and the phosphorescence wavelength is 504.1 nm.

[0144] Furthermore, the excitation energies obtained from the optimal molecular structures of TPA monomers S1 and T1 are shown. Here, the excitation energies of S1 and T1 correspond to the wavelengths of fluorescence and phosphorescence emitted by the TPA monomer, respectively. The excitation energy of S1 for TPA monomer is 3.508 eV, and the fluorescence wavelength is 353.4 nm. Additionally, the excitation energy of T1 for TPA monomer is 2.610 eV, and the phosphorescence wavelength is 474.7 nm.

[0145] Furthermore, the excitation energies obtained from the optimal molecular structures of the S1 and T1 dimers of DBq and TPA are shown. The excitation energies of S1 and T1 correspond to the wavelengths of fluorescence and phosphorescence emitted by the DBq and TPA dimers, respectively. The excitation energy of S1 for the DBq and TPA dimer is 2.036 eV, and the fluorescence wavelength is 609.1 nm. Additionally, the excitation energy of T1 for the DBq and TPA dimer is 2.030 eV, and the phosphorescence wavelength is 610.0 nm.

[0146] As described above, the phosphorescence wavelength of either the DBq monomer or the TPA monomer shifts to a longer wavelength by approximately 100 nm compared to the fluorescence wavelength. This result shows the same tendency as the CBP (actual measurement) mentioned above, supporting the validity of the calculation.

[0147] On the other hand, the fluorescence wavelength of the DBq and TPA dimer is on the longer wavelength side compared to the fluorescence wavelength of either the DBq monomer or the TPA monomer. This result shows that the examples described later (actual measurements) also exhibit the same tendency, supporting the validity of the calculations. Furthermore, the difference between the fluorescence and phosphorescence wavelengths of the DBq and TPA dimer is only 0.9 nm, and they are almost equal in wavelength.

[0148] The results above indicate that the excitocomplex can integrate singlet and triplet excited state energies into approximately the same level. Therefore, as mentioned above, the excitocomplex can efficiently transfer energy from both singlet and triplet excited states to the phosphorescent compound.

[0149] This effect is achieved by using the excimer complex as the medium for energy transfer. Generally, this considers energy transfer from a singlet or triplet excited state of the host material to the phosphorescent compound. However, a significant difference between this invention and the prior art lies in the fact that an excimer complex (an excimer complex of a first organic compound and a second organic compound) is first formed from the host material and other materials, and energy transfer is then performed using this excimer complex. Furthermore, this difference allows for higher luminescence efficiency than previously possible.

[0150] Furthermore, generally speaking, when excimer compounds are used in the luminescent layer of a light-emitting element, the emission color can be suppressed, but the luminous efficiency is usually significantly reduced. Therefore, it has been conventionally considered unsuitable to use excimer compounds to obtain high-efficiency light-emitting elements. However, as shown in one aspect of the present invention, the inventors have discovered that by using excimer compounds in the medium for energy transfer from phosphorescent compounds, the luminous efficiency can be increased to its limit. This is a technical concept contrary to existing fixed ideas.

[0151] To ensure sufficient overlap between the emission spectrum of the excimer complex and the absorption spectrum of the guest material, the energy difference between the peak energy of the emission spectrum and the peak energy of the absorption band on the lowest energy side of the absorption spectrum is preferably within 0.3 eV. More preferably, it is within 0.2 eV, and most preferably, it is within 0.1 eV.

[0152] Furthermore, in one aspect of the invention, a singlet exciton of a first organic compound or a second organic compound is used to form an excitocomplex.

[0153] In one embodiment of the light-emitting element of the present invention, the basic process of forming an exciton complex involves the formation of a singlet exciton in one of the first and second organic compounds, followed by interaction with the other in the ground state. As described above, since the emission spectrum of the exciton complex largely overlaps with the absorption spectrum of the phosphorescent compound, the energy transfer efficiency can be improved. Therefore, a light-emitting element with high external quantum efficiency can be realized.

[0154] As mentioned above, the excitation lifetime of singlet excitons is short (τ is small), which leads to the following problem: before the excitation energy is transferred from the singlet exciton to the guest material, a portion of the excitation energy is deactivated (either by light emission or thermal deactivation) (as shown in formula (3)). (The tendency to decrease). However, in one aspect of the invention, since the singlet exciton rapidly forms an excitocomplex, the deactivation of this excitation energy can be suppressed. Moreover, it can be considered that the longer excitation lifetime of the excitocomplex is beneficial to energy transfer efficiency. Therefore, by applying one aspect of the present invention, the deactivation of the singlet excitation energy of the host material can be suppressed, which affects not only the efficiency of the element but also its lifetime, thereby enabling the realization of a long-life light-emitting element.

[0155] In one aspect of the invention, it is also preferable that the excitation energy of the excimer complex is sufficiently transferred to the phosphorescent compound, and that virtually no luminescence is observed from the excimer complex. Therefore, it is preferable to transfer energy to the phosphorescent compound via the excimer complex to cause the phosphorescent compound to emit phosphorescence.

[0156] As can be seen from the above concept of energy transfer, one aspect of the present invention is effective when at least one of the first organic compound and the second organic compound is a fluorescent compound (i.e., a compound that readily emits light from a singlet excited state or undergoes thermal deactivation). Therefore, it is preferable that at least one of the first organic compound and the second organic compound is a fluorescent compound.

[0157] Furthermore, when a phosphorescent compound is used as the host material, the organic compound itself readily emits light, but energy is not easily transferred to the guest material. In this case, it would be desirable for the organic compound to emit light efficiently, but due to the concentration quenching problem of the organic compound used as the host material, it is difficult to achieve high luminescence efficiency. Therefore, it is preferable that the organic compound is a fluorescent compound, and that it transfers energy through the structure described above.

[0158] Furthermore, in one aspect of the present invention, the phosphorescent compound is preferably an organometallic complex.

[0159] The following details the excitocomplex utilized in one aspect of the present invention.

[0160] <Exciton Complex>

[0161] Exciplexes are formed through interactions between dissimilar molecules in an excited state. It is generally known that exciplexes readily form between materials with relatively deep LUMO energy levels and materials with relatively shallow HOMO energy levels.

[0162] The emission wavelength depends on the energy difference between the HOMO and LUMO energy levels. When the energy difference is large, the emission wavelength is shorter, and when the energy difference is small, the emission wavelength is longer.

[0163] In this embodiment of the invention, the HOMO and LUMO energy levels of the first and second organic compounds are different. Specifically, the energy levels are arranged in the following order from low to high: HOMO energy level of the first organic compound < HOMO energy level of the second organic compound < LUMO energy level of the first organic compound < LUMO energy level of the second organic compound (refer to...) Figure 17 ).

[0164] When the above two organic compounds are used to form an excitocomplex, the LUMO level of the excitocomplex originates from the first organic compound, while the HOMO level originates from the second organic compound (see reference). Figure 17 Therefore, the energy difference of the exciton complex is smaller than that of the first organic compound and the second organic compound. In other words, the emission wavelength of the exciton complex is longer than that of the first and second organic compounds.

[0165] The formation process of the excitocomplex utilized in one aspect of the present invention can be broadly divided into two processes.

[0166] Electroplex

[0167] In this specification, the term "electroactive complex" refers to an excitocomplex formed directly using a first organic compound in its ground state and a second organic compound in its ground state.

[0168] As mentioned above, generally speaking, when electrons and holes recombine in the host material, the excitation energy is transferred from the excited state of the host material to the guest material, thereby causing the guest material to be in an excited state and emit light.

[0169] Here, before the excitation energy is transferred from the host material to the guest material, the host material itself emits light or the excitation energy is converted into thermal energy, causing partial deactivation of the excitation energy. In particular, when the host material is in a singlet excited state, the excitation lifetime is shorter compared to the case of a triplet excited state, making it prone to deactivation of the singlet excitation energy. The deactivation of the excitation energy is one of the reasons for the reduced lifetime of the light-emitting element.

[0170] However, in one aspect of the present invention, since a first organic compound having charge carriers (cations or anions) and a second organic compound are used to form an excitokinetic complex, the formation of singlet excitons with short excitation lifetimes can be suppressed. In other words, a process of directly forming the excitokinetic complex exists without the formation of singlet excitons. Therefore, the deactivation of the aforementioned singlet excitation energy can also be suppressed. Thus, a long-lifetime light-emitting element can be realized.

[0171] For example, when the first organic compound is an electron-trapping compound and the second organic compound is a hole-trapping compound, an electroexciton complex is directly formed using the anion of the first organic compound and the cation of the second organic compound. Previously, there was no concept of obtaining a high-efficiency light-emitting element by suppressing the occurrence of singlet excited states of the host material in the above manner and transferring energy from the electroexciton complex to the guest material. Furthermore, it can be considered that since the occurrence of triplet excited states of the host material is similarly suppressed, and an electroexciton complex is directly formed, energy is transferred from the electroexciton complex to the guest material. This mechanism is also previously unknown.

[0172] Furthermore, compared to the emission wavelengths of the first and second organic compounds, the emission spectrum of the formed electrostimulated complex is located on the longer wavelength side.

[0173] The overlap between the emission spectrum of the electroexcimer complex and the absorption spectrum of the phosphorescent compound is greater than the overlap between the emission spectrum of the first organic compound (or the second organic compound) and the absorption spectrum of the phosphorescent compound. One embodiment of the present invention provides a light-emitting element with high energy transfer efficiency because it utilizes the overlap between the emission spectrum of the electroexcimer complex and the absorption spectrum of the phosphorescent compound to transfer energy. Therefore, one embodiment of the present invention can realize a light-emitting element with high external quantum efficiency.

[0174] Formation of exciton complexes via excitons

[0175] As another process, a basic process can be considered whereby, after one of the first and second organic compounds forms a singlet exciton, it interacts with the ground state of the other to form an excitocomplex. Unlike electroexcitocomplexes, in this case, a singlet excited state of either the first or second organic compound is temporarily generated, but since this singlet excited state rapidly transforms into an excitocomplex, the deactivation of the singlet excitation energy can be suppressed. Thus, the deactivation of the excitation energy of either the first or second organic compound can be suppressed. Therefore, one aspect of the present invention can realize a long-lifetime light-emitting element. Furthermore, it can be considered that the triplet excited state of the host material also rapidly transforms into an excitocomplex, and energy is transferred from the excitocomplex to the guest material.

[0176] Compared to the emission wavelengths of the first and second organic compounds, the emission spectrum of the formed excitocomplex is located on the longer wavelength side.

[0177] The overlap between the emission spectrum of the excimer complex and the absorption spectrum of the phosphorescent compound is greater than the overlap between the emission spectrum of the first organic compound (or the second organic compound) and the absorption spectrum of the phosphorescent compound. One embodiment of the present invention provides a light-emitting element with high energy transfer efficiency because it utilizes the overlap between the emission spectrum of the excimer complex and the absorption spectrum of the phosphorescent compound to transfer energy. Therefore, one embodiment of the present invention can realize a light-emitting element with high external quantum efficiency.

[0178] For example, when the first organic compound is an electron-trapping compound and the second organic compound is a hole-trapping compound, and the difference between their HOMO and LUMO energy levels is large (specifically, greater than 0.3 eV), electrons are selectively injected into the first organic compound, and holes are selectively injected into the second organic compound. In this case, it can be considered that the formation of an electro-excitocomplex is preferentially carried out compared to the process of forming an excitocomplex via singlet excitons.

[0179] This implementation method can be appropriately combined with other implementation methods.

[0180] (Implementation Method 2)

[0181] In this embodiment, refer to Figures 16A to 16C This invention describes a light-emitting element according to one aspect of the present invention.

[0182] Figure 16A This is a diagram showing a light-emitting element having an EL layer 102 between the first electrode 103 and the second electrode 108. Figure 16A The light-emitting element includes a hole injection layer 701, a hole transport layer 702, a light-emitting layer 703, an electron transport layer 704, and an electron injection layer 705 stacked sequentially on a first electrode 103, and a second electrode 108 disposed thereon.

[0183] The first electrode 103 is preferably formed using any metal, alloy, conductive compound, or mixture thereof that has a high work function (specifically, 4.0 eV or higher). Specifically, examples include indium tin oxide (ITO), indium tin oxide containing silicon or silicon oxide, indium zinc oxide (IZO), and indium oxide containing tungsten oxide and zinc oxide (IWZO). These conductive metal oxide films are generally formed by sputtering, but can also be formed using sol-gel methods. For example, by sputtering, an indium oxide-zinc oxide film can be formed using a target containing 1 wt% to 20 wt% zinc oxide in indium oxide. Furthermore, by sputtering, an IWZO film can be formed using a target containing 0.5 wt% to 5 wt% tungsten oxide and 0.1 wt% to 1 wt% zinc oxide in indium oxide. In addition, examples include graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or nitrides of metallic materials (such as titanium nitride).

[0184] However, in the EL layer 102, when the layer formed in contact with the first electrode 103 is formed using a composite material consisting of a mixture of an organic compound and an electron acceptor (described later), any metal, alloy, conductive compound, or mixture thereof can be used as the material for the first electrode 103, regardless of the work function. For example, aluminum, silver, or aluminum-containing alloys (e.g., Al-Si) can also be used.

[0185] The first electrode 103 can be formed, for example, by sputtering or vapor deposition (including vacuum vapor deposition).

[0186] The second electrode 108 is preferably formed using any metal, alloy, conductive compound, or mixture thereof that has a low work function (preferably 3.8 eV or less). Specifically, materials that can be used include elements belonging to Group 1 or Group 2 of the periodic table, namely alkali metals such as lithium or cesium, alkaline earth metals such as calcium or strontium, magnesium, alloys containing the above metals (e.g., Mg-Ag, Al-Li), rare earth metals such as europium, ytterbium, alloys containing the above metals, aluminum, or silver.

[0187] However, when a composite material formed by mixing the organic compound and the electron donor described later is used in the layer formed in the EL layer 102 in contact with the second electrode 108, any of the various conductive materials can be used, such as Al, Ag, ITO, indium oxide-tin oxide containing silicon or silicon oxide, etc., without considering the magnitude of the work function.

[0188] Alternatively, vacuum evaporation or sputtering can be used to form the second electrode 108. Furthermore, when using silver paste, coating or inkjet printing methods can be employed.

[0189] The EL layer 102 has at least a light-emitting layer 703. A portion of the EL layer 102 can be made of known substances, and can be made of either low-molecular-weight compounds or high-molecular-weight compounds. In addition, the substances forming the EL layer 102 include not only substances composed solely of organic compounds, but also substances in which a portion of the substance comprises inorganic compounds.

[0190] In addition to the light-emitting layer 703, EL layer 102 also includes other components such as EL layer 102. Figure 16A As shown, it also includes appropriate combinations of the following layers: a hole injection layer 701 with a substance having high hole injection capacity, a hole transport layer 702 with a substance having high hole transport capacity, an electron transport layer 704 with a substance having high electron transport capacity, and an electron injection layer 705 with a substance having high electron injection capacity, etc.

[0191] Hole injection layer 701 is a layer containing a material with high hole injection properties. As a material with high hole injection properties, metal oxides can be used, such as molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungsten oxide, or manganese oxide. Alternatively, phthalocyanine compounds, such as phthalocyanine (abbreviation: H2Pc) or copper phthalocyanine(II) (abbreviation: CuPc), can also be used.

[0192] Alternatively, aromatic amine compounds of low molecular weight organic compounds such as 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 (abbreviation: DPAB), and 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DPAB) Abbreviations: DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B), 3-[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), etc.

[0193] Alternatively, polymers (e.g., oligomers, dendrimers, or polymers) can be used, such as poly(N-vinylcarbazole) (PVK), poly(4-vinyltriphenylamine) (PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide] (PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (Poly-TPD), as well as polymers with added acids, such as poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS) or polyaniline / poly(styrenesulfonic acid) (PAni / PSS), etc.

[0194] A composite material formed by mixing an organic compound with an electron acceptor can be used in the hole injection layer 701. This composite material exhibits excellent hole injection and hole transport properties because it generates holes in the organic compound through the electron acceptor. In this case, the organic compound is preferably a material with excellent performance in transporting generated holes (a substance with high hole transport properties).

[0195] Various compounds, such as aromatic amine compounds, carbazole derivatives, aromatic hydrocarbons, and polymers (e.g., oligomers, dendritic polymers, or polymers), can be used as organic compounds for the composite material. Organic compounds with high hole transport properties are preferred as the organic compound for this composite material. Specifically, organic compounds with a hole mobility of 10 are preferred. -6 cm 2 Substances with a density of / Vs or higher. Note that, in addition to the substances mentioned above, any substance with hole transport properties higher than electron transport properties can also be used. Below are specific examples of organic compounds that can be used in composite materials.

[0196] Organic compounds that can be used in this composite material can be, for example, aromatic amine compounds, such as TDATA, MTDATA, DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4-phenyl-4'-(9-phenylfluorene) -9-yl)triphenylamine (abbreviation: BPAFLP); and carbazole derivatives, such as 4,4'-bis(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-anthrayl)phenyl]-9H-carbazole (abbreviation: PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

[0197] Other examples of organic compounds that can be used are aromatic hydrocarbons, such as 2-tert-butyl-9,10-bis(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10-bis(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), and 9,10-bis(2-naphthyl)anthracene. 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-bis(1-naphthyl)anthracene.

[0198] Other examples of organic compounds that can be used are aromatic hydrocarbons, such as 2,3,6,7-tetramethyl-9,10-bis(2-naphthyl)anthracene, 9,9'-bianthracene, 10,10'-diphenyl-9,9'-bianthracene, 10,10'-bis(2-phenylphenyl)-9,9'-bianthracene, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthracene, anthracene, tetraphenylene, rubrogene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, pentaphenylene, benzobenzene, 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVPA), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), etc.

