Light-emitting element, electronic equipment and lighting equipment

Abstract

Light-emitting element (101), comprising: a first electrode; a first layer above the first electrode, wherein the first layer contains a first organic compound with a hole transport property; a light-emitting layer (102) above the first layer, wherein the light-emitting layer contains the first organic compound, a second organic compound with an electron transport property and a compound with a light-emitting property; a second layer above the light-emitting layer (102), wherein the second layer contains the second organic compound; and a second electrode above the second layer, wherein the first organic compound and the second organic compound are chosen to form an exciplex, where a triplet excitation level of the first organic compound and a triplet excitation level of the second organic compound are higher than a triplet excitation level of the compound with a light-emitting property, wherein the compound is configured with a light-emitting property to convert energy of the triplet excitation level of the compound into light emission, and where the LUMO level of the compound with a light-emitting property is lower than the LUMO level of the first organic compound and the second organic compound.

Description

Technical field

[0001] The present invention relates to light-emitting elements which employ an organic electroluminescence (EL) phenomenon (hereinafter such light-emitting elements are also referred to as EL elements). State of the art

[0002] An organic EL element has been actively researched and developed. In the basic structure of an organic EL element, a layer containing a luminescent organic compound (hereinafter also referred to as a light-emitting layer) is positioned between a pair of electrodes. The organic EL element has attracted attention as a next-generation flat panel display due to its properties: it can be manufactured thinner and lighter, it has fast response times for signal input, and it can operate on low-voltage DC power. Additionally, a display using such a light-emitting element is characterized by excellent contrast and image quality, as well as a wide viewing angle.Furthermore, since it is a planar light source, attempts have been made to use the organic EL element as a light source, such as for backlighting a liquid crystal display and as a lighting device.

[0003] The emission mechanism of the organic EL cell is a carrier-injection type. This means that when a voltage is applied, electrons and holes injected by the electrodes recombine through a light-emitting layer located between the electrodes, exciting the light-emitting substance. Light is emitted when the excited state relaxes to the ground state. There are two types of excited states: a singlet state (S*) and a triplet state (T*). The ratio of the statistical generation of the excited states is given as S*:T* = 1:3.

[0004] In general, the ground state of a light-emitting organic compound is a singlet state. Therefore, light emission from the excited singlet state is called fluorescence, as it occurs through electron transfer between multiples of the same spin. On the other hand, light emission from the excited triplet state is called phosphorescence, in which electron transfer occurs between multiples of different spin. In a compound that emits fluorescence (hereafter referred to as a fluorescent compound), phosphorescence is generally not observed at room temperature, and only fluorescence is observed.Consequently, it is assumed that the internal quantum efficiency (the ratio of generated photons to injected carriers) in a light-emitting element containing a fluorescent compound has a theoretical limit of 25%, based on the above ratio of the singlet state to the triplet state (= 1:3).

[0005] If, on the other hand, a compound that emits phosphorescence (hereinafter referred to as a phosphorescent compound) is used, a theoretical internal quantum efficiency of 100% can be achieved. This means that a higher emission yield can be obtained than when using a fluorescent compound. For these reasons, a light-emitting element containing a phosphorescent compound has been actively developed in recent years to obtain a highly efficient light-emitting element.

[0006] As a phosphorescent compound, an organometallic complex with iridium or the like as the central metal has received particular attention due to its high phosphorescence quantum yield; an organometallic compound which has iridium as a central metal is disclosed, for example, in patent document 1 as a phosphorescent material.

[0007] When a light-emitting layer of a light-emitting element is formed using a phosphorescent compound as described above, the light-emitting layer is often formed such that the phosphorescent compound is dispersed in a matrix of another compound to suppress concentration quenching or quenching due to triplet-triplet annihilation in the phosphorescent compound. In this case, the compound serving as the matrix is ​​referred to as the host material, and the compound dispersed in the matrix, such as a phosphorescent compound, is referred to as the guest material.

[0008] There are generally several elementary methods of light emission in such a light-emitting element using a phosphorescent compound as a guest material, and descriptions of the elementary methods are given below.

[0009] (1) The case in which an electron and a hole in a guest molecule recombine and the guest molecule is excited (direct recombination process) (1-1) If the excited state of the guest molecule is an excited triplet state, the guest molecule emits phosphorescence. (1-2) If the excited state of the guest molecule is an excited singlet state, the guest molecule in the excited singlet state undergoes intersystem crossing into an excited triplet state and emits phosphorescence.

[0010] In other words, the direct recombination method in (1) can achieve a high emission efficiency as long as the efficiency of the intersystem crossing and the phosphorescence quantum yield of the guest molecule are high.

[0011] (2) The case in which an electron and a hole recombine in a host molecule and the host molecule is brought into an excited state (energy transfer process). (2-1) If the excited state of the host molecule is an excited triplet state and the triplet excitation energy level (T1 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 therefore the guest molecule is excited to a triplet state. The guest molecule in the excited triplet state emits phosphorescence. It should be noted that it is necessary to consider the reverse energy transfer from the triplet excitation energy level (T1 level) of the guest materials. Therefore, the T1 level of the host molecules must be higher than that of the guest molecules. (2-2) If the excited state of the host molecule is an excited singlet state and the S1 level of the host material is higher than the S1 level and the T1 level of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule, and therefore the guest molecule is converted into an excited singlet state or an excited triplet state. The guest molecule emits phosphorescence in the excited triplet state. Additionally, in the excited singlet state, the guest molecule undergoes intersystem crossing into an excited triplet state and emits phosphorescence.

[0012] In other words, in the energy transfer process in (2) it is important that not only the triplet excitation energy but also the singlet excitation energy of the host molecules can be transferred to the guest molecules.

[0013] With regard to the energy transfer methods described above, the emission efficiency is reduced if the host molecule itself is deactivated by emitting the excitation energy as light or heat before the excitation energy of the host molecule is transferred to the guest molecule. <Energieübertragungsverfahren>

[0014] Energy transfer processes between molecules are described in detail below. First, the following two mechanisms are proposed as mechanisms for energy transfer between molecules. A molecule that provides excitation energy is called a host molecule, while a molecule that receives the excitation energy is called a guest molecule. <<Förster-Mechanismus (Dipol-Dipol-Interaktion)> >

[0015] In the Förster mechanism (also known as Förster resonance energy transfer), no direct intermolecular contact is necessary for energy transfer. Energy transfer occurs through a resonance phenomenon of dipolar oscillation between a host molecule and a guest molecule. Through this resonance phenomenon, the host molecule provides energy to the guest molecule, thus bringing the host molecule to a ground state and the guest molecule to an excited state. The rate constant k h * →g The Förster mechanism is expressed by formula (1). [Formula 1)] kh*→g=9000c4K2ϕln10128π5n4NτR6∫f'h(ν)εg(ν)ν4dν

[0016] In formula (1) v denotes a frequency, f' h(v) denotes a normalized emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from an excited singlet state and a phosphorescence spectrum for energy transfer from an excited triplet state), ε g (v) denotes a molar absorption coefficient of a guest molecule, N denotes Avogadro's number, n denotes a refractive index of a medium, R denotes an intermolecular distance between the host molecule and the guest molecule, τ denotes a measured lifetime of an excited state (fluorescence lifetime or phosphorescence lifetime), c denotes the speed of light, ϕ denotes a luminescence quantum yield (a fluorescence quantum yield in the energy transfer from an excited singlet state and a

[0017] Phosphorescence quantum yield in energy transfer from an excited triplet state) and K 2denotes a coefficient (0 to 4) of the orientation of a transition dipole moment between the host molecule and the guest molecule. It should be noted that K 2 = 2 / 3 in statistical terms. <<Dexter-Mechanismus (Elektronenaustauschinteraktion)> >

[0018] In the Dexter mechanism (also known as Dexter electron transfer), a host molecule and a guest molecule are located near a contact-effective region where their orbitals overlap. The host molecule, which is in an excited state, and the guest molecule, which is in a ground state, exchange electrons, resulting in energy transfer. The rate constant k h*→g The Dexter mechanism is expressed by formula (2). [Formula (2)] kh*→g=(2πh)K2exp(−2RL)∫f'h(ν)εg(ν)dν

[0019] In formula (2), h denotes a Planck constant, K denotes a constant with an energy dimension, v denotes a frequency, f' h (v) denotes a normalized emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from an excited singlet state and a phosphorescence spectrum for energy transfer from an excited triplet state), ε' g (v) denotes a normalized absorption spectrum of a guest molecule, L denotes an effective molecular radius, and R denotes an intermolecular distance between the host molecule and the guest molecule.

[0020] Here, the efficiency of energy transfer from the host molecule to the guest molecule (energy transfer efficiency Φ) is to be determined. ET ) can be expressed by formula (3). In the formula, k denotes ra rate constant of a light emission process (fluorescence in the energy transfer from an excited singlet state and phosphorescence in the energy transfer from an excited triplet state) of a host molecule, k n denotes a rate constant of a non-light emission process (thermal deactivation or intersystem crossing) of a host molecule and τ denotes a measured lifetime of an excited state of a host molecule. [Formula (3)] ΦET=kh*→gkr+kn+kh*→g=kh*→g(1τ)+kh*→g

[0021] First, the energy transfer efficiency Φ can be determined according to formula (3). ET can be increased by increasing the velocity constant k h*→g The energy transfer is further increased compared to another competing rate constant kr+kn(=1 / τ). To determine the rate constant k h*→gTo increase the energy transfer based on formulas (1) and (2) in the Förster mechanism and the Dexter mechanism, it is preferred that an emission spectrum of a host molecule (a fluorescence spectrum in the case of energy transfer from an excited singlet state and a phosphorescence spectrum in the case of energy transfer from an excited triplet state) significantly overlaps with an absorption spectrum of a guest molecule (an energy difference between an excited triplet state and a ground state in the normal case of phosphorescence).