[0199] In addition, examples of electron acceptors include organic compounds such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinone dimethane (abbreviation: F4-TCNQ) and chloroquinone, as well as transition metal oxides and oxides of metals belonging to Groups 4 to 8 of the periodic table. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferred because these metal oxides have high electron acceptability. Among them, molybdenum oxide is particularly preferred because it is stable in the atmosphere, has low hygroscopicity, and is easy to handle.

[0200] The aforementioned polymeric compounds, such as PVK, PVTPA, PTPDMA, or Poly-TPD, and the aforementioned electron acceptors can be used to form a composite material, which is then used in the hole injection layer 701.

[0201] Hole transport layer 702 is a layer containing a substance with high hole transport capacity. As a substance with high hole transport capacity, aromatic amine compounds can be used, such as NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluorene-2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi) or 4,4'-bis[N-(spirocyclic-9,9'-difluorene-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), etc. The substance described herein is primarily characterized by a hole mobility of 10. -6 cm 2 Substances with a hole transport capacity of / Vs or higher. Note that, in addition to the substances mentioned above, any substance with a hole transport capacity higher than that with an electron transport capacity can be used. Furthermore, the layer containing a substance with high hole transport capacity is not limited to a single layer; two or more layers containing any of the aforementioned substances can also be stacked.

[0202] As the hole transport layer 702, carbazole derivatives such as CBP, CzPA, and PCzPA, or anthracene derivatives such as t-BuDNA, DNA, and DPANth can also be used.

[0203] As the hole transport layer 702, polymeric compounds such as PVK, PVTPA, PTPDMA, or Poly-TPD can also be used.

[0204] The light-emitting layer 703 is a layer containing a luminescent substance. In this embodiment, the light-emitting layer 703 comprises a phosphorescent compound, a first organic compound, and a second organic compound. The phosphorescent compound is the luminescent substance (guest material). In the light-emitting layer 703, the compound with a higher content than the first organic compound and the second organic compound is the host material. Specifically, please refer to Embodiment 1.

[0205] Organometallic complexes are preferred as phosphorescent compounds, and iridium complexes are particularly preferred. Furthermore, considering the energy transfer via the Foster mechanism described above, the molar absorptivity of the absorption band located on the longest wavelength side of the phosphorescent compound is preferably... The above, especially preferred above. Examples of compounds with such large molar absorptivity include, for instance, bis(3,5-dimethyl-2-phenylpyrazine) (di-neopentylmethane)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]), (acetylacetonate) bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), bis(2,3,5-triphenylpyrazine) (di-neopentylmethane)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), (acetylacetonate) bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), (acetylacetonate) bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), etc. Especially when using molar absorptivity to achieve When using materials such as [Ir(dppm)2(acac)], light-emitting elements with an external quantum efficiency of around 30% can be obtained.

[0206] As the first and second organic compounds, it is preferable to use a combination of any one of electron-accepting compounds (typically heteroaromatic compounds) and any one of hole-accepting compounds (typically aromatic amine compounds and carbazole compounds). Examples of electron-accepting compounds include 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[4-(3,6-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), and 2-[4-(3,6-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II). [-Diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II), 2-[4-(dibenzothiophen-4-yl)phenyl]-1-phenyl 1H-benzimidazole (abbreviation: DBTBIm-II), and examples of hole-accepting compounds include 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP), and 4,4'-bis(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBN). Examples of compounds used in luminescence include αNBA1BP (4-(1-naphthyl)-4'-phenyltriphenylamine), 2,7-bis[N-(diphenylaminophenyl)-N-phenylamino]-spirocyclic-9,9'-bifluorene (DPA2SF), 4,4',4''-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (1'-TNATA), and 9-phenyl-9H-3-(9-phenyl-9H-carbazole-3-yl)carbazole (PCCP). By employing these structures, not only can the effect of improving luminescence efficiency and lifetime be achieved through energy transfer from the exciton complex, but also by improving luminescence efficiency and lifetime through adjusting the carrier balance of hole and electron transport within the luminescent layer. However, this invention is not limited to these compounds; any combination capable of forming an exciton complex is acceptable.

[0207] Furthermore, excitocomplexes can also be formed at the interface between two layers. For example, when a layer containing a second organic compound and a layer containing a first organic compound are stacked, an excitocomplex is formed near their interface. These two layers can be used as the luminescent layer in one embodiment of the present invention. In this case, a phosphorescent compound can be added near the interface. Alternatively, a phosphorescent compound can be added to one or both of the two layers.

[0208] Electron transport layer 704 is a layer containing a substance with high electron transport properties. Examples of substances with high electron transport properties include metal complexes such as Alq3, tris(4-methyl-8-hydroxyquinoline) aluminum (abbreviation: Almq3), bis(10-hydroxybenzo[h]hydroxyquinoline) beryllium (abbreviation: BeBq2), BAlq, Zn(BOX)2, and bis[2-(2-hydroxyphenyl)benzothiazole]zinc (abbreviation: Zn(BTZ)2), etc. In addition, heteroaromatic compounds such as 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (abbreviation: OXD-7), 3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenyl)-1,2,4-triazole (abbreviation: p-EtTAZ), phenanthrene-2-ylene (abbreviation: BPhen), copper hydroxide (abbreviation: BCP), and 4,4'-bis(5-methylbenzoxazole-2-yl)stilbene (abbreviation: BzOs) can also be used. In addition, polymeric compounds such as poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-copolymer-(pyridine-3,5-diyl)] (abbreviation: PF-Py), and poly[(9,9-dioctylfluorene-2,7-diyl)-copolymer-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy) can also be used. The substances described herein primarily possess 10 - 6 cm 2 Materials with an electron mobility of / Vs or higher. Note that any material other than those mentioned above can be used as an electron transport layer, provided that its hole transport capability is higher than its electron transport capability.

[0209] In addition, the electron transport layer is not limited to a single layer, but can also be a stack of two or more layers containing any of the above-mentioned substances.

[0210] Electron injection layer 705 is a layer containing a material with high electron injection capability. Electron injection layer 705 may use alkali metals, alkaline earth metals and their compounds, such as lithium, cesium, calcium, lithium fluoride, cesium fluoride, calcium fluoride and lithium oxide; rare earth metal compounds such as erbium fluoride and the aforementioned materials used for electron transport layer 704.

[0211] Alternatively, a composite material formed by mixing an organic compound with an electron donor can be used for the electron injection layer 705. This composite material exhibits excellent electron injection and electron transport properties because it generates electrons in the organic compound through the electron donor. In this case, the organic compound is preferably a material with excellent performance in transporting the generated electrons. Specifically, for example, any of the substances constituting the electron transport layer 704 described above (e.g., metal complexes or heteroaromatic compounds) can be used. A substance exhibiting electron-donating properties to the organic compound can be used as the electron donor. Specifically, alkali metals, alkaline earth metals, and rare earth metals, such as lithium, cesium, magnesium, calcium, erbium, and ytterbium, are preferred. Furthermore, any alkali metal oxide or alkaline earth metal oxide, such as lithium oxide, calcium oxide, and barium oxide, as well as Lewis bases such as magnesium oxide or organic compounds such as tetrathiofulvalene (TTF), are preferred.

[0212] Note that the hole injection layer 701, hole transport layer 702, light-emitting layer 703, electron transport layer 704 and electron injection layer 705 can be formed by vapor deposition (including vacuum vapor deposition), inkjet printing or coating, etc.

[0213] like Figure 16B As shown, multiple EL layers can also be stacked between the first electrode 103 and the second electrode 108. In this case, it is preferable to provide a charge generating layer 803 between the stacked first EL layer 800 and the second EL layer 801. The charge generating layer 803 can be formed using the aforementioned composite material. Alternatively, the charge generating layer 803 can also be a stacked structure comprising layers containing composite materials and layers containing other materials. In this case, layers containing electron-donating substances and substances with high electron transport properties, or layers composed of transparent conductive films, can be used as layers containing other materials. Light-emitting elements with this structure are less prone to problems such as energy transfer or quenching, and because the range of materials that can be selected can be expanded, light-emitting elements with both high luminous efficiency and long lifetime can be easily obtained. In addition, light-emitting elements that emit phosphorescence from one EL layer and fluorescence from another EL layer can be easily obtained. This structure can be used in combination with the aforementioned EL layer structure.

[0214] Furthermore, by making the emitted colors of each EL layer different, the light-emitting element as a whole can emit light of the desired color. For example, in a light-emitting element with two EL layers, the light emitted by the first and second EL layers can be made complementary, thus resulting in a light-emitting element that emits white light as a whole. This can be applied to light-emitting elements with three or more EL layers.

[0215] like Figure 16CAs shown, the EL layer 102 may also have a hole injection layer 701, a hole transport layer 702, a light-emitting layer 703, an electron transport layer 704, an electron injection buffer layer 706, an electron relay layer 707, and a composite material layer 708 in contact with the second electrode 108 between the first electrode 103 and the second electrode 108.

[0216] By providing a composite material layer 708 in contact with the second electrode 108, especially when the second electrode 108 is formed using a sputtering method, damage to the EL layer 102 can be reduced, which is therefore preferred. The composite material layer 708 can be formed using the aforementioned composite material, wherein the organic compound having high hole transport capacity contains an acceptor substance.

[0217] Furthermore, by providing an electron injection buffer layer 706, the injection barrier between the composite material layer 708 and the electron transport layer 704 can be weakened, thereby making it easier to inject electrons generated in the composite material layer 708 into the electron transport layer 704.

[0218] As the electron injection buffer layer 706, the following materials with high electron injection capability can be used: alkali metals; alkaline earth metals; rare earth metals and their compounds (e.g., alkali metal compounds (including oxides such as lithium oxide, halides, carbonates such as lithium carbonate or cesium carbonate), alkaline earth metal compounds (including oxides, halides, carbonates), or rare earth metal compounds (including oxides, halides, carbonates)).

[0219] When the electron injection buffer layer 706 comprises a substance with high electron transport capacity and a donor substance, it is preferable to add the donor substance such that the mass ratio of the donor substance to the substance with high electron transport capacity is 0.001:1 to 0.1:1. Alternatively, the donor substance can be organic compounds such as tetrathianaphthacene (TTN), nickel dicerocene or decamethylnickel dicerocene, and alkali metals, alkaline earth metals, rare earth metals and their compounds (e.g., alkali metal compounds (including oxides such as lithium oxide, halides, carbonates such as lithium carbonate or cesium carbonate), alkaline earth metal compounds (including oxides, halides and carbonates), rare earth metal compounds (including oxides, halides and carbonates)). Furthermore, the substance with high electron transport capacity can be formed using the same material as the electron transport layer 704 described above.

[0220] Furthermore, it is preferable to form an electron relay layer 707 between the electron injection buffer layer 706 and the composite material layer 708. The electron relay layer 707 is not strictly necessary, but by providing an electron relay layer 707 with high electron transport capacity, electrons can be rapidly transported to the electron injection buffer layer 706.

[0221] The structure in which the electron relay layer 707 is sandwiched between the composite material layer 708 and the electron injection buffer layer 706 ensures that the acceptor material contained in the composite material layer 708 and the donor material contained in the electron injection buffer layer 706 do not easily interact with each other and do not easily affect their respective functions. Therefore, it can prevent the driving voltage from increasing.

[0222] The electron relay layer 707 contains a material with high electron transport capability, and the LUMO energy level of this material is set between the LUMO energy level of the acceptor material contained in the composite material layer 708 and the LUMO energy level of the material with high electron transport capability contained in the electron transport layer 704. Furthermore, when the electron relay layer 707 contains a donor material, the donor energy level of this donor material is also set between the LUMO energy level of the acceptor material contained in the composite material layer 708 and the LUMO energy level of the material with high electron transport capability contained in the electron transport layer 704. Regarding the specific values ​​of the energy levels, it is preferable that the LUMO energy level of the material with high electron transport capability contained in the electron relay layer 707 is greater than or equal to -5.0 eV, more preferably greater than or equal to -5.0 eV and less than or equal to -3.0 eV.

[0223] The material containing the electronic relay layer 707 with high electron transport properties is preferably a phthalocyanine material or a metal complex having metal-oxygen bonds and aromatic ligands.

[0224] As the phthalocyanine material included in the electronic relay layer 707, specifically, any one of the following substances is preferred: CuPc; SnPc (Phthalocyanine tin(II) complex); ZnPc (Phthalocyanine zinc complex); CoPc (Cobalt(II) phthalocyanine, β-form). Type); FePc (Phthalocyanine Iron) and PhO-VOPc (Vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine).

[0225] As the metal complex containing a metal-oxygen bond and aromatic ligands included in the electronic relay layer 707, a metal complex having a metal-oxygen double bond is preferred. Since the metal-oxygen double bond has acceptor properties (the property of readily accepting electrons), electron movement (donation and acceptance) becomes easier. Furthermore, metal complexes having metal-oxygen double bonds are considered stable. Therefore, by using a metal complex having a metal-oxygen double bond, the light-emitting element can be driven more stably at lower voltages.

[0226] Phthalocyanine materials are preferred as metal complexes containing metal-oxygen bonds and aromatic ligands. Specifically, any one of VOPc (Vanadyl phthalocyanine), SnOPc (Phthalocyanine tin(IV)oxide complex), and TiOPc (Phthalocyanine titanium oxide complex) is preferred because the metal-oxygen double bond in the molecular structure readily interacts with other molecules and has high acceptor activity.

[0227] Furthermore, as the aforementioned phthalocyanine materials, phthalocyanine materials having a phenoxy group are preferred. Specifically, phthalocyanine derivatives having a phenoxy group, such as PhO-VOPc, are preferred. Phthalocyanine derivatives having a phenoxy group are soluble in solvents. Therefore, they have the advantages of being easy to handle when forming light-emitting elements and easy to maintain the device used for film formation.

[0228] The electronic relay layer 707 may also contain donor materials. As donor materials, the following substances may be used: organic compounds such as tetrathianaphthacene (TTN), nickel dicerocene or decamethylnickel dicerocene, and alkali metals, alkaline earth metals, rare earth metals and their compounds (e.g., alkali metal compounds (including oxides such as lithium oxide, halides, carbonates such as lithium carbonate or cesium carbonate), alkaline earth metal compounds (including oxides, halides, carbonates), and rare earth metal compounds (including oxides, halides, carbonates)). When these donor materials are included in the electronic relay layer 707, electrons are readily mobile, enabling the light-emitting element to be driven at a lower voltage.

[0229] When the donor material is included in the electron relay layer 707, materials with high electron transport properties, in addition to those mentioned above, can also be used that have a LUMO energy level higher than the acceptor energy level of the acceptor material included in the composite material layer 708. Specifically, materials with a LUMO energy level of -5.0 eV or higher are preferred, and materials with a LUMO energy level of -5.0 eV or higher and -3.0 eV or lower are more preferred. Examples of such materials include perylene derivatives and nitrogen-containing fused-ring aromatic compounds. Furthermore, nitrogen-containing fused-ring aromatic compounds are preferred for use in the electron relay layer 707 because they have high stability.

[0230] Specific examples of perylene derivatives include: 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA); 3,4,9,10-perylenetetracarboxylic acid bisbenzimidazole (PTCBI); N,N'-dioctyl-3,4,9,10-perylenetetracarboxylic acid diimide (PTCDI-C8H); N,N'-dihexyl-3,4,9,10-perylenetetracarboxylic acid diimide (Hex PTC), etc.

[0231] Specific examples of nitrogen-containing fused-ring aromatic compounds include: pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarboxynitrile (abbreviation: PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazabenzophenanthrene (abbreviation: HAT(CN)6); 2,3-diphenylpyridino[2,3-b]pyrazine (abbreviation: 2PYPR); 2,3-bis(4-fluorophenyl)pyridino[2,3-b]pyrazine (abbreviation: F2PYPR), etc.

[0232] In addition to the substances mentioned above, the following substances may also be used: 7,7,8,8-tetracyano-p-quinone dimethyl ether (abbreviation: TCNQ); 1,4,5,8-naphthalenetetracarboxylic acid dianhydride (abbreviation: NTCDA); perfluoropentacene; hexadecylfluorocopper phthalocyanine (abbreviation: F... 16 CuPc); N,N'-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (abbreviation: NTCDI-C8F), 3',4'-dibutyl-5,5''-bis(dicyanomethylene)-5,5''-dihydro-2,2':5',2''-trithiophene (abbreviation: DCMT), methylene fullerene (e.g., [6,6]-phenylC 61 Methyl butyrate, etc.

[0233] In addition, when the electron relay layer 707 contains a donor material, the electron relay layer 707 can be formed by, for example, co-evaporating a material with high electron transport properties and a donor material.

[0234] The hole injection layer 701, hole transport layer 702, light emission layer 703, and electron transport layer 704 can be formed using the materials described above.

[0235] The EL layer 102 of this embodiment can be manufactured through the above steps.

[0236] In the aforementioned light-emitting element, current flows due to the potential difference generated between the first electrode 103 and the second electrode 108, and light is emitted due to the recombination of holes and electrons in the EL layer 102. Furthermore, this light emission is extracted to the outside through either or both of the first electrode 103 and the second electrode 108. Therefore, either or both of the first electrode 103 and the second electrode 108 become electrodes that are transparent to visible light.

[0237] Furthermore, the structure of the layer disposed between the first electrode 103 and the second electrode 108 is not limited to the structure described above. A structure different from the one described above can also be used, as long as the portion away from the first electrode 103 and the second electrode 108 has a light-emitting region for hole-electron recombination to prevent quenching caused by the light-emitting region approaching the metal.