[0022] Examples of known light-emitting elements are disclosed in patent documents 2 to 4 and non-patent documents 1 and 2. References Patent document 1: WO 00 / 70 655 A2 Patent document 2: US 7,572,522 B2 Patent document 3: DE 11 2012 000 828 B4 Patent document 4: US 2008 / 0 217 608 A1 Nicht-Patentdokument 1: HINO, Yuichi; KAJII, Hirotake; OHMORI, Yutaka: Red phosphorescent organic light-emitting diodes using mixture system of small-molecule and polymer host. In: Japanese Journal of Applied Physics, Vol. 44, 2005, No. 4S, S. 2790-2794. Nicht-Patentdokument 2: KONDAKOVA, Marina E. [et al.]: High-efficiency, low-voltage phosphorescent organic light-emitting diode devices with mixed host. In: Journal of Applied Physics, Vol. 104, 2008, Nr. 9, S.094501-1 - 094501-17. Offenbarung der Erfindung

[0023] As explained above, it is possible to obtain a highly efficient light-emitting element using a phosphorescent compound. The energy transfer method teaches that a considerable overlap between the emission spectrum of a host molecule and the absorption spectrum of a guest molecule is necessary to obtain a highly efficient light-emitting element. Furthermore, the T1 level of the host molecule should be higher than that of the guest molecule to suppress the reverse energy transfer from the guest molecule to the T1 level of the host molecule.

[0024] Phosphorescent organometallic complexes (e.g., iridium complexes) used as phosphorescent guest molecules generally exhibit absorption originating from the triplet MLCT (metal ligand charge-transfer) transition in a relatively long-wavelength region. Their excitation spectra suggest that this long-wavelength absorption (mainly around 450 nm) contributes significantly to the emission of the guest molecule. Therefore, it is advantageous for this long-wavelength absorption to overlap as much as possible with the phosphorescence spectra of the host molecule. This is because such a large overlap allows for efficient energy transfer from the excited triplet state of the host molecule, leading to the efficient formation of the excited triplet state of the guest molecule.

[0025] On the other hand, the fluorescence spectrum, corresponding to the S1 level, is observed in a region of very short wavelengths, in comparison to the phosphorescence spectrum, which corresponds to the T1 level, because the S1 level of the host molecule is higher than the T1 level. This means that the overlap of the fluorescence spectrum of the host molecule with the absorption (resulting from the triplet-MLCT transition) of the guest molecule is reduced, occurring in a region of long wavelengths. Therefore, it is impossible to adequately utilize the energy transfer from the excited singlet state of the host molecule to the guest molecule.

[0026] This means that conventional light-emitting phosphorescent light-emitting elements have a very low probability that energy transfer from the excited singlet state of the host molecule to the phosphorescent guest molecule occurs in order to form the excited singlet state of the guest molecule, which is subsequently converted into the excited triplet state by intersystem crossing.

[0027] The present invention was developed with these problems in mind, and one embodiment of the present invention provides a light-emitting element based on a novel concept. Additionally, one embodiment of the present invention provides a light-emitting element with high external quantum efficiency.

[0028] One embodiment of the present invention is a light-emitting element comprising: a first electrode; a first layer above the first electrode, wherein the first layer contains a first organic compound with a hole-transporting property; a light-emitting layer above the first layer, wherein the light-emitting layer contains the first organic compound, a second organic compound with an electron-transporting property, and a compound with a light-emitting property; a second layer above the light-emitting layer, wherein the second layer contains the second organic compound;and a second electrode above the second layer, wherein the first organic compound and the second organic compound are chosen to form an exciplex, wherein a triplet excitation level of the first organic compound and a triplet excitation level of the second organic compound are higher than a triplet excitation level of the compound with a light-emitting property, wherein the compound with a light-emitting property is configured to convert energy of the triplet excitation level of the compound into light emission, and wherein a LUMO level of the compound with a light-emitting property is lower than a LUMO level of the first organic compound and the second organic compound.

[0029] Another embodiment relates to a light-emitting element comprising: a first electrode; a first electroluminescent layer above the first electrode; a charge-generating layer above the first electroluminescent layer; a second electroluminescent layer above the charge-generating layer; and a second electrode above the second electroluminescent layer, wherein at least one of the first electroluminescent layer and the second electroluminescent layer comprises: a first layer on the side of the first electrode, wherein the first layer contains a first organic compound with a hole-transporting property; a light-emitting layer above the first layer, wherein the light-emitting layer contains the first organic compound, a second organic compound with an electron-transporting property, and a compound with a light-emitting property;and a second layer above the light-emitting layer, wherein the second layer contains the second organic compound, wherein the first organic compound and the second organic compound are chosen to form an exciplex, wherein a triplet excitation level of the first organic compound and a triplet excitation level of the second organic compound are higher than a triplet excitation level of the compound with a light-emitting property, wherein the compound with a light-emitting property is configured to convert energy of the triplet excitation level of the compound into light emission, and wherein a LUMO level of the compound with a light-emitting property is lower than a LUMO level of the first organic compound and the second organic compound.

[0030] In the embodiments described above, the first organic compound exhibits an electron transport property superior to its hole transport property, and the second organic compound exhibits a hole transport property superior to its electron transport property. The first and second organic compounds are materials that form an exciplex (an excited complex). In this structure, the guest is excited by energy transfer from the exciplex to the guest, and light emission is obtained from the excited state of the guest. It should be noted that a layer other than the light-emitting layer may be capable of emitting light in response to the application of an electric current.