[0238] In other words, there are no particular restrictions on the stacked structure of the layers. Layers containing substances with high electron transport, high hole transport, high electron injection, high hole injection, bipolar substances (substances with both high electron and high hole transport) or hole blocking materials can be freely combined with light-emitting layers.

[0239] By using the light-emitting element shown in this embodiment, a passive matrix light-emitting device or an active matrix light-emitting device driven by a transistor-controlled light-emitting element can be manufactured. Furthermore, this light-emitting device can be applied to electronic devices or lighting devices, etc.

[0240] As described above, a light-emitting element according to one aspect of the present invention can be manufactured.

[0241] This implementation method can be appropriately combined with any other implementation method.

[0242] [Example 1]

[0243] In this embodiment, refer to Figure 1A and Figure 1B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0244] The phosphorescent compound used in this embodiment is bis(3,5-dimethyl-2-phenylpyrazine)(dineopentaylmethane)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)]). The first organic compound used in this embodiment is 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II). The second organic compound used in this embodiment is 4,4'-bis(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCCNBB). The chemical formulas of the materials used in this embodiment are shown below.

[0245]

[0246] <Absorption Spectroscopy>

[0247] Figure 1A and Figure 1B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(mppr-Me)2(dpm)] as a phosphorescent compound is shown. In the absorption spectrum measurement, a UV-Vis spectrophotometer (JASCO Corporation V550 model) was used. The dichloromethane solution (0.093 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0248] <Emission Spectrum>

[0249] Figure 1A and Figure 1B The emission spectra of a thin film of 2mDBTPDBq-II as the first organic compound (emission spectrum 1), the emission spectrum of a thin film of PCCNBB as the second organic compound (emission spectrum 2), and the emission spectrum of a thin film of a mixture of 2mDBTPDBq-II and PCCNBB are also shown (emission spectrum 3). Figure 1A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 1B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0250] from Figure 1A The absorption spectrum shows that [Ir(mppr-Me)2(dpm)] has a broad absorption band around 520 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0251] Compared to emission spectra 1 and 2, the peak of emission spectrum 3 is located on the longer wavelength (lower energy) side. Furthermore, the peak of emission spectrum 3 is located closer to the absorption band compared to the peaks of emission spectra 1 and 2. Figure 1A and Figure 1B It can be seen that the emission spectrum with the greatest overlap with the absorption band that contributes significantly to luminescence in the absorption spectrum is emission spectrum 3. Specifically, the difference between the peak value of this absorption band in the absorption spectrum (the shoulder peak near 520 nm) and the peak value of emission spectrum 3 is 0.04 eV.

[0252] Compared to the emission spectrum of the monomer, the emission spectrum of the mixture of 2mDBTPDBq-II and PCNBB shows a peak at longer wavelengths (lower energy). This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and PCNBB.

[0253] It was found that the emission spectrum of this hybrid material largely overlaps with the absorption spectrum of [Ir(mppr-Me)2(dpm)], where the absorption bands that can be considered to contribute significantly to luminescence are located. Therefore, since the light-emitting element using the hybrid material of 2mDBTPDBq-II and PCNBB and [Ir(mppr-Me)2(dpm)] utilizes the overlap between the emission spectrum of this hybrid material and the absorption spectrum of the phosphorescent compound to transfer energy, the energy transfer efficiency is high. Thus, a light-emitting element with high external quantum efficiency can be obtained.

[0254] [Example 2]

[0255] In this embodiment, refer to Figure 2A and Figure 2B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0256] The phosphorescent compound used in this embodiment is (acetylacetonate)bis(4,6-diphenylpyrimidine)iridium(III) (abbreviated: [Ir(dppm)2(acac)]). The first organic compound used in this embodiment is 2mDBTPDBq-II. The second organic compound used in this embodiment is PCCNBB. The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in Example 1 are omitted.

[0257]

[0258] <Absorption Spectroscopy>

[0259] Figure 2A and Figure 2BThe UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(dppm)2(acac)] as a phosphorescent compound is shown. In the absorption spectrum measurement, a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.) was used. The dichloromethane solution (0.093 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0260] <Emission Spectrum>

[0261] also, Figure 2A and Figure 2B The emission spectra of the thin film of 2mDBTPDBq-II as the first organic compound are shown (emission spectrum 4), the emission spectrum of the thin film of PCCNBB as the second organic compound is shown (emission spectrum 5), and the emission spectrum of the thin film of a mixture of 2mDBTPDBq-II and PCCNBB is shown (emission spectrum 6). Figure 2A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 2B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0262] from Figure 2A The absorption spectrum shows that [Ir(dppm)2(acac)] has a broad absorption band around 520 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0263] Compared to emission spectra 4 and 5, the peak of emission spectrum 6 is located on the longer wavelength (lower energy) side. Furthermore, the peak of emission spectrum 6 is located closer to the absorption band compared to the peaks of emission spectra 4 and 5. Figure 2A and Figure 2B It can be seen that the emission spectrum with the greatest overlap with the absorption band that contributes significantly to luminescence in the absorption spectrum is emission spectrum 6. Specifically, the difference between the peak value (515 nm) of this absorption band in the absorption spectrum and the peak value of emission spectrum 6 is 0.02 eV.

[0264] Compared to the emission spectrum of the monomer, the emission spectrum of the mixture of 2mDBTPDBq-II and PCNBB shows a peak at longer wavelengths (lower energy). This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and PCNBB.

[0265] It was found that the peak of the emission spectrum of this hybrid material largely overlaps with the absorption band in the absorption spectrum of [Ir(dppm)2(acac)], which is considered to contribute significantly to luminescence. Therefore, since the light-emitting element containing the hybrid material of 2mDBTPDBq-II and PCNBB and [Ir(dppm)2(acac)] transfers energy by utilizing the overlap between the emission spectrum of this hybrid material and the absorption spectrum of the phosphorescent compound, the energy transfer efficiency is high. Thus, a light-emitting element with high external quantum efficiency can be obtained.

[0266] [Example 3]

[0267] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. The chemical formulas of the materials used in this embodiment are shown below. Additionally, the chemical formulas of the materials used in the above embodiments are omitted.

[0268]

[0269] The following shows the manufacturing methods of the light-emitting element 1 and the comparative light-emitting element 2 in this embodiment.

[0270] (Light-emitting element 1)

[0271] First, an indium tin oxide (ITSO) film containing silicon oxide is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0272] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0273] Then, the substrate is placed inside and depressurized to 10. -4 In a vacuum evaporation apparatus at approximately Pa, the substrate 1100 is vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, and then cooled for approximately 30 minutes.

[0274] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4At approximately Pa, 4-phenyl-4'-(9-phenylfluorene-9-yl)triphenylamine (abbreviation: BPAFLP) and molybdenum oxide (VI) are co-deposited on the first electrode 1101 to form a hole injection layer 1111. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of BPAFLP to molybdenum oxide is adjusted to 4:2 (=BPAFLP:molybdenum oxide).

[0275] Next, a BPAFLP with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0276] Furthermore, 2mDBTPDBq-II, PCNBB, and [Ir(mppr-Me)2(dpm)] are co-deposited to form an emissive layer 1113 on the hole transport layer 1112. Here, the weight ratio of 2mDBTPDBq-II, PCNBB, and [Ir(mppr-Me)2(dpm)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II:PCNBB:[Ir(mppr-Me)2(dpm)]). The thickness of the emissive layer 1113 is set to 40nm.

[0277] Next, a 2mDBTPDBq-II film with a thickness of 10nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0278] Next, a red phenanthrene (BPhen) film with a thickness of 20 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0279] Then, a lithium fluoride (LiF) film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0280] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition to serve as the second electrode 1103 for use as the cathode, thereby manufacturing the light-emitting element 1 of this embodiment.

[0281] (Compare with light-emitting element 2)

[0282] The light-emitting layer 1113 of the contrast light-emitting element 2 is formed by co-depositing 2mDBTPDBq-II and [Ir(mppr-Me)2(dpm)]. Here, the weight ratio of 2mDBTPDBq-II and [Ir(mppr-Me)2(dpm)] is adjusted to 1:0.05 (=2mDBTPDBq-II:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 40nm. Except for the light-emitting layer 1113, it is manufactured in the same manner as the light-emitting element 1.

[0283] Note that resistance heating was used for evaporation in all of the above processes.

[0284] Table 1 shows the element structures of light-emitting element 1 and comparative light-emitting element 2 obtained through the above steps.

[0285] [Table 1]

[0286]

[0287] In a glove box under a nitrogen atmosphere, light-emitting element 1 and control light-emitting element 2 were sealed in a manner that prevented them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Note that the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0288] Figure 3 The current density-luminance characteristics of light-emitting element 1 and contrasting light-emitting element 2 are shown. Figure 3 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ).in addition, Figure 4 The voltage-brightness characteristics are shown. Figure 4 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 5 The brightness-current efficiency characteristics are shown. Figure 5 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 6 The brightness-external quantum efficiency characteristics are shown. Figure 6 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0289] Furthermore, Table 2 shows the brightness of light-emitting element 1 and contrasting light-emitting element 2 at approximately 1000 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0290] [Table 2]

[0291]

[0292] Figure 7 The emission spectra are shown when a current of 0.1 mA flows through light-emitting element 1 and contrast light-emitting element 2. Figure 7In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 2, 1200 cd / m 2 The CIE color coordinates of the light-emitting element 1 at the specified brightness are (x, y) = (0.56, 0.44), 960 cd / m². 2 The CIE color coordinates of the contrasting light-emitting element 2 at the given brightness are (x, y) = (0.55, 0.44). From the above results, it can be seen that light-emitting element 1 and contrasting light-emitting element 2 display orange light originating from [Ir(mppr-Me)2(dpm)].

[0293] From Table 2 and Figures 3 to 6 It can be seen that the current efficiency, power efficiency and external quantum efficiency of the light-emitting element 1 are higher than those of the light-emitting element 2.

[0294] In the light-emitting element 1 of this embodiment, 2mDBTPDBq-II, PCCNBB, and [Ir(mppr-Me)2(dpm)] shown in Example 1 are used as the light-emitting layer. As can be seen from Example 1, compared with the emission spectrum of the 2mDBTPDBq-II or PCCNBB monomer, the emission spectrum of the mixed material of 2mDBTPDBq-II and PCCNBB (emission spectrum of the excitocomplex) overlaps significantly with the absorption spectrum of [Ir(mppr-Me)2(dpm)]. Since the light-emitting element 1 of this embodiment utilizes this overlap for energy transfer, it can be considered to have high energy transfer efficiency, and therefore has higher external quantum efficiency compared with the comparative light-emitting element 2.

[0295] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0296] Next, reliability tests were conducted on light-emitting element 1 and comparison light-emitting element 2. Figure 8 The results of the reliability test are shown. Figure 8 In the diagram, the vertical axis represents the normalized brightness (%) with the initial brightness set to 100%, while the horizontal axis represents the driving time (h) of the element.

[0297] In reliability testing, the initial brightness was set to 5000 cd / m². 2 And under the condition of constant current density, it drives the light-emitting element 1 and the contrast light-emitting element 2.

[0298] After 120 hours, the brightness of light-emitting element 2 was 58% of its initial brightness. After 630 hours, the brightness of light-emitting element 1 was 65% of its initial brightness. These results indicate that the lifespan of light-emitting element 1 is longer than that of light-emitting element 2.

[0299] As can be seen from the above results, a highly reliable component can be achieved by applying one aspect of the present invention.

[0300] [Example 4]

[0301] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0302] The following describes a method for manufacturing the light-emitting element 3 in this embodiment.

[0303] (Light-emitting element 3)

[0304] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0305] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0306] Then, the substrate is placed inside and the pressure is reduced to 10. -4 In a vacuum evaporation apparatus at approximately Pa, the substrate 1100 is vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, and then cooled for approximately 30 minutes.

[0307] Next, the substrate 1100 with the first electrode 1101 formed thereon is fixed on the substrate support inside the vacuum evaporation apparatus with the surface where the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4 The hole injection layer 1111 is formed by co-depositing BPAFLP and molybdenum oxide (VI) on the first electrode 1101 at a thickness of approximately 40 nm. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of BPAFLP to molybdenum oxide is adjusted to 4:2 (=BPAFLP:molybdenum oxide).

[0308] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0309] Furthermore, 2mDBTPDBq-II, PCNBB, and [Ir(dppm)2(acac)] are co-deposited on the hole transport layer 1112 to form a light-emitting layer 1113. Here, the weight ratio of 2mDBTPDBq-II, PCNBB, and [Ir(dppm)2(acac)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II:PCNBB:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40nm.

[0310] Next, a 2mDBTPDBq-II film with a thickness of 10nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0311] Next, a BPhen film with a thickness of 20 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0312] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0313] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 3 of this embodiment.

[0314] Note that resistance heating was used for evaporation in all of the above processes.

[0315] Table 3 shows the element structure of the light-emitting element 3 obtained through the above steps.

[0316] [Table 3]

[0317]

[0318] The light-emitting element 3 was sealed in a glove box under a nitrogen atmosphere to prevent it from being exposed to the atmosphere, and then the operating characteristics of the light-emitting element were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0319] Figure 9 The current density-luminance characteristics of the light-emitting element 3 are shown. Figure 9 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 10 The voltage-brightness characteristics are shown. Figure 10 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 11 The brightness-current efficiency characteristics are shown. Figure 11 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 12 The brightness-external quantum efficiency characteristics are shown. Figure 12 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0320] Furthermore, Table 4 shows the light-emitting element 3 at a brightness of 1100 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0321] [Table 4]

[0322]

[0323] Figure 13 The emission spectrum is shown when a current of 0.1 mA is applied to the light-emitting element 3. Figure 13 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 4, 1100 cd / m 2 The CIE color coordinates of the light-emitting element 3 at the specified brightness are (x, y) = (0.54, 0.46). From the above results, it can be seen that the light-emitting element 3 displays orange light originating from [Ir(dppm)2(acac)].

[0324] From Table 4 and Figures 9 to 12 It can be seen that the light-emitting element 3 has relatively high current efficiency, power efficiency, and external quantum efficiency. In particular, it has an efficiency of 1100 cd / m². 2 At the desired brightness, the external quantum efficiency of the light-emitting element 3 is extremely high, at 28%. As mentioned above, the upper limit of the external quantum efficiency is considered to be around 25%. However, this result exceeds that limit.

[0325] In the light-emitting element of this embodiment, 2mDBTPDBq-II, PCNBB, and [Ir(dppm)2(acac)] shown in Example 2 are used as the light-emitting layer. As can be seen from Example 2, compared to the emission spectra of the individual 2mDBTPDBq-II or PCNBB monomers, the emission spectrum of the mixed material of 2mDBTPDBq-II and PCNBB (the emission spectrum of the excitocomplex) overlaps significantly with the absorption spectrum of [Ir(dppm)2(acac)]. Since the light-emitting element of this embodiment utilizes this overlap for energy transfer, it can be considered to have high energy transfer efficiency, achieving a previously unrealized high external quantum efficiency.

[0326] The results of Example 2 show that the peak value of the absorption band on the longest wavelength side of the absorption spectrum of the guest material used for the light-emitting element 3 is close to the peak value of the emission spectrum, and the molar absorptivity of this peak value is relatively large (>). The results above show that the light-emitting element 3 has extremely high energy transfer efficiency, and therefore has a high external quantum efficiency that has never been achieved before.

[0327] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0328] Next, a reliability test was conducted on the light-emitting element 3. Figure 14 The results of the reliability test are shown. Figure 14 In the diagram, the vertical axis represents the normalized brightness (%) with the initial brightness set to 100%, while the horizontal axis represents the driving time (h) of the element.

[0329] In reliability testing, the initial brightness was set to 5000 cd / m². 2 And it drives the light-emitting element 3 under the condition of constant current density.

[0330] The light-emitting element 3 retains 92% of its initial brightness after being driven for 320 hours.

[0331] As can be seen from the above results, a highly reliable component can be achieved by applying one aspect of the present invention.

[0332] [Example 5]

[0333] In this embodiment, refer to Figure 18A and Figure 18B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0334] The phosphorescent compound used in this embodiment is [Ir(dppm)2(acac)]. The first organic compound used in this embodiment is 2mDBTPDBq-II. The second organic compound used in this embodiment is 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP). The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in the above embodiments are omitted.

[0335]

[0336] <Absorption Spectroscopy>

[0337] Figure 18A and Figure 18BThe UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(dppm)2(acac)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.). The dichloromethane solution (0.093 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0338] <Emission Spectrum>

[0339] also, Figure 18A and Figure 18B The emission spectra of the thin film of 2mDBTPDBq-II as the first organic compound are shown (emission spectrum 7), the emission spectrum of the thin film of PCBA1BP as the second organic compound is shown (emission spectrum 8), and the emission spectrum of the thin film of a mixture of 2mDBTPDBq-II and PCBA1BP is shown (emission spectrum 9). Figure 18A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents the molar absorptivity ε (λ). ) and luminous intensity (any unit). In Figure 18B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0340] from Figure 18A The absorption spectrum shows that [Ir(dppm)2(acac)] has a broad absorption band around 520 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0341] Compared to emission spectra 7 and 8, the peak of emission spectrum 9 is located on the longer wavelength (lower energy) side. Furthermore, the peak of emission spectrum 9 is located closer to the absorption band compared to the peaks of emission spectra 7 and 8. Figure 18A and Figure 18B It can be seen that the emission spectrum with the greatest overlap with the absorption band that contributes significantly to luminescence in the absorption spectrum is emission spectrum 9. Specifically, the difference between the peak value (515 nm) of this absorption band in the absorption spectrum and the peak value of emission spectrum 9 is 0.02 eV.