[0031] Exciplexes are thought to have a small energy difference between their singlet and triplet excitation energies. In other words, emission from an excited singlet state and an excited triplet state occurs in wavelength ranges that are very close to each other. Since exciplex emission is also observed in the longer wavelength range than that of their monomer states, it is possible to increase the overlap between the absorption of the phosphorescent compound, which occurs in the long-wavelength range and originates from the triplet-MLCT transition, and the emission of the exciplexes. This means that energy can be efficiently transferred from both the singlet and triplet states of the exciplexes to the phosphorescent compounds, thus improving the efficiency of the light-emitting elements.

[0032] Furthermore, exciplexes do not possess a ground state. Therefore, there is no process of reverse energy transfer from the triplet state of the guest molecule to the exciplex of the host molecule, and the reduction in the efficiency of the light-emitting element caused by this process can be neglected.

[0033] In the description, the first and second organic compounds are also referred to as n-type and p-type hosts, respectively, based on their electron transport or hole transport properties. The n-type and p-type hosts can be fluorescence-emitting materials. The ratios of the n-type and p-type hosts in the light-emitting layer are preferably 10% or more.

[0034] A region in which the proportions of the n-type and p-type hosts change continuously can be provided between the first layer and the light-emitting layer, or between the second layer and the light-emitting layer. It should be noted that the ratios of the n-type and p-type hosts can also be set to change continuously.

[0035] In the aforementioned light-emitting element, it is preferred that the phosphorescent compound be an organometallic complex. It is also preferred that the phosphorescent compound contains iridium. The phosphorescent compound can be located next to the light-emitting layer in the first layer, the second layer, a region between the light-emitting layer and the first layer, or a region between the light-emitting layer and the second layer.

[0036] In one embodiment of the present invention, the light-emitting layer contains n-type host molecules, p-type host molecules, and guest molecules. It is not necessary to point out that the molecules are not necessarily arranged regularly and may also be arranged in an almost irregular manner. In particular, if the light-emitting layer is formed as a thin film with a thickness of 50 nm or less, it is preferably amorphous, and therefore a combination on materials that hardly crystallize is preferred. Furthermore, the n-type host and the p-type host may contain two or more different types of compounds.

[0037] The light-emitting element according to one of the embodiments of the present invention can be applied to a light-emitting device, an electronic device and a lighting device.

[0038] A suitable combination of the n-type and p-type host molecules forms an exciplex when brought to an excited state. It should be noted that a necessary condition for the formation of an exciplex is that the HOMO level of the n-type host is less than the HOMO level of the p-type host, and that the LUMO level of the n-type host is less than the LUMO level of the p-type host; however, this is not a sufficient condition. For example, Alq3 and NPB satisfy the above condition but do not form an exciplex.

[0039] In contrast, if the n-type host and the p-type host form an exciplex, the guest molecules can also be excited by the process of energy transfer from the singlet and triplet states of the exciplex to the guest molecule, as mentioned above, which allows for an increase in emission efficiency compared with conventional phosphorescent light-emitting elements.

[0040] In the case where a light-emitting element has a transition between different layers, an energy gap generated at the interface causes an increase in the driving voltage and a decrease in power efficiency (see patent document 2). It is therefore preferred to reduce the number of transitions between different materials in a light-emitting element.

[0041] In each of the above embodiments, the interface between the light-emitting layer, which contains a mixture of the n-type and p-type hosts, and the n-type host layer acts as a barrier to holes but hardly as an obstacle to electrons. The interface between the light-emitting layer and the p-type host layer acts as a barrier to electrons but hardly as an obstacle to holes. Therefore, the electrons and holes are confined within or restricted to the light-emitting layer or between the n-type and p-type host layers. As a result, the electrons and holes can be prevented from reaching an anode or a cathode, respectively, thereby improving the emission efficiency. In general, exciplexes provide broad emission spectra.Since, on the other hand, the guest molecule in the embodiments of the present invention emits light, emission spectra with a small half-width can be obtained, which allow the formation of a light-emitting element capable of emitting light with excellent color purity. Brief description of the drawings Fig. Figures 1A to 1I show conceptual representations of the present invention. Fig. Figures 2A to 2D show a principle of the present invention. Fig. Figures 3A to 3E show examples of an embodiment of the present invention. Fig. Figures 4A to 4C show examples of an embodiment of the present invention. Fig. 5A and Fig. Figure 5B shows examples of an embodiment of the present invention. Fig. 6A and Fig. Figure 6B shows an example of an embodiment of the present invention. Fig. Figures 7A to 7C show the characteristics of a light-emitting element obtained in Example 1. Fig. Figures 8A to 8C show the characteristics of a light-emitting element obtained in Example 2. Best way to implement the invention

[0042] Embodiments are described with reference to the drawings. It should be noted that the invention is not limited to the following description, and it is clear to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the invention. Therefore, the invention should not be interpreted as being limited to the description in the following embodiments. It should be noted that in the structures of the invention described below, the same parts or parts with similar functions are designated by the same reference numerals in different drawings, and the description of these parts is not repeated. (Version 1)

[0043] A light-emitting element 101a, which is an example in this embodiment, comprises an n-type host layer 103 containing an n-type host, a p-type host layer 104 containing a p-type host, and a layer containing both the n-type host and the p-type host (hereinafter referred to as the light-emitting layer 102), which is arranged between these, as shown in Fig. Figure 1A shows guest molecules 105 dispersed in the light-emitting layer 102.

[0044] Fig.Figure 1B shows the distribution of the concentration of the n-type host (denoted by "N" in the diagram) and the concentration of the p-type host (denoted by "P" in the diagram) in the light-emitting element 101a. In the light-emitting layer 102 of the light-emitting element 101a, the concentration of the n-type host is 80% and the concentration of the p-type host is 20%. In other words, the ratio of the n-type host to the p-type host is 4:1. This ratio can be determined by taking into account the transport properties of the n-type and p-type hosts or the like; however, it is preferred that the concentrations of the n-type and p-type hosts in the light-emitting layer are each 10% or more.

[0045] The guest molecules 105 are dispersed in the light-emitting layer 102, as in the Fig.Figure 1C shows the present invention, but it is not limited thereto. The guest molecules 105 can be partially dispersed in the n-type host layer 103 or partially dispersed in the p-type host layer 104. It should be noted that “G” in the illustrations represents the concentration distribution of the guest molecules.

[0046] In the n-type host layer 103, the concentration of the p-type host is extremely low, at 0.1% or less, and in the p-type host layer 104, the concentration of the n-type host is also extremely low, at 0.1%. Naturally, it is not necessary for the concentrations at the interface between the light-emitting layer 102 and the n-type host layer 103, and between the light-emitting layer 102 and the p-type host layer 104, to change drastically.

[0047] Fig.Figure 1D shows an example of another light-emitting element 1b in this embodiment. The light-emitting element 101b comprises an n-type host layer 103, a p-type host layer 104, and a light-emitting layer 102, which are similar to those of the light-emitting element 101a. In addition, guest molecules 105 are dispersed in the light-emitting layer 102.

[0048] The differences to the light-emitting element 101a are that a region in which the concentration of the n-type host and the concentration of the p-type host gradually change (hereinafter referred to as the n-type transition region 106) is provided between the light-emitting layer 102 and the n-type host layer 103, and that a region in which the concentration of the n-type host and the concentration of the p-type host gradually change (hereinafter referred to as the p-type transition region 107) is provided between the light-emitting layer 102 and the p-type host layer 104.

[0049] It should be noted that the light-emitting element 101b does not necessarily have to exhibit both the n-type transition region 106 and the p-type transition region 107. In some cases, the n-type transition region 106 and the p-type transition region 107 can both have a light-emitting function. Therefore, the n-type transition region 106 and the p-type transition region 107 must be understood as a single light-emitting layer in the broadest sense. In this case, the light-emitting layer 102 can be considered a primary light-emitting layer. The n-type transition region 106 and the p-type transition region 107 can each have a thickness of 1 nm to 50 nm.

[0050] Fig.Figure 1E shows the distribution of the concentrations of the n-type and p-type hosts, and the concentrations of the n-type and p-type hosts change continuously in the transition region 106 (n-type) and the transition region 107 (p-type). Additionally, as shown in Fig. As shown in Figure 1F, guest molecules 105 are provided not only to be contained in the light-emitting layer 102, but also in the n-type transition region 106 and the p-type transition region 107, and can furthermore be provided to be partially contained in the n-type host layer 103 and the p-type host layer 104. It is not necessary to state that the guest molecules can also be provided only in the light-emitting layer 102.

[0051] Fig.Figure 1C shows an example of another light-emitting element 1c in this embodiment. In the light-emitting element 101c, the concentration of the n-type host and the concentration of the p-type host change continuously in a range that lies between the n-type host layer 103 and the p-type host layer 104, as shown in the Fig. 1H is shown. In this case, it is difficult to define a light-emitting layer (or main light-emitting layer), as with light-emitting element 101a and light-emitting element 101b; however, a region in which the n-type and p-type hosts are mixed and the concentrations of the n-type and p-type hosts are each 10% or more can be considered a light-emitting layer in the broadest sense.

[0052] The guest's concentration can be adjusted so that the guest is contained, in the broadest sense, within the light-emitting layer, as in Fig. 1I is shown. It should be noted that in each of the Fig. 1A to 1I, the host layer 104 of p-type is provided on the host layer 103 of n-type, with the light-emitting layer 102 located between them. However, this structure is provided for simplification, and it will be recognized that the reverse structure is also included in the embodiment of the present invention in which the host layer 103 of n-type is provided on the host layer 104 of p-type.

[0053] The energy levels of the above light-emitting element 101a are determined with reference to the Fig.2A described. As stated above, the HOMO levels and the LUMO levels of the n-type and p-type hosts have the following relationship: HOMO level of the n-type host < HOMO level of the p-type host < LUMO level of the n-type host < LUMO level of the p-type host.