[0342] Compared to the emission spectrum of the monomer, the emission spectrum of the mixture of 2mDBTPDBq-II and PCBA1BP has a peak at a longer wavelength (lower energy). This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and PCBA1BP.

[0343] The peak of the emission spectrum of this hybrid material overlaps significantly with the absorption band of [Ir(dppm)2(acac)], which is considered to contribute greatly to luminescence. Therefore, since the luminescent element using the hybrid material of 2mDBTPDBq-II and PCBA1BP and [Ir(dppm)2(acac)] utilizes the overlap between the emission spectrum of this hybrid material and the absorption spectrum of the phosphorescent compound to transfer energy, the energy transfer efficiency is high. This demonstrates that a luminescent element with high external quantum efficiency can be obtained.

[0344] [Example 6]

[0345] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0346] The following describes a method for manufacturing the light-emitting element 4 in this embodiment.

[0347] (Light-emitting element 4)

[0348] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0349] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0350] Then, the substrate is placed inside and depressurized to 10. -4 The substrate 1100 is placed in a vacuum evaporation apparatus at approximately Pa and then vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, followed by cooling for approximately 30 minutes.

[0351] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4 The hole injection layer 1111 is formed by co-depositing BPAFLP and molybdenum oxide (VI) on the first electrode 1101 at a thickness of approximately 40 nm. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of BPAFLP to molybdenum oxide is adjusted to 4:2 (=BPAFLP:molybdenum oxide).

[0352] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0353] Furthermore, a light-emitting layer 1113 is formed on the hole transport layer 1112 by co-depositing 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)2(acac)]. Here, the weight ratio of 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)2(acac)] is adjusted to 0.8:0.2:0.1 (=2mDBTPDBq-II: PCBA1BP:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40nm.

[0354] Next, a 2mDBTPDBq-II film with a thickness of 15nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0355] Next, a BPhen film with a thickness of 15 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0356] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0357] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 4 of this embodiment.

[0358] Note that resistance heating was used for evaporation in all of the above processes.

[0359] Table 5 shows the element structure of the light-emitting element 4 obtained through the above steps.

[0360] [Table 5]

[0361]

[0362] The light-emitting element 4 was sealed in a glove box under a nitrogen atmosphere to prevent it from being exposed to the atmosphere, and then the operating characteristics of the light-emitting element were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0363] Figure 19 The current density-luminance characteristics of the light-emitting element 4 are shown. Figure 19 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 20 The voltage-brightness characteristics are shown. Figure 20 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 21 The brightness-current efficiency characteristics are shown. Figure 21 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 22 The brightness-external quantum efficiency characteristics are shown. Figure 22 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0364] Furthermore, Table 6 shows the light-emitting element 4 at a brightness of 1100 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0365] [Table 6]

[0366]

[0367] Figure 23 The emission spectrum is shown when a current of 0.1 mA is applied to the light-emitting element 4. Figure 23 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 6, 1100 cd / m 2 The CIE color coordinates of the light-emitting element 4 at the specified brightness are (x, y) = (0.57, 0.43). From the above results, it can be seen that the light-emitting element 4 displays orange light originating from [Ir(dppm)2(acac)].

[0368] From Table 6 and Figures 19 to 22 It can be seen that the light-emitting element 4 has relatively high current efficiency, power efficiency, and external quantum efficiency. In particular, it has an efficiency of 1100 cd / m². 2 At the desired brightness, the external quantum efficiency of the light-emitting element 4 is extremely high, at 31%. As mentioned above, the upper limit of the external quantum efficiency is considered to be around 25%. However, this result exceeds that limit.

[0369] In the light-emitting element of this embodiment, 2mDBTPDBq-II, PCBA1BP, and [Ir(dppm)2(acac)] shown in Example 5 are used as the light-emitting layer. As can be seen from Example 5, compared to the emission spectra of the individual 2mDBTPDBq-II or PCBA1BP monomers, the emission spectrum of the mixed material of 2mDBTPDBq-II and PCBA1BP (the emission spectrum of the excitocomplex) overlaps significantly with the absorption spectrum of [Ir(dppm)2(acac)]. Since the light-emitting element of this embodiment utilizes this overlap for energy transfer, it can be considered to have high energy transfer efficiency, achieving a previously unrealized high external quantum efficiency.

[0370] In the results of Example 5, the peak value of the absorption band on the longest wavelength side of the absorption spectrum of the guest material used for the light-emitting element 4 is close to the peak value of the emission spectrum, and the molar absorptivity of the peak value is relatively large (>5000 M). -1 ·cm -1 As can be seen from the above results, the light-emitting element 4 has a high external quantum efficiency that has never been achieved before due to its particularly high energy transfer efficiency.

[0371] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0372] Next, a reliability test was conducted on the light-emitting element 4. Figure 24 The results of the reliability test are shown. Figure 24 In the diagram, the vertical axis represents the normalized brightness (%) with the initial brightness set to 100%, while the horizontal axis represents the driving time (h) of the element.

[0373] In reliability testing, the initial brightness was set to 5000 cd / m². 2 And it drives the light-emitting element 4 under the condition of constant current density.

[0374] The light-emitting element 4 retains 95% of its initial brightness after being driven for 170 hours.

[0375] As can be seen from the above results, a highly reliable component can be achieved by applying one aspect of the present invention.

[0376] [Example 7]

[0377] In this embodiment, refer to Figure 26A and Figure 26B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0378] The phosphorescent compound used in this embodiment is [Ir(dppm)2(acac)]. The first organic compound used in this embodiment is 2mDBTPDBq-II. The second organic compound used in this embodiment is 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB). The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in the above embodiments are omitted.

[0379]

[0380] <Absorption Spectroscopy>

[0381] Figure 26A and Figure 26B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(dppm)2(acac)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.). The dichloromethane solution (0.093 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0382] <Emission Spectrum>

[0383] also, Figure 26A and Figure 26B The emission spectra of a thin film of 2mDBTPDBq-II as the first organic compound are shown (emission spectrum 10), and the emission spectra of a thin film of a mixture of 2mDBTPDBq-II and NPB are shown (emission spectrum 11). Figure 26A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 26B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0384] from Figure 26A The absorption spectrum shows that [Ir(dppm)2(acac)] has a broad absorption band around 520 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0385] Compared to emission spectrum 10, the peak of emission spectrum 11 is located on the longer wavelength (lower energy) side. Furthermore, the peak of emission spectrum 11 is closer to the absorption band than the peak of emission spectrum 10. Additionally, the peak of the emission spectrum of NPB, the second organic compound, is known to be around 430 nm. Therefore, compared to the emission spectrum of NPB, the peak of emission spectrum 11 is located on the longer wavelength (lower energy) side. Moreover, the peak of emission spectrum 11 is closer to the absorption band than the peak of the emission spectrum of NPB. From the above results, it can be seen that emission spectrum 11 has the largest overlap with the absorption band in the absorption spectrum that contributes significantly to luminescence. Specifically, the difference between the peak of this absorption band (515 nm) in the absorption spectrum and the peak of emission spectrum 11 is 0.09 eV.

[0386] Compared to the emission spectrum of the monomer, the emission spectrum of the mixture of 2mDBTPDBq-II and NPB has a peak at a longer wavelength (lower energy). This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and NPB.

[0387] The peak value of the emission spectrum of this hybrid material overlaps significantly with the absorption band in the absorption spectrum of [Ir(dppm)2(acac)], which is considered to contribute greatly to luminescence. Therefore, since the luminescent element using the hybrid material of 2mDBTPDBq-II and NPB and [Ir(dppm)2(acac)] utilizes the overlap between the emission spectrum of this hybrid material and the absorption spectrum of the phosphorescent compound to transfer energy, the energy transfer efficiency is high. Thus, a luminescent element with high external quantum efficiency can be obtained.

[0388] [Example 8]

[0389] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. The chemical formulas of the materials used in this embodiment are shown below. Additionally, the chemical formulas of the materials used in the above embodiments are omitted.

[0390]

[0391] The following shows the manufacturing methods of the light-emitting element 5 and the comparative light-emitting element 6 in this embodiment.

[0392] (Light-emitting element 5)

[0393] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0394] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0395] Then, the substrate is placed inside and depressurized to 10. -4 The substrate 1100 is placed in a vacuum evaporation apparatus at approximately Pa and then vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, followed by cooling for approximately 30 minutes.

[0396] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4 At approximately Pa, 4,4',4''-(1,3,5-phenyltriyl)tris(dibenzothiophene) (abbreviation: DBT3P-II) and molybdenum oxide (VI) are co-deposited on the first electrode 1101 to form a hole injection layer 1111. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide is adjusted to 4:2 (=DBT3P-II:molybdenum oxide).

[0397] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0398] Furthermore, a light-emitting layer 1113 is formed on the hole transport layer 1112 by co-depositing 2mDBTPDBq-II, NPB, and [Ir(dppm)2(acac)]. Here, the weight ratio of 2mDBTPDBq-II, NPB, and [Ir(dppm)2(acac)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II:NPB:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40 nm.

[0399] Next, a 2mDBTPDBq-II film with a thickness of 10nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0400] Next, a BPhen film with a thickness of 20 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0401] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0402] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 5 of this embodiment.

[0403] (Compare with light-emitting element 6)

[0404] The light-emitting layer 1113 of the contrast light-emitting element 6 is formed by co-depositing 2mDBTPDBq-II and [Ir(dppm)2(acac)]. Here, the weight ratio of 2mDBTPDBq-II and [Ir(dppm)2(acac)] is adjusted to 1:0.05 (=2mDBTPDBq-II:[Ir(dppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40nm. Except for the light-emitting layer 1113, it is manufactured in the same way as the light-emitting element 5.

[0405] Note that resistance heating was used for evaporation in all of the above processes.

[0406] Table 7 shows the element structures of the light-emitting element 5 and the comparative light-emitting element 6 obtained through the above steps.

[0407] [Table 7]

[0408]

[0409] In a glove box under a nitrogen atmosphere, light-emitting element 5 and contrast light-emitting element 6 were sealed in a manner that prevented them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0410] Figure 27 The current density-brightness characteristics of light-emitting element 5 and contrasting light-emitting element 6 are shown. Figure 27 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 28 The voltage-brightness characteristics are shown. Figure 28 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 29 The brightness-current efficiency characteristics are shown. Figure 29 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 30 The brightness-external quantum efficiency characteristics are shown. Figure 30 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0411] Furthermore, Table 8 shows the brightness of light-emitting element 5 and contrasting light-emitting element 6 at approximately 1000 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0412] [Table 8]

[0413]

[0414] Figure 31 The emission spectra obtained when a current of 0.1 mA is applied to the light-emitting element 5 and the contrast light-emitting element 6 are shown. Figure 31 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 8, 1100 cd / m 2 The CIE color coordinates of the light-emitting element 5 at the specified brightness are (x, y) = (0.57, 0.43), 830 cd / m². 2 The CIE color coordinates of the contrasting light-emitting element 6 at the specified brightness are (x, y) = (0.56, 0.44). From the above results, it can be seen that both the light-emitting element 5 and the contrasting light-emitting element 6 display orange light originating from [Ir(dppm)2(acac)].

[0415] From Table 8 and Figures 27 to 30 It can be seen that the current efficiency, power efficiency and external quantum efficiency of the light-emitting element 5 are higher than those of the light-emitting element 6.

[0416] In the light-emitting element 5, 2mDBTPDBq-II, NPB, and [Ir(dppm)2(acac)] shown in Example 7 are used as the light-emitting layer. As can be seen from Example 7, compared to the emission spectrum of the 2mDBTPDBq-II monomer, the emission spectrum of the mixture of 2mDBTPDBq-II and NPB (the emission spectrum of the excitocomplex) overlaps significantly with the absorption band in the absorption spectrum of [Ir(dppm)2(acac)] that contributes greatly to luminescence. Since the light-emitting element 5 utilizes this overlap for energy transfer, its energy transfer efficiency is considered high, and therefore, its external quantum efficiency is higher than that of the comparative light-emitting element 6.

[0417] In the results of Example 7, the absorption band peak on the longest wavelength side of the absorption spectrum of the phosphorescent compound used in the light-emitting element 5 is close to the peak of the emission spectrum, and the molar absorptivity of the peak is relatively large (>5000 M). -1 ·cm -1 As can be seen from the above results, the light-emitting element 5 has a high external quantum efficiency that has never been achieved before due to its particularly high energy transfer efficiency.

[0418] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0419] [Example 9]

[0420] In this embodiment, refer to Figure 32A and Figure 32B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0421] The phosphorescent compound used in this embodiment is bis(2,3,5-triphenylpyrazine)(dineopentaylmethane)iridium(III) (abbreviated: [Ir(tppr)2(dpm)]). The first organic compound used in this embodiment is 2mDBTPDBq-II. The second organic compound used in this embodiment is NPB. The chemical formulas of the materials used in this embodiment are shown below. Additionally, the chemical formulas of the materials used in the above embodiments are omitted.

[0422]

[0423] <Absorption Spectroscopy>

[0424] Figure 32A and Figure 32B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(tppr)2(dpm)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.), with the dichloromethane solution (0.094 mmol / L) placed in a quartz dish and measured at room temperature.

[0425] <Emission Spectrum>

[0426] also, Figure 32A and Figure 32B The emission spectra of the thin film of 2mDBTPDBq-II as the first organic compound are shown (emission spectrum 12), and the emission spectra of the thin film of the mixture of 2mDBTPDBq-II and NPB are shown (emission spectrum 13). Figure 32A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 32B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0427] from Figure 32A The absorption spectrum shows that [Ir(tppr)2(dpm)] has a broad absorption band around 530 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0428] Compared to emission spectrum 12, the peak of emission spectrum 13 is located on the longer wavelength (lower energy) side. Furthermore, the peak of emission spectrum 13 is closer to the absorption band than the peak of emission spectrum 12. It is known that the peak of the emission spectrum of NPB, the second organic compound, is located around 430 nm. Therefore, compared to the emission spectrum of NPB, the peak of emission spectrum 13 is located on the longer wavelength (lower energy) side. Moreover, the peak of emission spectrum 13 is closer to the absorption band than the peak of the emission spectrum of NPB. From the above results, it can be seen that emission spectrum 13 has the largest overlap with the absorption band in the absorption spectrum that contributes significantly to luminescence. Specifically, the difference between the peak of this absorption band in the absorption spectrum (the shoulder peak around 530 nm) and the peak of emission spectrum 13 is 0.01 eV.

[0429] Compared to the emission spectrum of the monomer, the emission spectrum of the mixture of 2mDBTPDBq-II and NPB has a peak at a longer wavelength (lower energy). This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and NPB.

[0430] The peak value of the emission spectrum of this hybrid material overlaps significantly with the absorption band in the absorption spectrum of [Ir(tppr)2(dpm)], which is considered to contribute greatly to luminescence. Therefore, since the luminescent element using the hybrid material of 2mDBTPDBq-II and NPB and [Ir(tppr)2(dpm)] utilizes the overlap between the emission spectrum of this hybrid material and the absorption spectrum of the phosphorescent compound to transfer energy, the energy transfer efficiency is high. Thus, a luminescent element with high external quantum efficiency can be obtained.

[0431] [Example 10]

[0432] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0433] The following shows the manufacturing methods of the light-emitting element 7 and the comparative light-emitting element 8 in this embodiment.

[0434] (Light-emitting element 7)

[0435] The light-emitting layer 1113 of the light-emitting element 7 is formed by co-depositing 2mDBTPDBq-II, NPB, and [Ir(tppr)2(dpm)]. Here, the weight ratio of 2mDBTPDBq-II, NPB, and [Ir(tppr)2(dpm)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II:NPB:[Ir(tppr)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 40nm. Except for the light-emitting layer 1113, it is manufactured in the same manner as the light-emitting element 5 shown in Example 8.

[0436] (Compare with light-emitting element 8)

[0437] The light-emitting layer 1113 of the comparative light-emitting element 8 is formed by co-depositing 2mDBTPDBq-II and [Ir(tppr)2(dpm)]. Here, the weight ratio of 2mDBTPDBq-II and [Ir(tppr)2(dpm)] is adjusted to 1:0.05 (=2mDBTPDBq-II:[Ir(tppr)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 40nm. Except for the light-emitting layer 1113, it is manufactured in the same manner as the light-emitting element 5 shown in Example 8.

[0438] Table 9 shows the element structures of the light-emitting element 7 and the comparative light-emitting element 8 obtained through the above steps.

[0439] [Table 9]

[0440]

[0441] In a glove box under a nitrogen atmosphere, the light-emitting element 7 and the control light-emitting element 8 were sealed in a manner that prevented them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0442] Figure 33 The current density-luminance characteristics of light-emitting element 7 and contrasting light-emitting element 8 are shown. Figure 33 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 34 The voltage-brightness characteristics are shown. Figure 34 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 35 The brightness-current efficiency characteristics are shown. Figure 35 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 36The brightness-external quantum efficiency characteristics are shown. Figure 36 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0443] Furthermore, Table 10 shows the brightness of light-emitting element 7 and contrasting light-emitting element 8 at approximately 1000 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0444] [Table 10]

[0445]

[0446] Figure 37 The emission spectra obtained when a current of 0.1 mA is applied to the light-emitting element 7 and the contrast light-emitting element 8 are shown. Figure 37 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). Additionally, as shown in Table 10, 1100 cd / m 2 The CIE color coordinates of the light-emitting element 7 at a brightness of 1000 cd / m² are (x, y) = (0.66, 0.34). 2 The CIE color coordinates of the contrast emitting element 8 at the specified brightness are (x, y) = (0.66, 0.34). From the above results, it can be seen that the emitting element 7 and the contrast emitting element 8 display red light originating from [Ir(tppr)2(dpm)].

[0447] From Table 10 and Figures 33 to 36 It can be seen that the current efficiency, power efficiency and external quantum efficiency of the light-emitting element 7 are higher than those of the light-emitting element 8.

[0448] In the light-emitting element 7, 2mDBTPDBq-II, NPB, and [Ir(tppr)2(dpm)] shown in Example 9 are used as the light-emitting layer. As can be seen from Example 9, compared to the emission spectrum of the 2mDBTPDBq-II monomer, the emission spectrum (emission spectrum of the excitocomplex) of the mixed material of 2mDBTPDBq-II and NPB overlaps significantly with the absorption bands in the absorption spectrum of [Ir(tppr)2(dpm)] that are considered to contribute greatly to luminescence. Since the light-emitting element 7 utilizes this overlap for energy transfer, its energy transfer efficiency is considered high, and therefore, its external quantum efficiency is higher than that of the comparative light-emitting element 8.

[0449] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0450] Next, reliability tests were conducted on the light-emitting element 7 and the comparative light-emitting element 8. Figure 38 The results of the reliability test are shown. Figure 38 In the diagram, the vertical axis represents the normalized brightness (%) with the initial brightness set to 100%, while the horizontal axis represents the driving time (h) of the element.

[0451] In reliability testing, the initial brightness was set to 5000 cd / m². 2 And under the condition of constant current density, it drives the light-emitting element 7 and the contrast light-emitting element 8.

[0452] After 97 hours, the brightness of light-emitting element 8 was 63% of its initial brightness. After 98 hours, the brightness of light-emitting element 7 was 87% of its initial brightness. These results indicate that the lifespan of light-emitting element 7 is longer than that of light-emitting element 8.

[0453] As can be seen from the above results, a highly reliable component can be achieved by applying one aspect of the present invention.

[0454] [Example 11]

[0455] In this embodiment, refer to Figure 39A and Figure 39B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0456] The phosphorescent compound used in this embodiment is (acetylacetonate)bis(6-methyl-4-phenylpyrimidinium)iridium(III) (abbreviation: [Ir(mppm)2(acac)]). The first organic compound used in this embodiment is 2mDBTPDBq-II. The two second organic compounds used in this embodiment are PCBA1BP and 4-(1-naphthyl)-4'-phenyltriphenylamine (abbreviation: αNBA1BP). The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in the above embodiments are omitted.

[0457]

[0458] <Absorption Spectroscopy>

[0459] Figure 39A and Figure 39B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(mppm)2(acac)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.). The dichloromethane solution (0.10 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0460] <Emission Spectrum>

[0461] also, Figure 39A and Figure 39B The emission spectra of the film containing 2mDBTPDBq-II as the first organic compound (emission spectrum 14), the emission spectra of the film containing PCBA1BP as the second organic compound (emission spectrum 15), the emission spectra of the film containing αNBA1BP as the second organic compound (emission spectrum 16), the emission spectra of the film containing a mixture of 2mDBTPDBq-II and PCBA1BP (emission spectrum 17), and the emission spectrum of the film containing a mixture of 2mDBTPDBq-II and αNBA1BP (emission spectrum 18) are shown. Figure 39A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 39B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0462] from Figure 39A The absorption spectrum shows that [Ir(mppm)2(acac)] has a broad absorption band around 490 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0463] Compared to the emission spectra of the monomers, the peak values ​​of the emission spectra of the mixture of 2mDBTPDBq-II and PCBA1BP (emission spectrum 17) and the peak values ​​of the emission spectra of the mixture of 2mDBTPDBq-II and αNBA1BP (emission spectrum 18) are located on the longer wavelength (lower energy) side, respectively. This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and PCBA1BP. Furthermore, this also indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and αNBA1BP.

[0464] The peak value of the emission spectrum of the aforementioned mixed material overlaps significantly with the absorption band in the absorption spectrum of [Ir(mppm)2(acac)], which is considered to contribute greatly to luminescence. Therefore, luminescent elements using the mixed material of 2mDBTPDBq-II and PCBA1BP and [Ir(mppm)2(acac)], and luminescent elements using the mixed material of 2mDBTPDBq-II and αNBA1BP and [Ir(mppm)2(acac)], utilize the overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound to transfer energy, resulting in high energy transfer efficiency. Thus, luminescent elements with high external quantum efficiency can be obtained.

[0465] Compared to emission spectrum 17, the peak of emission spectrum 18 is located on the shorter wavelength (higher energy) side. Furthermore, the peak of emission spectrum 18 is located closer to the absorption band than the peak of emission spectrum 17. Specifically, the difference between the peak of the absorption band in the absorption spectrum (the shoulder peak near 490 nm) and the peak of emission spectrum 17 is 0.15 eV, and the difference between the peak of the absorption band in the absorption spectrum (the shoulder peak near 490 nm) and the peak of emission spectrum 18 is 0.01 eV.

[0466] The difference between the peak values ​​of emission spectrum 17 and emission spectrum 18 can be attributed to the difference between the HOMO energy levels of PCBA1BP and αNBA1BP. Specifically, the HOMO energy level of PCBA1BP is -5.43 eV, while that of αNBA1BP is -5.52 eV (these values ​​were calculated using cyclic voltammetry (CV)). The HOMO energy level of αNBA1BP is lower (deeper) than that of PCBA1BP, therefore, the peak value of emission spectrum 18 can be considered to be on the shorter wavelength (higher energy) side compared to emission spectrum 17.

[0467] [Example 12]

[0468] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0469] The following describes the manufacturing method of the light-emitting element 9 and the light-emitting element 10 in this embodiment.

[0470] (Light-emitting element 9)

[0471] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0472] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0473] Then, the substrate is placed inside and depressurized to 10. -4 The substrate 1100 is placed in a vacuum evaporation apparatus at approximately Pa and then vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, followed by cooling for approximately 30 minutes.

[0474] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4 The hole injection layer 1111 is formed by co-depositing BPAFLP and molybdenum oxide (VI) on the first electrode 1101 at a thickness of approximately 40 nm. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of BPAFLP to molybdenum oxide is adjusted to 4:2 (=BPAFLP:molybdenum oxide).

[0475] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0476] Furthermore, 2mDBTPDBq-II, PCBA1BP, and [Ir(mppm)2(acac)] are co-deposited on the hole transport layer 1112 to form a light-emitting layer 1113. Here, the weight ratio of 2mDBTPDBq-II, PCBA1BP, and [Ir(mppm)2(acac)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II: PCBA1BP:[Ir(mppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40nm.

[0477] Next, a 2mDBTPDBq-II film with a thickness of 10nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0478] Next, a BPhen film with a thickness of 20 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0479] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0480] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 9 of this embodiment.

[0481] (Light-emitting element 10)

[0482] The light-emitting layer 1113 of the light-emitting element 10 is formed by co-deposition of 2mDBTPDBq-II, αNBA1BP, and [Ir(mppm)2(acac)]. Here, the weight ratio of 2mDBTPDBq-II, αNBA1BP, and [Ir(mppm)2(acac)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II: αNBA1BP:[Ir(mppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40 nm. Except for the light-emitting layer 1113, it is manufactured in the same manner as the light-emitting element 9.

[0483] Note that resistance heating was used for evaporation in all of the above processes.

[0484] Table 11 shows the element structures of light-emitting element 9 and light-emitting element 10 obtained through the above steps.

[0485] [Table 11]

[0486]

[0487] Light-emitting elements 9 and 10 were sealed in a glove box under a nitrogen atmosphere to prevent them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0488] Figure 40 The current density-luminance characteristics of light-emitting elements 9 and 10 are shown. Figure 40 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 41 The voltage-brightness characteristics are shown. Figure 41 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 42 The brightness-current efficiency characteristics are shown. Figure 42 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 43 The brightness-external quantum efficiency characteristics are shown. Figure 43 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0489] Furthermore, Table 12 shows that light-emitting elements 9 and 10 have a brightness of approximately 1000 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0490] [Table 12]

[0491]

[0492] Figure 44 The emission spectra obtained when a current of 0.1 mA is applied to light-emitting elements 9 and 10 are shown. Figure 44 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 12, 1100 cd / m 2 The CIE color coordinates of the luminous element 9 at a brightness of 860 cd / m² are (x, y) = (0.43, 0.56). 2 The CIE color coordinates of the light-emitting element 10 at the specified brightness are (x, y) = (0.43, 0.56). From the above results, it can be seen that light-emitting elements 9 and 10 display yellow-green light originating from [Ir(mppm)2(acac)].

[0493] From Table 12 and Figures 40 to 43 It can be seen that the current efficiency, power efficiency and external quantum efficiency of light-emitting element 9 and light-emitting element 10 are relatively high.

[0494] In light-emitting elements 9 and 10, PCBA1BP or αNBA1BP, 2mDBTPDBq-II, and [Ir(mppm)2(acac)] shown in Example 11 are used as the light-emitting layer. As can be seen from Example 11, there is a large overlap between the emission spectrum (emission spectrum of the excitocomplex) of the mixed material of 2mDBTPDBq-II and PCBA1BP or αNBA1BP and the absorption spectrum of [Ir(mppm)2(acac)], where the absorption bands that can be considered to contribute significantly to luminescence are present. Since light-emitting elements 9 and 10 utilize this overlap for energy transfer, their energy transfer efficiency is considered high, and therefore their external quantum efficiency is high.

[0495] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0496] Next, reliability tests were conducted on light-emitting element 9 and light-emitting element 10. Figure 45 The results of the reliability test are shown. Figure 45In the diagram, the vertical axis represents the normalized brightness (%) with the initial brightness set to 100%, while the horizontal axis represents the driving time (h) of the element.

[0497] In reliability testing, the initial brightness was set to 5000 cd / m². 2 And under the condition of constant current density, it drives the light-emitting element 9 and the light-emitting element 10.

[0498] The brightness of light-emitting element 9 after 260 hours is 74% of its initial brightness. Furthermore, the brightness of light-emitting element 10 after 260 hours is 75% of its initial brightness. These results indicate that light-emitting elements 9 and 10 have relatively long lifespans.

[0499] As can be seen from the above results, a highly reliable component can be achieved by applying one aspect of the present invention.

[0500] [Example 13]

[0501] In this embodiment, refer to Figure 46A and Figure 46B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0502] The phosphorescent compound used in this embodiment is (acetylacetonate)bis(6-tert-butyl-4-phenylpyrimidinium)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]). The first organic compound used in this embodiment is 2mDBTPDBq-II. The two second organic compounds used in this embodiment are NPB and 2,7-bis[N-(diphenylaminophenyl)-N-phenylamino]-spirocyclic-9,9'-bifluorene (abbreviation: DPA2SF). The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in the above embodiments are omitted.

[0503]

[0504] <Absorption Spectroscopy>

[0505] Figure 46A and Figure 46B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(tBuppm)2(acac)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.), with the dichloromethane solution (0.093 mmol / L) placed in a quartz dish and measured at room temperature.

[0506] <Emission Spectrum>

[0507] also, Figure 46A and Figure 46B The emission spectra of the film containing 2mDBTPDBq-II as the first organic compound (emission spectrum 19), the emission spectra of the film containing DPA2SF as the second organic compound (emission spectrum 20), the emission spectra of the film containing a mixture of 2mDBTPDBq-II and DPA2SF (emission spectrum 21), and the emission spectra of the film containing a mixture of 2mDBTPDBq-II and NPB (emission spectrum 22) are shown. Figure 46A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 46B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0508] from Figure 46A The absorption spectrum shows that [Ir(tBuppm)2(acac)] has a broad absorption band around 490 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0509] Compared to the emission spectrum of the monomer, the emission spectrum (emission spectrum 21) of the mixture of 2mDBTPDBq-II and DPA2SF has a peak at a longer wavelength (lower energy). This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and DPA2SF.

[0510] The emission spectrum of NPB monomer is known to peak around 430 nm. From... Figure 46A It can be seen that since the peak of the emission spectrum (emission spectrum 22) of the mixed material of 2mDBTPDBq-II and NPB is located on the wavelength side longer than 430nm, an excitocomplex is formed by mixing 2mDBTPDBq-II and NPB.

[0511] The peak value of the emission spectrum of the aforementioned mixed material overlaps significantly with the absorption band in the absorption spectrum of [Ir(tBuppm)2(acac)], which is considered to contribute greatly to luminescence. Therefore, luminescent elements using a mixture of 2mDBTPDBq-II and DPA2SF with [Ir(tBuppm)2(acac)], and luminescent elements using a mixture of 2mDBTPDBq-II and NPB with [Ir(tBuppm)2(acac)], utilize the overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound to transfer energy, resulting in high energy transfer efficiency. Thus, luminescent elements with high external quantum efficiency can be obtained.

[0512] Compared to emission spectrum 21, the peak of emission spectrum 22 is located on the shorter wavelength (higher energy) side. Furthermore, the peak of emission spectrum 22 is located closer to the absorption band than the peak of emission spectrum 21. As described above, from Figure 46A and Figure 46B It can be seen that the emission spectrum with the greatest overlap with the absorption band that contributes significantly to luminescence in the absorption spectrum is emission spectrum 22. Specifically, the difference between the peak value of this absorption band in the absorption spectrum and the peak value of emission spectrum 21 is 0.39 eV, and the difference between the peak value of this absorption band in the absorption spectrum and the peak value of emission spectrum 22 is 0.19 eV.

[0513] The difference between the peak values ​​of emission spectrum 21 and emission spectrum 22 can be attributed to the difference between the HOMO energy levels of DPA2SF (used as the second organic compound) and NPB. Specifically, the HOMO energy level of DPA2SF is -5.09 eV, while that of NPB is -5.38 eV (these values ​​were calculated by cyclic voltammetry (CV)). Since the HOMO energy level of NPB is lower (deeper) than that of DPA2SF, the peak value of emission spectrum 22 can be considered to be located on the shorter wavelength (higher energy) side compared to emission spectrum 21.

[0514] As described above, compared to the light-emitting element using a mixture of 2mDBTPDBq-II and NPB and [Ir(tBuppm)2(acac)], the light-emitting element using a mixture of 2mDBTPDBq-II and DPA2SF and [Ir(tBuppm)2(acac)] transfers energy by utilizing the greater overlap between the emission spectrum of the mixture and the absorption spectrum of the phosphorescent compound, resulting in higher energy transfer efficiency. Therefore, a light-emitting element with higher external quantum efficiency can be obtained.

[0515] Furthermore, as can be seen from this embodiment, by changing only the second organic compound without changing the first organic compound, the overlap between the emission spectrum of the mixture of the first and second organic compounds and the absorption spectrum of the phosphorescent compound can be increased. In other words, by changing the emission color of the phosphorescent compound (the position of the absorption band in the absorption spectrum that contributes significantly to emission), only changing the second organic compound can yield a combination that increases this overlap, thereby obtaining a light-emitting element with high external quantum efficiency and long lifetime.

[0516] [Example 14]

[0517] In this embodiment, refer to Figure 15This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0518] The following describes the manufacturing method of the light-emitting element 11 and the light-emitting element 12 in this embodiment.

[0519] (Light-emitting element 11)

[0520] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0521] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0522] Then, the substrate is placed inside and depressurized to 10. -4 The substrate 1100 is placed in a vacuum evaporation apparatus at approximately Pa and then vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, followed by cooling for approximately 30 minutes.

[0523] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4 The hole injection layer 1111 is formed by co-depositing DBT3P-II and molybdenum oxide (VI) on the first electrode 1101 at a thickness of approximately 40 nm. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide is adjusted to 4:2 (=DBT3P-II:molybdenum oxide).

[0524] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0525] Furthermore, a light-emitting layer 1113 is formed on the hole transport layer 1112 by co-depositing 2mDBTPDBq-II, DPA2SF, and [Ir(tBuppm)2(acac)]. Here, the weight ratio of 2mDBTPDBq-II, DPA2SF, and [Ir(tBuppm)2(acac)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II: DPA2SF:[Ir(tBuppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40 nm.

[0526] Next, a 2mDBTPDBq-II film with a thickness of 10nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0527] Next, a BPhen film with a thickness of 20 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0528] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0529] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 11 of this embodiment.

[0530] (Light-emitting element 12)

[0531] The light-emitting layer 1113 of the light-emitting element 12 is formed by co-deposition of 2mDBTPDBq-II, NPB, and [Ir(tBuppm)2(acac)]. Here, the weight ratio of 2mDBTPDBq-II, NPB, and [Ir(tBuppm)2(acac)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II: NPB:Ir(tBuppm)2(acac)]). The thickness of the light-emitting layer 1113 is set to 40nm. Except for the light-emitting layer 1113, it is manufactured in the same manner as the light-emitting element 11.

[0532] Note that resistance heating was used for evaporation in all of the above processes.

[0533] Table 13 shows the element structures of light-emitting element 11 and light-emitting element 12 obtained through the above steps.