[0054] On the other hand, in the light-emitting layer 102, where the n-type and p-type hosts are mixed, it can be observed that, from the point of view of carrier transfer, the HOMO level corresponds to the HOMO level of the p-type host and the LUMO level corresponds to the LUMO level of the n-type host, since holes and electrons are transferred using the HOMO and LUMO levels of the p-type host, respectively. As a result, there is a gap between the LUMO levels at the interface between the light-emitting layer 102 and the p-type host layer 104, which acts as a barrier to electron transfer. Similarly, at the interface between the light-emitting layer 102 and the n-type host layer 103, there is a gap between the HOMO levels, which serves as a barrier for hole transfer.

[0055] On the other hand, at the interface between the p-type light-emitting layer 102 and the p-type host layer 104, the HOMO levels are the same, and therefore there is no barrier to hole transfer, and at the interface between the n-type light-emitting layer 102 and the n-type host layer 103, the HOMO levels are the same, and therefore there is no barrier to electron transfer.

[0056] As a result, electrons are simply transferred from the n-type host layer 103 to the light-emitting layer 102. However, the gap between the LUMO levels of the light-emitting layer 102 and the p-type host layer 104 prevents electron transfer from the light-emitting layer 102 to the p-type host layer 104.

[0057] Similarly, holes are readily transferred from the p-type host layer 104 to the light-emitting layer 102, but the gap between the HOMO levels of the light-emitting layer 102 and the n-type host layer 103 prevents the transfer of holes from the light-emitting layer 102 to the n-type host layer 103. As a result, electrons and holes can become trapped in the light-emitting layer 102.

[0058] The energy levels of the above light-emitting element 101b are determined with reference to Fig. 2B described. Although the HOMO levels and the LUMO levels of the light-emitting layer 102, the n-type host layer 103 and the p-type host layer 104 are the same as those in Fig. In 2A, transition zone 106 (n-type) and transition zone 107 (p-type) should be noted. In these zones, the concentration of the n-type and p-type hosts changes continuously.

[0059] Unlike the case where the conduction band and valence band of an inorganic semiconductor material (e.g., Ga) x In 1-x N (0 <x<1)) kontinuierlich mit einer Änderung der Zusammensetzung verändern, verändern sich das LUMO-Niveau und das HOMO-Niveau einer gemischten organischen Verbindung kaum. Dies liegt daran, dass die elektrische Leitung einer organischen Verbindung eine Hopping-Leitung ist, welche sich von der elektrischen Leitung eines anorganischen Halbleiters unterscheidet.

[0060] For example, if the concentration of the n-type host decreases and the concentration of the p-type host increases, electrons are less likely to be transferred. This is not because the LUMO level continuously increases, but because the probability of transfer decreases due to an increase in the distance between the n-type host molecules and because additional energy is needed to hop to a LUMO level of a neighboring p-type host that has a higher LUMO level than the n-type host.

[0061] Therefore, in the transition region 106 of the n-type, the HOMO is in a mixed state of the HOMOs of the host of the n-type and the host of the p-type, and in particular, the HOMO tends to correspond more to the HOMO of the host of the p-type in a region near the light-emitting layer 102 and tends to correspond more to the HOMO of the host of the n-type in a region near the host layer 103 of the n-type.

[0062] Even in the presence of the p-type transition region 106 and the p-type transition region 107, as described above, there is a gap between the LUMO levels at the interface between the p-type light-emitting layer 102 and the p-type host layer 104, which acts as a barrier to electron transfer, and at the interface between the n-type light-emitting layer 102 and the n-type host layer 103, there is a gap between the HOMO levels, which acts as a barrier to hole transfer. This corresponds to the Fig. 2A.

[0063] It should be noted that an interface with a drastic change in concentration, as in Fig. 2A, leads to a problem of the high probability of interface destruction, since electrons, for example, tend to concentrate at the interface. In contrast, an indistinct interface, as in Fig.2B, does not lead to the destruction of a specific region, as the electrons remain in probabilistically determined regions. In other words, it is possible to suppress the destruction of the light-emitting element, thereby increasing its reliability.

[0064] On the other hand, at the interface between the light-emitting layer 102 and the p-type transition region 107 and at the interface between the p-type transition region 107 and the p-type host layer 104, the HOMO levels are the same, and therefore there is no barrier to hole transfer. At the interface between the light-emitting layer 102 and the n-type transition region 106 and at the interface between the n-type transition region 106 and the n-type host layer 103, the LUMO levels are the same, and therefore there is no barrier to electron transfer.

[0065] As a result, electrons are easily transferred from the n-type host layer 103 to the light-emitting layer 102; however, the gap between the LUMO levels of the p-type transition region 107 prevents electron transfer from the light-emitting layer 102 to the p-type host layer 104. Similarly, holes are easily transferred from the p-type host layer 104 to the light-emitting layer 102; however, the gap between the HOMO levels of the n-type transition region 106 prevents hole transfer from the light-emitting layer 102 to the n-type host layer 103.

[0066] As a result, holes and electrons can be trapped in the light-emitting layer 102. Similarly, in the case of the light-emitting element 101c, where the concentration of the n-type and p-type hosts changes continuously between the n-type host layer 103 and the p-type host layer 104, it can be assumed that electrons and holes are effectively trapped between the n-type host layer 103 and the p-type host layer 104.