[0534] [Table 13]

[0535]

[0536] Light-emitting elements 11 and 12 were sealed in a glove box under a nitrogen atmosphere to prevent them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0537] Figure 47 The current density-luminance characteristics of light-emitting elements 11 and 12 are shown. Figure 47 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 48 The voltage-brightness characteristics are shown. Figure 48 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 49 The brightness-current efficiency characteristics are shown. Figure 49 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 50 The brightness-external quantum efficiency characteristics are shown. Figure 50 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0538] Furthermore, Table 14 shows that the light-emitting elements 11 and 12 have a brightness of approximately 1000 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0539] [Table 14]

[0540]

[0541] Figure 51 The emission spectra obtained when a current of 0.1 mA is applied to light-emitting elements 11 and 12 are shown. Figure 51 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 14, 890 cd / m 2 The CIE color coordinates of the light-emitting element 11 at a brightness of 820 cd / m² are (x, y) = (0.43, 0.56). 2 The CIE color coordinates of the light-emitting element 12 at the specified brightness are (x, y) = (0.42, 0.57). From the above results, it can be seen that light-emitting elements 11 and 12 display yellow-green light originating from [Ir(tBuppm)2(acac)].

[0542] From Table 14 and Figures 47 to 50 It can be seen that the current efficiency, power efficiency and external quantum efficiency of light-emitting element 11 and light-emitting element 12 are relatively high.

[0543] In light-emitting elements 11 and 12, DPA2SF or NPB, 2mDBTPDBq-II, and [Ir(tBuppm)2(acac)] as shown in Example 13 are used as the light-emitting layer. As can be seen from Example 13, the emission spectrum (emission spectrum of the excitocomplex) of the mixture of 2mDBTPDBq-II and DPA2SF or NPB overlaps significantly with the absorption band of [Ir(tBuppm)2(acac)], which is considered to contribute greatly to luminescence. Since light-emitting elements 11 and 12 utilize this overlap for energy transfer, their energy transfer efficiency is considered high, and their external quantum efficiency is also considered high. In particular, the emission spectrum of the mixture of 2mDBTPDBq-II and NPB overlaps more significantly with this absorption band compared to the emission spectrum of the mixture of 2mDBTPDBq-II and DPA2SF. Therefore, light-emitting element 12 can be considered to have higher energy transfer efficiency and higher external quantum efficiency compared to light-emitting element 11 due to the utilization of this larger overlap for energy transfer. Furthermore, referring to the results of Example 13, it can be seen that the difference between the energy value of the peak value of the emission spectrum of the excitocomplex and the energy value of the peak value of the absorption band on the lowest energy side of the absorption spectrum is preferably within 0.3 eV.

[0544] In this embodiment, a light-emitting element with higher external quantum efficiency can be obtained by changing only the second organic compound (using NPB instead of DPA2SF) without changing the first organic compound (equivalent to 2mDBTPDBq-II).

[0545] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0546] [Example 15]

[0547] In this embodiment, refer to Figure 52A and Figure 52B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0548] The phosphorescent compound used in this embodiment is [Ir(mppr-Me)2(dpm)]. The two first organic compounds used in this embodiment are 2mDBTPDBq-II and 2-[4-(dibenzothiophene-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: DBTBIm-II). The second organic compound used in this embodiment is 4,4',4''-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation: 1'-TNATA). The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in the above embodiments are omitted.

[0549]

[0550] <Absorption Spectroscopy>

[0551] Figure 52A and Figure 52B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(mppr-Me)2(dpm)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.). The dichloromethane solution (0.093 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0552] <Emission Spectrum>

[0553] also, Figure 52A and Figure 52B The emission spectra of the thin film of 2mDBTPDBq-II as the first organic compound are shown (emission spectrum 23), the emission spectrum of the thin film of DBTBIm-II as the first organic compound is shown (emission spectrum 24), the emission spectrum of the thin film of 1'-TNATA as the second organic compound is shown (emission spectrum 25), the emission spectrum of the thin film of the mixed material of 2mDBTPDBq-II and 1'-TNATA is shown (emission spectrum 26), and the emission spectrum of the thin film of the mixed material of DBTBIm-II and 1'-TNATA is shown (emission spectrum 27). Figure 52A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 52B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0554] from Figure 52A The absorption spectrum shows that [Ir(mppr-Me)2(dpm)] has a broad absorption band around 520 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0555] Compared to the emission spectra of the monomers, the peak values ​​of the emission spectra of the mixture of 2mDBTPDBq-II and 1'-TNATA (emission spectrum 26) and the peak values ​​of the emission spectra of the mixture of DBTBIm-II and 1'-TNATA (emission spectrum 27) are located on the longer wavelength (lower energy) side, respectively. This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and 1'-TNATA. Furthermore, an excitocomplex is formed by mixing DBTBIm-II and 1'-TNATA.

[0556] The peak value of the emission spectrum of the aforementioned mixed material overlaps significantly with the absorption band in the absorption spectrum of [Ir(mppr-Me)2(dpm)], which is considered to contribute greatly to luminescence. Therefore, luminescent elements using a mixture of 2mDBTPDBq-II and 1'-TNATA with [Ir(mppr-Me)2(dpm)], and luminescent elements using a mixture of DBTBIm-II and 1'-TNATA with [Ir(mppr-Me)2(dpm)], utilize the overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound to transfer energy, resulting in high energy transfer efficiency. Thus, luminescent elements with high external quantum efficiency can be obtained.

[0557] Compared to emission spectrum 26, the peak of emission spectrum 27 is located on the shorter wavelength (higher energy) side. Furthermore, the peak of emission spectrum 27 is located closer to the absorption band than the peak of emission spectrum 26. As described above, from Figure 52A and Figure 52B It can be seen that the emission spectrum that overlaps the most with the absorption band that contributes significantly to luminescence in the absorption spectrum is emission spectrum 27. Specifically, the difference between the peak value of the absorption spectrum of this absorption band (the shoulder peak near 520 nm) and the peak value of emission spectrum 26 is 0.35 eV, and the difference between the peak value of the absorption spectrum of this absorption band (the shoulder peak near 520 nm) and the peak value of emission spectrum 27 is 0.01 eV.

[0558] The difference between the peak values ​​of emission spectrum 26 and emission spectrum 27 can be attributed to the difference between the LUMO energy levels of 2mDBTPDBq-II and DBTBIm-II, which are used as the first organic compound. Specifically, the LUMO energy level of 2mDBTPDBq-II is -2.95 eV, while that of DBTBIm-II is -2.52 eV (these values ​​were calculated by cyclic voltammetry (CV)). Since the LUMO energy level of DBTBIm-II is higher (shallower) than that of 2mDBTPDBq-II, it is assumed that the peak value of the emission spectrum of the mixture of 2mDBTPDBq-II and 1'-TNATA, which has a high HOMO energy level, is not located at a very long wavelength (in other words, the peak value of emission spectrum 27 is located on the shorter wavelength side compared to emission spectrum 26).

[0559] As described above, compared to the light-emitting element using a mixture of DBTBIm-II and 1'-TNATA and [Ir(mppr-Me)2(dpm)], the light-emitting element using a mixture of 2mDBTPDBq-II and 1'-TNATA and [Ir(mppr-Me)2(dpm)] transfers energy by utilizing the greater overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound, resulting in higher energy transfer efficiency. Therefore, a light-emitting element with higher external quantum efficiency can be obtained.

[0560] Furthermore, as can be seen from this embodiment, by changing only the first organic compound without changing the second organic compound, the overlap between the emission spectrum of the mixture of the first and second organic compounds and the absorption spectrum of the phosphorescent compound can be increased. In other words, even if the emission color of the phosphorescent compound (the position of the absorption band that contributes significantly to emission in the absorption spectrum) is changed, a combination that increases the overlap can be obtained by changing only the first organic compound, thereby obtaining a light-emitting element with high external quantum efficiency and long lifetime.

[0561] [Example 16]

[0562] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0563] The following describes the manufacturing method of the light-emitting element 13 and the light-emitting element 14 in this embodiment.

[0564] (Light-emitting element 13)

[0565] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0566] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0567] Then, the substrate is placed inside and depressurized to 10. -4 The substrate 1100 is placed in a vacuum evaporation apparatus at approximately Pa and then vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, followed by cooling for approximately 30 minutes.

[0568] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4 The hole injection layer 1111 is formed by co-depositing BPAFLP and molybdenum oxide (VI) on the first electrode 1101 at a thickness of approximately 40 nm. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of BPAFLP to molybdenum oxide is adjusted to 4:2 (=BPAFLP:molybdenum oxide).

[0569] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0570] Furthermore, a light-emitting layer 1113 is formed on the hole transport layer 1112 by co-depositing 2mDBTPDBq-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)]. Here, the weight ratio of 2mDBTPDBq-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II: 1'-TNATA:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 20 nm.

[0571] Next, a 2mDBTPDBq-II film with a thickness of 30nm is formed on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0572] Next, a BPhen film with a thickness of 20 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0573] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0574] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 13 of this embodiment.

[0575] (Light-emitting element 14)

[0576] The light-emitting layer 1113 of the light-emitting element 14 is formed by co-evaporation of DBTBIm-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)]. Here, the weight ratio of DBTBIm-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)] is adjusted to 0.8:0.2:0.05 (=DBTBIm-II: 1'-TNATA:Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 20 nm.

[0577] The first electron transport layer 1114a of the light-emitting element 14 is formed using a DBTBIm-II film with a thickness of 30 nm. Except for the light-emitting layer 1113 and the first electron transport layer 1114a, it is manufactured in the same manner as the light-emitting element 13.

[0578] Note that resistance heating was used for evaporation in all of the above processes.

[0579] Table 15 shows the element structures of light-emitting element 13 and light-emitting element 14 obtained through the above steps.

[0580] [Table 15]

[0581]

[0582] Light-emitting elements 13 and 14 were sealed in a glove box under a nitrogen atmosphere to prevent them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0583] Figure 53 The current density-luminance characteristics of light-emitting elements 13 and 14 are shown. Figure 53 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 54 The voltage-brightness characteristics are shown. Figure 54 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 55The brightness-current efficiency characteristics are shown. Figure 55 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 56 The brightness-external quantum efficiency characteristics are shown. Figure 56 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0584] Furthermore, Table 16 shows the light-emitting elements 13 and 14 at a brightness of 860 cd / m². 2 Voltage (V), current density (mA / cm²) 2 ), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0585] [Table 16]

[0586]

[0587] Figure 57 The emission spectra obtained when a current of 0.1 mA is applied to light-emitting elements 13 and 14 are shown. Figure 57 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 16, 860 cd / m 2 The CIE color coordinates of light-emitting elements 13 and 14 at the specified brightness are (x, y) = (0.53, 0.46). From the above results, it can be seen that light-emitting elements 13 and 14 display orange light originating from [Ir(mppr-Me)2(dpm)].

[0588] From Table 16 and Figures 53 to 56 It can be seen that the current efficiency, power efficiency and external quantum efficiency of light-emitting element 13 and light-emitting element 14 are relatively high.

[0589] In light-emitting elements 13 and 14, 2mDBTPDBq-II or DBTBIm-II, 1'-TNATA, and [Ir(mppr-Me)2(dpm)] as shown in Example 15 are used as the light-emitting layer. As can be seen from Example 15, the emission spectrum (emission spectrum of the excitocomplex) of the mixed material of 2mDBTPDBq-II or DBTBIm-II and 1'-TNATA overlaps significantly with the absorption band of [Ir(mppr-Me)2(dpm)], which is considered to contribute greatly to luminescence. Since light-emitting elements 13 and 14 utilize this overlap for energy transfer, their energy transfer efficiency is considered high, and their external quantum efficiency is also high. In particular, the emission spectrum of the mixed material of DBTBIm-II and 1'-TNATA overlaps more significantly with this absorption band compared to the emission spectrum of the mixed material of 2mDBTPDBq-II and 1'-TNATA. Therefore, it can be considered that the light-emitting element 14 has a higher energy transfer efficiency and a higher external quantum efficiency compared to the light-emitting element 13 due to the utilization of this larger overlap transfer energy. Furthermore, as can be seen from the results of Reference Example 15, the difference between the energy value of the peak value of the emission spectrum of the excimer complex and the energy value of the peak value of the absorption band on the lowest energy side of the absorption spectrum is preferably within 0.3 eV.

[0590] In this embodiment, a light-emitting element with higher external quantum efficiency can be obtained by changing only the first organic compound (using DBTBIm-II instead of 2mDBTPDBq-II) without changing the second organic compound (corresponding to 1'-TNATA).

[0591] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0592] [Example 17]

[0593] In this embodiment, refer to Figure 58A and Figure 58B This illustrates an example of a combination of a first organic compound, a second organic compound, and a phosphorescent compound that can be applied to a light-emitting element in one aspect of the present invention.

[0594] The phosphorescent compound used in this embodiment is [Ir(mppr-Me)2(dpm)]. The first organic compound used in this embodiment is 2mDBTPDBq-II. The two second organic compounds used in this embodiment are PCCNBB and 9-phenyl-9H-3-(9-phenyl-9H-carbazole-3-yl)carbazole (abbreviation: PCCP). The chemical formulas of the materials used in this embodiment are shown below. The chemical formulas of the materials used in the above embodiments are omitted.

[0595]

[0596] <Absorption Spectroscopy>

[0597] Figure 58A and Figure 58B The UV-Vis absorption spectrum (hereinafter simply referred to as the absorption spectrum) of a dichloromethane solution containing [Ir(mppr-Me)2(dpm)] as a phosphorescent compound is shown. The absorption spectrum was measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.). The dichloromethane solution (0.093 mmol / L) was placed in a quartz dish and the measurement was performed at room temperature.

[0598] <Emission Spectrum>

[0599] also, Figure 58A and Figure 58B The emission spectra of the film containing 2mDBTPDBq-II as the first organic compound (emission spectrum 28), the emission spectra of the film containing PCCNBB as the second organic compound (emission spectrum 29), the emission spectra of the film containing PCCP as the second organic compound (emission spectrum 30), the emission spectra of the film containing a mixture of 2mDBTPDBq-II and PCCNBB (emission spectrum 31), and the emission spectra of the film containing a mixture of 2mDBTPDBq-II and PCCP (emission spectrum 32) are shown. Figure 58A In the diagram, the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit). In Figure 58B In the diagram, the horizontal axis represents energy (eV), and the vertical axis represents the molar absorptivity ε (M). -1 ·cm -1 ) and luminous intensity (any unit).

[0600] from Figure 58A The absorption spectrum shows that [Ir(mppr-Me)2(dpm)] has a broad absorption band around 500 nm. This absorption band can be considered to be a significant contributor to luminescence.

[0601] Compared to the emission spectra of the monomers, the peak values ​​of the emission spectra of the mixture of 2mDBTPDBq-II and PCCNBB (emission spectrum 31) and the peak values ​​of the emission spectra of the mixture of 2mDBTPDBq-II and PCCP (emission spectrum 32) are located on the longer wavelength (lower energy) side, respectively. This indicates that an excitocomplex is formed by mixing 2mDBTPDBq-II and PCCNBB. Furthermore, an excitocomplex is also formed by mixing 2mDBTPDBq-II and PCCP.

[0602] The peak value of the emission spectrum of the aforementioned mixed material overlaps significantly with the absorption band of [Ir(mppr-Me)2(dpm)], which is considered to contribute greatly to luminescence. Therefore, luminescent elements using a mixture of 2mDBTPDBq-II and PCCNBB with [Ir(mppr-Me)2(dpm)], and luminescent elements using a mixture of 2mDBTPDBq-II and PCCP with [Ir(mppr-Me)2(dpm)], utilize the overlap between the emission spectrum of the mixed material and the absorption spectrum of the phosphorescent compound to transfer energy, resulting in high energy transfer efficiency. Thus, luminescent elements with high external quantum efficiency can be obtained.

[0603] Furthermore, as can be seen from this embodiment, carbazole compounds can be used as one of the first and second organic compounds that form the excitocomplex, in addition to aromatic amine compounds.

[0604] [Example 18]

[0605] In this embodiment, refer to Figure 15 This invention describes a light-emitting element according to one aspect of the present invention. Since the materials used in this embodiment are the same as those used in the above embodiments, their chemical formulas are omitted.

[0606] The following describes the manufacturing method of the light-emitting element 15 and the light-emitting element 16 in this embodiment.

[0607] (Light-emitting element 15)

[0608] First, an ITSO film is formed on a glass substrate 1100 by sputtering, thereby forming a first electrode 1101 used as an anode. Furthermore, its thickness is set to 110 nm, and its electrode area is set to 2 mm × 2 mm.

[0609] Next, as a pretreatment for forming light-emitting elements on substrate 1100, the substrate surface is washed with water and calcined at 200°C for 1 hour, followed by UV ozone treatment for 370 seconds.

[0610] Then, the substrate is placed inside and depressurized to 10. -4 The substrate 1100 is placed in a vacuum evaporation apparatus at approximately Pa and then vacuum-calcined at 170°C for 30 minutes in the heating chamber of the vacuum evaporation apparatus, followed by cooling for approximately 30 minutes.

[0611] Next, the substrate 1100 on which the first electrode 1101 is formed is fixed on a substrate support inside the vacuum evaporation apparatus with the surface on which the first electrode 1101 is formed facing downwards, and the pressure inside the vacuum evaporation apparatus is reduced to 10. -4The hole injection layer 1111 is formed by co-depositing BPAFLP and molybdenum oxide (VI) on the first electrode 1101 at a thickness of approximately 40 nm. The thickness of the hole injection layer 1111 is set to 40 nm, and the weight ratio of BPAFLP to molybdenum oxide is adjusted to 4:2 (=BPAFLP:molybdenum oxide).

[0612] Next, a BPAFLP film with a thickness of 20 nm is formed on the hole injection layer 1111 to form the hole transport layer 1112.

[0613] Furthermore, 2mDBTPDBq-II, PCNBB, and [Ir(mppr-Me)2(dpm)] are co-deposited on the hole transport layer 1112 to form a light-emitting layer 1113. Here, the weight ratio of 2mDBTPDBq-II, PCNBB, and [Ir(mppr-Me)2(dpm)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II: PCNBB:[Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 20nm.

[0614] Next, 2mDBTPDBq-II, PCNBB, and [Ir(mppr-Me)2(dpm)] are co-deposited on the light-emitting layer 1113 to form a first electron transport layer 1114a. Here, the weight ratio of 2mDBTPDBq-II, PCNBB, and [Ir(mppr-Me)2(dpm)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II:PCNBB:[Ir(mppr-Me)2(dpm)]). Furthermore, the thickness of the first electron transport layer 1114a is set to 40nm.

[0615] Next, a BPhen film with a thickness of 10 nm is formed on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0616] Then, a LiF film with a thickness of 1 nm is deposited on the second electron transport layer 1114b to form the electron injection layer 1115.

[0617] Finally, an aluminum film with a thickness of 200 nm is formed by vapor deposition to serve as the second electrode 1103 used as the cathode, thereby manufacturing the light-emitting element 15 of this embodiment.

[0618] (Light-emitting element 16)

[0619] The light-emitting layer 1113 of the light-emitting element 16 is formed by co-depositing 2mDBTPDBq-II, PCCP, and [Ir(mppr-Me)2(dpm)]. Here, the weight ratio of 2mDBTPDBq-II, PCCP, and [Ir(mppr-Me)2(dpm)] is adjusted to 0.8:0.2:0.05 (=2mDBTPDBq-II:PCCP:Ir(mppr-Me)2(dpm)]). The thickness of the light-emitting layer 1113 is set to 20nm. Except for the light-emitting layer 1113, it is manufactured in the same manner as the light-emitting element 15.

[0620] Note that resistance heating was used for evaporation in all of the above processes.

[0621] Table 17 shows the element structures of light-emitting element 15 and light-emitting element 16 obtained through the above steps.

[0622] [Table 17]

[0623]

[0624] In a glove box under a nitrogen atmosphere, light-emitting elements 15 and 16 were sealed in a manner that prevented them from being exposed to the atmosphere, and then the operating characteristics of these light-emitting elements were measured. Furthermore, the measurements were performed at room temperature (in an atmosphere maintained at 25°C).

[0625] Figure 59 The current density-luminance characteristics of light-emitting elements 15 and 16 are shown. Figure 59 In the diagram, the horizontal axis represents the current density (mA / cm²). 2 The vertical axis represents brightness (cd / m²). 2 ). Figure 60 The voltage-brightness characteristics are shown. Figure 60 In the diagram, the horizontal axis represents voltage (V), and the vertical axis represents brightness (cd / m²). 2 ). Figure 61 The brightness-current efficiency characteristics are shown. Figure 61 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the current efficiency (cd / A), while the vertical axis represents the current efficiency (cd / A). Figure 62 The brightness-external quantum efficiency characteristics are shown. Figure 62 In the middle, the horizontal axis represents brightness (cd / m²). 2 The vertical axis represents the external quantum efficiency (%), while the vertical axis represents the external quantum efficiency (%).

[0626] Furthermore, Table 18 shows the light-emitting elements 15 and 16 at a brightness of 1200 cd / m². 2 Voltage (V), current density (mA / cm²) 2), CIE color coordinates (x, y), current efficiency (cd / A), power efficiency (lm / W), and external quantum efficiency (%).

[0627] [Table 18]

[0628]

[0629] Figure 63 The emission spectra obtained when a current of 0.1 mA is applied to light-emitting elements 15 and 16 are shown. Figure 63 In the table, the horizontal axis represents wavelength (nm), and the vertical axis represents luminous intensity (any unit). As shown in Table 18, 1200 cd / m 2 The CIE color coordinates of the light-emitting element 15 at a brightness of 1200 cd / m² are (x, y) = (0.54, 0.45). 2 The CIE color coordinates of the light-emitting element 16 at the specified brightness are (x, y) = (0.54, 0.46). From the above results, it can be seen that light-emitting elements 15 and 16 display orange light originating from [Ir(mppr-Me)2(dpm)].

[0630] From Table 18 and Figures 59 to 62 It can be seen that the light-emitting elements 15 and 16 have relatively high current efficiency, power efficiency, and external quantum efficiency.

[0631] In light-emitting elements 15 and 16, 2mDBTPDBq-II, PCNBB or PCCP, and [Ir(mppr-Me)2(dpm)] as shown in Example 17 are used as the light-emitting layer. As can be seen from Example 17, the emission spectrum (emission spectrum of the excitocomplex) of the mixture of 2mDBTPDBq-II and PCNBB or PCCP overlaps significantly with the absorption spectrum of [Ir(mppr-Me)2(dpm)], where the absorption bands that contribute greatly to luminescence overlap. Since light-emitting elements 15 and 16 utilize this overlap for energy transfer, they can be considered to have high energy transfer efficiency and high external quantum efficiency.

[0632] Furthermore, as can be seen from this embodiment, in addition to aromatic amine compounds (PCBNBB), carbazole compounds (PCCP) can also be used to form excitocomplexes, and light-emitting elements with high external quantum efficiency can be obtained.

[0633] As can be seen from the above results, a device with high external quantum efficiency can be realized by applying one aspect of the present invention.

[0634] (See Example 1 for reference)

[0635] The following shows the organometallic complex used in the above embodiments, namely (acetylacetonate)bis(4,6-diphenylpyrimidinium)iridium(III) (also known as: bis[2-(6-phenyl-4-pyrimidinyl-... N3)Phenyl- C] (2,4-pentanedione- 2 Examples of the synthesis of [Ir(dppm)2(acac)] are given below.

[0636]

[0637] <Step 1: Synthesis of 4,6-diphenylpyrimidine (abbreviation: Hdppm)>

[0638] First, in a recovery flask equipped with a reflux reflux tube, 5.02 g of 4,6-dichloropyrimidine, 8.29 g of phenylboronic acid, 7.19 g of sodium carbonate, 0.29 g of bis(triphenylphosphine)palladium(II) dichloride (abbreviation: Pd(PPh3)2Cl2), 20 mL of water, and 20 mL of acetonitrile were added, and the air in the flask was replaced with argon. The reaction vessel was heated by irradiating it with microwaves (2.45 GHz, 100 W) for 60 minutes. Next, 2.08 g of phenylboronic acid, 1.79 g of sodium carbonate, 0.070 g of Pd(PPh3)2Cl2, 5 mL of water, and 5 mL of acetonitrile were added to the flask, and the mixture was again heated by irradiating it with microwaves (2.45 GHz, 100 W) for 60 minutes. Then, water was added to the solution, and the organic layer was extracted with dichloromethane. The resulting extract was washed with water and dried with magnesium sulfate. After drying, the solution was filtered. The solvent of the solution was distilled off, and the residue was subsequently purified by silica gel column chromatography using dichloromethane as the developing solvent. The result was a pyrimidine derivative, Hdppm (yellowish-white powder, 38% yield). Note that a microwave synthesis apparatus (manufactured by CEM Corporation, Discover) was used for microwave irradiation. The synthetic scheme (a-1) for step 1 is shown below.

[0639]

[0640] <Step 2: Synthesis of di-μ-chloro-bis[bis(4,6-diphenylpyrimidinium)iridium(III)] (abbreviation: [Ir(dppm)2Cl]2)>

[0641] Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.10 g of Hdppm obtained in step 1 above, and 0.69 g of iridium chloride hydrate (IrCl3·H2O) were added to a recovery flask equipped with a reflux duct, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 100 W) for 1 hour to induce the reaction. The solvent was distilled off, and the resulting residue was filtered with ethanol and washed to obtain the binuclear complex [Ir(dppm)2Cl]2 (reddish-brown powder, 88% yield). The synthetic scheme (a-2) for step 2 is shown below.

[0642]

[0643] <Step 3: Synthesis of (acetylacetone)bis(4,6-diphenylpyrimidine)iridium(III) (abbreviation: [Ir(dppm)2(acac)])>

[0644] Furthermore, in a recovery flask equipped with a reflux reflux tube, 40 mL of 2-ethoxyethanol, 1.44 g of [Ir(dppm)₂Cl]₂ obtained in step 2 above, 0.30 g of acetylacetone, and 1.07 g of sodium carbonate were added, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 120 W) for 60 minutes to induce the reaction. The solvent was distilled off, and the resulting residue was dissolved in dichloromethane and filtered to remove insoluble substances. The resulting filtrate was washed with water and then with saturated brine, and dried over magnesium sulfate. After drying, the solution was filtered. The solvent of this solution was distilled off, and the resulting residue was purified by silica gel column chromatography using dichloromethane:ethyl acetate = 50:1 (v / v) as the developing solvent. Recrystallization was then performed with a mixed solvent of dichloromethane and hexane to give an orange powder (yield 32%) as the target compound. The synthetic scheme (a-3) for step 3 is shown below.

[0645]

[0646] The nuclear magnetic resonance spectrum of the orange powder obtained in step 3 above ( 1 The analytical results of H NMR are shown below. From the above results, it can be seen that the organometallic complex [Ir(dppm)2(acac)] was obtained.

[0647] 1 H NMR. δ(CDCl3):1.83(s,6H),5.29(s,1H),6.48(d,2H),6.80(t,2H),6.90(t,2H ),7.55-7.63(m,6H),7.77(d,2H),8.17(s,2H),8.24(d,4H),9.17(s,2H).

[0648] (See Example 2 for reference)

[0649] The following shows the organometallic complex used in the above embodiments, namely (acetylacetonate)bis(6-methyl-4-phenylpyrimidinium)iridium(III) (also known as: bis[2-(6-methyl-4-pyrimidinyl- N3)Phenyl- C] (2,4-pentanedione- 2 Examples of the synthesis of [Ir(mppm)2(acac)] are given below.

[0650]

[0651] <Step 1: Synthesis of 4-methyl-6-phenylpyrimidine (abbreviation: Hmppm)>

[0652] First, in a recovery flask equipped with a reflux reflux tube, 4.90 g of 4-chloro-6-methylpyrimidine, 4.80 g of phenylboronic acid, 4.03 g of sodium carbonate, 0.16 g of bis(triphenylphosphine)palladium(II) dichloride (abbreviation: Pd(PPh3)2Cl2), 20 mL of water, and 10 mL of acetonitrile were added, and the air in the flask was replaced with argon. The reaction vessel was heated by irradiating it with microwaves (2.45 GHz, 100 W) for 60 minutes. Next, 2.28 g of phenylboronic acid, 2.02 g of sodium carbonate, 0.082 g of Pd(PPh3)2Cl2, 5 mL of water, and 10 mL of acetonitrile were added to the flask, and the mixture was again heated by irradiating it with microwaves (2.45 GHz, 100 W) for 60 minutes. Then, water was added to the solution and the mixture was extracted with dichloromethane. The obtained extract was washed with saturated sodium carbonate aqueous solution, water, and then with saturated brine, and dried over magnesium sulfate. After drying, the solution was filtered. The solvent of the solution was distilled off, and the residue was then purified by silica gel column chromatography using dichloromethane:ethyl acetate = 9:1 (v / v) as the developing solvent. As a result, the pyrimidine derivative of the target compound, Hmppm (orange oil, 46% yield), was obtained. Note that a microwave synthesis apparatus (manufactured by CEM, Discover) was used for microwave irradiation. The synthetic scheme (b-1) of step 1 is shown below.

[0653]

[0654] <Step 2: Synthesis of di-μ-chloro-bis[bis(6-methyl-4-phenylpyrimidinium)iridium(III)] (abbreviation: [Ir(mppm)2Cl]2)>

[0655] Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.51 g of Hmppm obtained in step 1 above, and 1.26 g of iridium chloride hydrate (IrCl3·H2O) were added to a recovery flask equipped with a reflux duct, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 100 W) for 1 hour to induce the reaction. The solvent was distilled off, and the resulting residue was washed with ethanol and filtered to obtain the binuclear complex [Ir(mppm)2Cl]2 (dark green powder, 77% yield). The synthetic scheme (b-2) for step 2 is shown below.

[0656]

[0657] <Step 3: Synthesis of (acetylacetonate)bis(6-methyl-4-phenylpyrimidine)iridium(III) (abbreviation: [Ir(mppm)2(acac)])>

[0658] Furthermore, in a recovery flask equipped with a reflux reflux tube, 40 mL of 2-ethoxyethanol, 1.84 g of the binuclear complex [Ir(mppm)2Cl]2 obtained in step 2 above, 0.48 g of acetylacetone, and 1.73 g of sodium carbonate were added, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 120 W) for 60 minutes to induce the reaction. The solvent was distilled off, and the resulting residue was dissolved in dichloromethane and filtered to remove insoluble substances. The resulting filtrate was washed with water and then with saturated brine, and dried over magnesium sulfate. After drying, the solution was filtered. The solvent in the solution was distilled off, and the resulting residue was purified by silica gel column chromatography using dichloromethane:ethyl acetate = 4:1 (v / v) as the developing solvent. Recrystallization was then performed with a mixed solvent of dichloromethane and hexane to give a yellow powder (yield 22%) as the target compound. The synthetic scheme (b-3) for step 3 is shown below.

[0659]

[0660] The nuclear magnetic resonance spectrum of the yellow powder obtained in step 3 above ( 1 The analytical results of H NMR are shown below. From the above results, it can be seen that the organometallic complex [Ir(mppm)2(acac)] was obtained.

[0661] 1H NMR. δ(CDCl3):1.78(s,6H),2.81(s,6H),5.24(s,1H),6.37(d,2H),6.77(t,2H),6.85(t,2H),7.61-7.63(m,4H),8.97(s,2H).

[0662] (See Example 3 for reference)

[0663] The following shows the organometallic complex used in the above embodiments, namely (acetylacetonate)bis(6-tert-butyl-4-phenylpyrimidinium)iridium(III) (also known as: bis[2-(6-tert-butyl-4-pyrimidinium- N3)Phenyl- C] (2,4-pentanedione- 2 Examples of the synthesis of [Ir(tBuppm)2(acac)] are given below.

[0664]

[0665] <Step 1: Synthesis of 4-tert-butyl-6-phenylpyrimidine (abbreviation: HtBuppm)>

[0666] First, 22.5 g of 4,4-dimethyl-1-phenylpentane-1,3-dione and 50 g of formamide were placed in a recovery flask equipped with a reflux flask, and the air in the flask was replaced with nitrogen. The reaction vessel was heated to reflux the reaction solution for 5 hours. Then, the solution was injected with an aqueous sodium hydroxide solution, and the organic layer was extracted with dichloromethane. The obtained organic layer was washed with water and saturated brine and dried with magnesium sulfate. After drying, the solution was filtered. The solvent of the solution was distilled off, and the residue was subsequently purified by silica gel column chromatography using hexane:ethyl acetate = 10:1 (v / v) as the developing solvent. As a result, the pyrimidine derivative HtBuppm (colorless oily substance, 14% yield) was obtained. The synthetic scheme (c-1) of step 1 is shown below.

[0667]

[0668] <Step 2: Synthesis of di-μ-chloro-bis[bis(6-tert-butyl-4-phenylpyrimidinium)iridium(III)] (abbreviation: [Ir(tBuppm)2Cl]2)>

[0669] Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.49 g of HtBuppm obtained in step 1 above, and 1.04 g of iridium chloride hydrate (IrCl3·H2O) were added to a recovery flask equipped with a reflux tube, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 100 W) for 1 hour to induce the reaction. The solvent was distilled off, and the resulting residue was subsequently filtered with ethanol and washed to give the binuclear complex [Ir(tBuppm)2Cl]2 (yellow-green powder, 73% yield). The synthetic scheme (c-2) for step 2 is shown below.

[0670]

[0671] <Step 3: Synthesis of (acetylacetone)bis(6-tert-butyl-4-phenylpyrimidine)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)])>

[0672] Furthermore, 40 mL of 2-ethoxyethanol, 1.61 g of the binuclear complex [Ir(tBuppm)2Cl]2 obtained in step 2 above, 0.36 g of acetylacetone, and 1.27 g of sodium carbonate were placed in a recovery flask equipped with a reflux tube, and the air in the flask was replaced with argon. The mixture was then irradiated with microwaves (2.45 GHz, 120 W) for 60 minutes to induce a reaction. The solvent was distilled off, and the resulting residue was filtered with ethanol and washed with water and ethanol. The solid was dissolved in dichloromethane, and the mixture was filtered through a filter aid consisting of a layer of diatomaceous earth (Celite, manufactured by Wako Pure Chemical Industries, Ltd., catalog number: 531-16855), alumina, and diatomaceous earth in that order. The solvent was distilled off, and the resulting solid was recrystallized from a mixed solvent of dichloromethane and hexane to obtain a yellow powder (68% yield) as the target product. The synthesis scheme (c-3) for step 3 is shown below.

[0673]

[0674] The nuclear magnetic resonance spectrum of the yellow powder obtained in step 3 above ( 1 The analytical results of H NMR are shown below. From the above results, it can be seen that the organometallic complex [Ir(tBuppm)2(acac)] was obtained.

[0675] 1H NMR. δ(CDCl3):1.50(s,18H),1.79(s,6H),5.26(s,1H),6.33(d,2H),6.77(t,2H),6.85(t,2H),7.70(d,2H),7.76(s,2H),9.02(s,2H).

[0676] (See Example 4 for reference)

[0677] The following describes the synthesis method of 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) used in the above examples.

[0678]

[0679] <Synthesis of 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II)>

[0680] The synthetic scheme (d-1) for 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II) is shown below.