[0067] The excitation methods and processes of the guest molecules 105 are described below. Light-emitting element 101a is used as an example in this description; the same applies to light-emitting elements 101b and 101c. As described above, the excitation methods include direct recombination and energy transfer.

[0068] Fig.Figure 2C shows the direct recombination process in which electrons are injected into the LUMO of the light-emitting layer 102 from the n-type host layer 103, which is connected to the cathode, and holes are injected into the HOMO of the light-emitting layer 102 from the p-type host layer 104, which is connected to the anode. Since guest molecules 105 are present in the light-emitting layer 102, the guest molecules can be excited (transformed into an intramolecular exciton) by injecting electrons and holes into the LUMO and HOMO of the guest molecules under suitable conditions.

[0069] However, it is technically difficult to efficiently inject electrons and holes into the LUMO and HOMO of the guest molecules, which are thinly distributed in the light-emitting layer 102; therefore, the probability of the procedure is not high enough. The efficiency can be increased by adjusting the guest's LUMO to be 0.1 eV to 0.3 eV lower than the LUMO of the n-type host, so that the guest molecules preferentially capture electrons. A similar effect can be achieved by adjusting the guest's HOMO to be 0.1 eV to 0.3 eV higher than the HOMO of the p-type host. It should be noted that the guest's HOMO is lower than that of the p-type host in Fig. 2C. However, the electron is efficiently captured because the LUMO of the guest is sufficiently lower than that of the n-type and p-type hosts.

[0070] It is not preferred to set the LUMO of the guest to be 0.5 eV or more lower than the LUMO of the n-type host (or to set the HOMO of the guest to be 0.5 eV or more higher than the HOMO of the p-type host), because although the probability of trapping electrons (holes) increases, the conductivity of the light-emitting layer 102 decreases and only the guest molecules on the cathode side (anode side) are locally excited.

[0071] Fig.Figure 2D shows the formation of the exciplex by a suitable selection of the n-type and p-type host molecules according to the present invention. In cases where electrons and holes are injected into the light-emitting layer 102 in the manner described above, the probability of the electrons and holes colliding in the n-type and p-type host molecules in the light-emitting layer is high, compared to the probability of them colliding in the guest molecules. In such a case, an exciplex is formed. Here, an exciplex is described in detail.

[0072] The exciplex is formed by an interaction between dissimilar molecules in excited states. The exciplex is generally known to be formed simply between an organic compound with a relatively low LUMO level (an n-type host) and an organic compound with a relatively low HOMO level (a p-type host).

[0073] The emission wavelength of the exciplex depends on the energy difference between the HOMO and LUMO levels of the n-type and p-type hosts, respectively. A large energy difference results in a short emission wavelength. When the exciplex is formed by molecules from both the n-type and p-type hosts, the LUMO and HOMO levels of the exciplex originate from the n-type and p-type hosts, respectively.

[0074] Therefore, the energy difference of the exciplex is smaller than the energy difference of the n-type host and the energy difference of the p-type host. In other words, the emission wavelength of the exciplex is longer than the emission wavelength of the n-type host and the p-type host.

[0075] The manufacturing process of Exciplex can be roughly divided into two processes. < <elektroplex>>

[0076] In this description, the term "electroplex" means an exciplex formed directly by the n-type host in its ground state and the p-type host in its ground state. For example, an electroplex is an exciplex formed directly by an anion of the n-type host and a cation of the p-type host.

[0077] As described above, in the energy transfer process of the light emission process of a conventional organic compound, an electron and a hole in a host molecule are recombined (leading to excitation) and the excitation energy is transferred from the host material in the excited state to a guest molecule, thereby bringing the guest molecule into an excited state to emit light.

[0078] At this point, before the excitation energy is transferred from the host molecule to the guest molecule, the host molecule may itself emit light, or the excitation energy may be converted into thermal energy, leading to deactivation of the excitation energy. In particular, if the host molecule is in an excited singlet state, the excitation lifetime is shorter than if it is in an excited triplet state, which readily leads to deactivation of the singlet excitation energy. Deactivation of the excitation energy is one of the reasons for a reduction in the lifetime of the light-emitting element.

[0079] However, if an electroplex is formed between the n-type and p-type host molecules, both of which possess carriers (cation or anion), the formation of a singlet exciton with a short excitation lifetime can be suppressed. In other words, there is a process in which an electroplex is formed directly without the formation of a singlet exciton. Therefore, the deactivation of the singlet excitation energy of either the n-type or p-type host molecule can be prevented. Consequently, a long-life light-emitting element can be obtained.

[0080] It is a novel concept to obtain a light-emitting element with high emission efficiency by suppressing the generation of the excited singlet state of a host molecule and transferring the energy from an electroplex formed in its place to a guest molecule in the manner described above. <<Bildung eines Exciplex durch ein Exziton> >

[0081] Another method involves a basic process in which one of the host molecules, either n-type or p-type, generates a singlet exciton and then interacts with the other in its ground state to form an exciplex. Unlike an electroplex, an excited singlet state of either the n-type or p-type host molecule is only temporarily generated in this case, but is quickly converted into an exciplex. Therefore, the deactivation of the singlet excitation energy can be prevented. Thus, it is possible to prevent the deactivation of the host molecule's excitation energy.