[0681]

[0682] First, in a 2L three-necked flask, 5.3 g (20 mmol) of 2-chlorodibenzo[f,h]quinoxaline, 6.1 g (20 mmol) of 3-(dibenzothiophene-4-yl)phenylboronic acid, 460 mg (0.4 mmol) of tetra(triphenylphosphine)palladium(O), 300 mL of toluene, 20 mL of ethanol, and 20 mL of 2M potassium carbonate aqueous solution were added. The mixture was degassed by stirring under reduced pressure, and the air in the three-necked flask was replaced with nitrogen. The mixture was stirred at 100°C for 7.5 hours under a nitrogen stream. After cooling to room temperature, the resulting mixture was filtered to obtain a white substance. The residue was washed successively with water and ethanol, and then dried. The resulting solid was dissolved in approximately 600 mL of hot toluene, and then filtered through diatomaceous earth and magnesium silicate (Florisil) to obtain a colorless and transparent filtrate. The filtrate was concentrated and purified by column chromatography using approximately 700 mL of silica gel. This chromatography used hot toluene as the developing solvent. Acetone and ethanol were added to the resulting solid, followed by ultrasonic irradiation. The resulting suspension was then filtered and the solid was dried to give 7.85 g of a white powder, with a yield of 80%.

[0683] The target compound is relatively soluble in hot toluene but readily precipitates upon cooling. Furthermore, it is poorly soluble in other organic solvents such as acetone and ethanol. Therefore, utilizing these varying solubilities, it can be synthesized in high yield using the simple method described above. Specifically, after the reaction is complete, the mixture is returned to room temperature, and the precipitated solid is collected by filtration, thereby easily removing most impurities. Moreover, column chromatography using hot toluene as the developing solvent allows for the easy purification of the precipitating compound.

[0684] 4.0 g of white powder was purified by gradient sublimation. Purification was performed by heating the white powder at 300 °C under conditions of 5.0 Pa and argon flow rate of 5 mL / min. After purification, 3.5 g of the target white powder was obtained, with a yield of 88%.

[0685] Using nuclear magnetic resonance spectroscopy ( 1 ¹H NMR confirmed that the compound was the target 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II).

[0686] The following shows the obtained substances 1 H NMR data.

[0687] 1 H NMR (CDCl3,300MHz): δ (ppm)=7.45-7.52(m,2H), 7.59-7.65(m,2H), 7.71-7.91(m,7H), 8.20-8.25(m,2H), 8.41(d,J=7.8Hz,1H), 8.65 (d,J=7.5Hz,2H), 8.77-8.78(m,1H), 9.23(dd,J=7.2Hz,1.5Hz,1H), 9.42(dd,J=7.8Hz,1.5Hz,1H), 9.48(s,1H).

[0688] Symbol Explanation

[0689] 102 EL layer

[0690] 103 First Electrode

[0691] 108 Second Electrode

[0692] 701 Hole Injection Layer

[0693] 702 Hole Transport Layer

[0694] 703 Emissive Layer

[0695] 704 Electron Transport Layer

[0696] 705 Electron Injection Layer

[0697] 706 Electron Injection Buffer Layer

[0698] 707 Electronic Relay Layer

[0699] 708 Composite Material Layer

[0700] 800 First EL Floor

[0701] 801 Second EL Layer

[0702] 803 Charge Generation Layer

[0703] 1100 substrate

[0704] 1101 First Electrode

[0705] 1103 Second Electrode

[0706] 1111 Hole Injection Layer

[0707] 1112 Hole transport layer

[0708] 1113 Emissive Layer

[0709] 1114a First Electron Transport Layer

[0710] 1114b Second Electron Transport Layer

[0711] 1115 Electron Injection Layer

[0712] This application is based on Japanese Patent Application No. 2011-031462, filed with the Japan Patent Office on February 16, 2011, the entire contents of which are incorporated herein by reference.

Claims

1. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and a guest material, wherein the first organic compound is a heteroaromatic compound, wherein the second organic compound is a carbazole compound, wherein the first organic compound and the second organic compound form an exciplex, wherein a peak of an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side in an absorption spectrum of the guest material wherein a difference between an energy value of the peak of the emission spectrum of the exciplex and an energy value of a peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less, and wherein the peak of the absorption band on the longest wavelength side in the absorption spectrum is between 490 nm and 530 nm.

2. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and a guest material, wherein the first organic compound is a heteroaromatic compound, wherein the second organic compound is a carbazole compound, wherein the first organic compound and the second organic compound form an exciplex, wherein a peak of an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side in an absorption spectrum of the guest material, wherein a difference between an energy value of the peak of the emission spectrum of the exciplex and an energy value of a peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less, and wherein the peak of the absorption band on the longest wavelength side in the absorption spectrum is between 490 nm and 530 nm.

3. The light-emitting element according to claim 1 or 2, wherein a triplet excitation energy level of the first organic compound and a triplet excitation energy level of the second organic compound are both higher than a triplet excitation energy level of the guest material.

4. The light-emitting element according to claim 3, wherein wherein the triplet excitation energy level of the first organic compound, the triplet excitation energy level of the second organic compound, and the triplet excitation energy level of the guest material are all calculated using a time-dependent density functional method.

5. The light-emitting element according to claim 1 or 2, wherein, wherein the absorption band on the longest wavelength side corresponds to a direct transition from a singlet ground state to a triplet excited state.

6. The light-emitting element according to claim 1 or 2, wherein wherein the carbazole compound comprises a carbazol-3-yl group.

7. The light-emitting element according to claim 1 or 2, wherein, wherein the emission spectrum of the exciplex is a fluorescence spectrum.

8. The light-emitting element according to claim 1 or 2, further comprising: wherein, a hole-transport layer between the first electrode and the light-emitting layer, wherein the hole-transport layer comprises an aromatic amine compound, and wherein the aromatic amine compound comprises a fluorene group.

9. An electronic device comprising the light-emitting element according to claim 1 or 2.

10. A lighting device comprising the light-emitting element according to claim 1 or 2. ​ ​ 11. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer comprising a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound form an exciplex by selection of the first organic compound and the second organic compound, and wherein an external quantum efficiency of the light-emitting element is greater than 25 %.

12. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

13. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

14. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

15. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

16. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, ​ ​ ​ ​ ​ ​ wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

17. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

18. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

19. A light-emitting element comprising: a first electrode; a light-emitting layer over the first electrode; and a second electrode over the light-emitting layer, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

20. A light-emitting element comprising: a first electrode; a hole injection layer over the first electrode; a light-emitting layer over the hole injection layer; and a second electrode over the light-emitting layer, wherein the hole injection layer includes an electron acceptor, wherein the light-emitting layer includes a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

21. A light-emitting element comprising: a first electrode; a hole injection layer over the first electrode; a light-emitting layer over the hole injection layer; and a second electrode over the light-emitting layer, wherein the hole injection layer includes an electron acceptor, wherein the light-emitting layer includes a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

22. A light-emitting element comprising: a first electrode; a hole injection layer over the first electrode; a light-emitting layer over the hole injection layer; and a second electrode over the light-emitting layer, wherein the hole injection layer includes an electron acceptor, wherein the light-emitting layer includes a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

23. A light-emitting element comprising: a first electrode; a hole injection layer over the first electrode; a light-emitting layer over the hole injection layer; and a second electrode over the light-emitting layer, wherein the hole injection layer includes an electron acceptor, wherein the light-emitting layer includes a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

24. A light-emitting element comprising: a first electrode; a hole injection layer over the first electrode; a light-emitting layer over the hole injection layer; and a second electrode over the light-emitting layer, wherein the hole injection layer includes an electron acceptor, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

25. A light-emitting element comprising: a first electrode; a hole-injection layer over the first electrode; a light-emitting layer over the hole-injection layer; and a second electrode over the light-emitting layer, wherein the hole-injection layer comprises an electron acceptor, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

26. A light-emitting element comprising: a first electrode; a hole-injection layer over the first electrode; a light-emitting layer over the hole-injection layer; and a second electrode over the light-emitting layer, wherein the hole-injection layer comprises an electron acceptor, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of an absorption spectrum of the iridium complex, and wherein a difference between a peak energy of the emission spectrum and a peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

27. A light-emitting element comprising: a first electrode; a hole-injection layer over the first electrode; a light-emitting layer over the hole-injection layer; and a second electrode over the light-emitting layer, wherein the hole-injection layer comprises an electron acceptor, wherein the light-emitting layer comprises a first organic compound, a second organic compound, and an iridium complex, wherein the first organic compound and the second organic compound form an exciplex, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex, wherein the emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of the absorption spectrum of the iridium complex, and wherein a difference between the highest peak energy of the emission spectrum and the peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

28. The light-emitting element according to any one of claims 12 to 27, wherein the peak of the absorption band on the longest wavelength side in the absorption spectrum is between 490 nm and 530 nm.

29. The light-emitting element according to any one of Claims 12 to 15 and 20 to 23, wherein the first organic compound includes a heterocyclic compound, and wherein the second organic compound includes a carbazole compound.

30. The light-emitting element according to any one of claims 12 to 27, wherein The molar absorption coefficient of the absorption band on the longest wavelength side in the absorption spectrum is 2000 The above.

31. The light-emitting element according to any one of claims 12 to 27, wherein the emission spectrum is a fluorescence spectrum.

32. The light-emitting element according to any one of claims 12, 16, 20, and 24, wherein a difference between the peak energy of the emission spectrum and the peak energy of the absorption band on the longest wavelength side in the absorption spectrum is 0.01 eV or less.

33. The light-emitting element according to any one of claims 20 to 27, wherein the hole injection layer further includes an aromatic amine compound.

34. The light-emitting element according to any one of claims 12 to 27, wherein further includes an electron transport layer between the light-emitting layer and the second electrode, wherein the electron transport layer includes a heteroaromatic compound.

35. The light-emitting element according to any one of claims 12 to 27, wherein further includes an electron injection layer between the light-emitting layer and the second electrode, wherein the electron injection layer includes any of an alkali metal, an alkaline earth metal, and an alloy of the alkali metal or the alkaline earth metal.

36. The light-emitting element according to any one of claims 12 to 27, wherein the second electrode includes any of an alkali metal, an alkaline earth metal, magnesium, a rare earth metal, aluminum, and silver.

37. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound are selected to form an exciplex, wherein the emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of the absorption spectrum of the phosphorescent compound, wherein one of the first organic compound and the second organic compound is a carbazole compound, and wherein the carbazole compound contains a carbazol-3-yl group.

38. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound are selected to form an exciplex, wherein the emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of the absorption spectrum of the phosphorescent compound, wherein one of the first organic compound and the second organic compound is a carbazole compound, wherein the carbazole compound includes a first carbazole ring and a second carbazole ring, and wherein the 3-position of the first carbazole ring is bonded to the 3-position of the second carbazole ring.

39. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound are selected to form an exciplex, wherein the emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side of the absorption spectrum of the phosphorescent compound, one of the first organic compound and the second organic compound is a carbazole compound, wherein the carbazole compound includes two carbazole rings.

40. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer including a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound are selected to form an exciplex, wherein an emission spectrum of the exciplex overlaps with an absorption band on a longest wavelength side in an absorption spectrum of the phosphorescent compound, wherein a peak wavelength of the absorption band on the longest wavelength side is in a range from 490 nm to 530 nm.

41. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer including a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound are selected to form an exciplex, wherein an absorption spectrum of the phosphorescent compound includes a first absorption peak and a second absorption peak, wherein the first absorption peak is on a longest wavelength side in the absorption spectrum of the phosphorescent compound, wherein the second absorption peak is on a shorter wavelength side than the first absorption peak in the absorption spectrum, wherein the second absorption peak is next to the first absorption peak, and wherein a peak of an emission spectrum of the exciplex is on a longer wavelength side than the second absorption peak.

42. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer including a phosphorescent compound, a first organic compound, and a second organic compound, wherein the first organic compound and the second organic compound are selected to form an exciplex, wherein an absorption spectrum of the phosphorescent compound includes a first absorption peak and a second absorption peak, wherein the first absorption peak is on a longest wavelength side in the absorption spectrum of the phosphorescent compound, wherein the second absorption peak is on a shorter wavelength side than the first absorption peak in the absorption spectrum, wherein the second absorption peak is next to the first absorption peak, a peak of an emission spectrum of the exciplex is closer to the first absorption peak than to the second absorption peak.

43. The light-emitting element according to any one of claims 37 to 39, wherein the first organic compound is a heterocyclic compound.

44. The light-emitting element according to any one of claims 37 to 42, further comprising: a hole-injection layer, wherein the hole-injection layer includes an aromatic amine compound and an electron acceptor.

45. The light-emitting element according to any one of claims 37 to 42, further comprising: a hole-transport layer, wherein the hole-transport layer includes an aromatic amine compound, and wherein the aromatic amine compound includes a fluorene group.

46. The light-emitting element according to any one of claims 37 to 42, wherein one of the electrodes includes ytterbium.

47. The light-emitting element according to any one of claims 37 to 39, wherein an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band on the longest wavelength side in the absorption spectrum are different by 0.2 eV or less.

48. The light-emitting element according to claim 47, wherein an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band on the longest wavelength side in the absorption spectrum are different by 0.1 eV or less.

49. The light-emitting element according to any one of claims 37 to 40, wherein The absorption band on the longest wavelength side is an absorption wavelength corresponding to a direct transition from a singlet ground state to a triplet excited state.

50. The light-emitting element according to any one of claims 37 to 40, wherein The triplet excited energy level of each of the first organic compound and the second organic compound is higher than the triplet excited energy level of the phosphorescent compound.

51. The light-emitting element according to any one of Claims 37 to 40, wherein one of the first organic compound and the second organic compound has a higher content than the other, and the phosphorescence spectrum of the one overlaps with an absorption band on the longest wavelength side in the absorption spectrum of the phosphorescent compound.

52. The light-emitting element according to claim 39, wherein The two carbazole rings are directly bonded to each other.

53. The light-emitting element according to claim 40, wherein The difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

54. The light-emitting element according to claim 53, wherein The difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

55. The light-emitting element according to claim 41 or 42, wherein The difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less.

56. The light-emitting element according to claim 55, wherein The difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.1 eV or less.

57. The light-emitting element according to claim 41 or 42, wherein The absorption band on the longest wavelength side is an absorption wavelength corresponding to a direct transition from a singlet ground state to a triplet excited state.

58. The light-emitting element according to Claim 41, wherein one of the first organic compound and the second organic compound has a higher content than the other, and the phosphorescence spectrum of the one overlaps with an absorption band on the longest wavelength side in the absorption spectrum of the phosphorescent compound.

59. The light-emitting element according to Claim 42, wherein one of the first organic compound and the second organic compound has a higher content than the other, and the phosphorescence spectrum of the one overlaps with an absorption band on the longest wavelength side in the absorption spectrum of the phosphorescent compound.

60. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer including an iridium complex, a first organic compound, and a second organic compound, wherein the first organic compound is a carbazole compound having a carbazol-3-yl group, wherein the second organic compound is a heteroaromatic compound, wherein the first organic compound and the second organic compound form an exciplex, and wherein a peak of an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side in an absorption spectrum of the iridium complex.

61. A light-emitting element comprising: a pair of electrodes; and a light-emitting layer between the pair of electrodes, the light-emitting layer including an iridium complex, a first organic compound, and a second organic compound, wherein the first organic compound is a carbazole compound having a 9-phenyl-carbazol-3-yl group, wherein the second organic compound is a heteroaromatic compound, wherein the first organic compound and the second organic compound form an exciplex, and wherein a peak of an emission spectrum of the exciplex overlaps with an absorption band on the longest wavelength side in an absorption spectrum of the iridium complex.

62. The light-emitting element according to claim 60 or 61, wherein the triplet excitation energy level of the first organic compound and the triplet excitation energy level of the second organic compound are both higher than the triplet excitation energy level of the iridium complex.

63. The light-emitting element according to claim 60, wherein the carbazole compound has another carbazole-3-yl group bonded to the carbazole-3-yl group.

64. The light-emitting element according to claim 61, wherein the carbazole compound has a carbazole-3-yl group bonded to the 9-phenyl-carbazol-3-yl group.

65. The light-emitting element according to claim 60 or 61, wherein the absorption band corresponds to a direct transition from a singlet ground state to a triplet excited state.

66. The light-emitting element according to claim 60 or 61, wherein a peak of the absorption band is in a range from 490 nm to 530 nm.

67. An electronic device comprising the light-emitting element according to claim 60 or 61.

68. A lighting device comprising the light-emitting element according to claim 60 or 61.

69. A host material for a light-emitting device, comprising: a first organic compound; and a second organic compound, wherein the first organic compound and the second organic compound are selected so that the first organic compound and the second organic compound can form an exciplex, and wherein a triplet excitation energy level of the exciplex and a singlet excitation energy level of the exciplex are substantially the same.

70. The host material according to claim 69, wherein a peak of a fluorescence spectrum of the exciplex has a longer wavelength than peaks of fluorescence spectra of the first organic compound and the second organic compound.

71. The host material according to claim 69, wherein a LUMO level of the exciplex is derived from a LUMO level of the second organic compound, and a HOMO level of the exciplex is derived from a HOMO level of the first organic compound.

72. The host material according to claim 69, wherein the first organic compound is a carbazole compound, and the second organic compound is a heteroaromatic compound.

73. A method for using a light-emitting element, comprising: forming an exciplex between a first organic compound and a second organic compound in a light-emitting layer; and transferring excitation energy from the exciplex to a phosphorescent compound in the light-emitting layer, wherein an emission spectrum of the exciplex overlaps with an absorption band on a longest wavelength side in an absorption spectrum of the phosphorescent compound, and wherein a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band on the longest wavelength side in the absorption spectrum is 0.2 eV or less. ​ ​

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