[0082] It should be noted that if the difference between the HOMO levels of the n-type and p-type hosts and the difference between the LUMO levels of the n-type and p-type hosts is large (especially 0.3 eV or more), electrons are preferably injected into the n-type host molecule and holes are preferably injected into the p-type host molecule. In this case, the process by which an electroplex is formed is considered to have priority over the process by which an exciplex is formed by a singlet exciton.

[0083] It should be noted that, to increase the efficiency of the energy transfer process, it is preferable that, in the Förster mechanism or the Dexter mechanism described above, the overlap between the emission spectrum of an electroplex and / or an exciplex and the absorption spectrum of a guest is greater than the overlap between the emission spectrum of an n-type (p-type) host alone (or the corresponding energy difference) and the absorption spectrum of the guest, taking into account the importance of the absorption of the MLCT transition.

[0084] To further increase the energy transfer efficiency, it is preferred to increase the concentration of the guest to such an extent that no concentration quenching occurs, and it is preferred that the concentration of the guest relative to the total number of n-type and p-type hosts is 1 wt.% to 9 wt.%.

[0085] It should be noted that, regardless of whether the excitation method is the direct recombination method or the energy transfer method, no concept is yet known in which guest molecules in the n-type and p-type hosts are excited by energy transfer from the exciplex and / or electroplex of the n-type and p-type hosts to the guest molecules. In the description, this concept is referred to as "Guest Coupled with Complementary Hosts" (GCCH). This concept not only enables the simultaneous confinement of the carriers and the reduction of the carrier injection barrier into the light-emitting layer, but also allows the use of the energy transfer method from both the excited singlet and triplet states, leading to the formation of a highly efficient light-emitting element (i.e., the power efficiency is exceptionally high) at low driving voltage. (Version 2)

[0086] Fig. 3A shows an example of a light-emitting device. The in Fig. The light-emitting device shown in Figure 3A comprises a light-emitting element 101, as described in embodiment 1 (such as light-emitting element 101a, light-emitting element 101b, or light-emitting element 101c, as described in embodiment 1), arranged between a cathode 108 and an anode 109. It should be noted that the cathode 108 and the anode 109 are preferably transparent. This light-emitting device can preferably be provided on a suitable substrate.

[0087] In the light-emitting element 101, the n-type host layer 103 and the p-type host layer 104, between which the light-emitting layer 102 is arranged, serve as its electron transport layer and hole transport layer, respectively, and serve to block holes and electrons, as described above. Therefore, layers corresponding to an electron transport layer and a hole transport layer do not need to be provided additionally. Consequently, the in Fig. The method shown in Figure 3A for manufacturing a light-emitting device can be simplified.

[0088] The light-emitting element 101 comprises a guest, an n-type host, and a p-type host, as described in embodiment 1. Two or more types of substances can be used as the n-type host (or n-type host).

[0089] An organometallic complex is preferred as the guest, and an iridium complex is particularly preferred. Considering the energy transfer due to the Förster mechanism described above, the molar absorption coefficient of the absorption band of the phosphorescent compound located on the side of the longest wavelength is preferably 2000 M. -1 ·cm -1 or more, preferably 5000 m -1 ·cm -1 or more.

[0090] Examples of compounds with such a high molar absorption coefficient are bis(3,5-dimethyl-2-phenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)], see the first chemical formula below), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)], see the second chemical formula below), and the like. In particular, if a material has a molar absorption coefficient of 5000 M -1 ·cm -1 or more, such as [Ir(dppm)2(acac)], a light-emitting element can be obtained, as an external quantum efficiency of 30% can be achieved.

[0091] The n-type host is represented by a compound with a heteroaromatic ring exhibiting π-electron deficiency. That is, a compound with a 6-membered aromatic ring, which includes a heteroatom (nitrogen, phosphorus) with a higher electronegativity than carbon as a constituent element of the ring. For example, the n-type host can be one of the compounds that has a benzoquinoxaline skeleton (benzoquinoxaline derivative) that readily accepts electrons, such as 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[4-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2DBTPDBq-II), 2-[4-(3,6-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) and 6-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II).

[0092] The p-type host is represented by an aromatic amine (a compound in which at least one aromatic ring is bonded to a nitrogen atom) or a carbazole derivative. For example, the p-type host can be any compound that readily accepts holes, such as 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), and 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP). It should be noted that the present invention is not limited to these compounds, as long as the combination of the n-type and p-type hosts forms an exciplex.

[0093] The anode 109 is preferably formed using metals, alloys, conductive compounds, mixtures thereof, and the like, which exhibit a high work function (particularly 4.0 eV or more). Specific examples include indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxide containing tungsten oxide and zinc oxide (IWZO), and the like. Films of these conductive metal oxides are generally formed by a sputtering process, but can also be formed by applying a sol-gel process or the like.

[0094] For example, an indium oxide-tin oxide film can be formed by a sputtering process using a target in which zinc oxide is added to indium oxide at a rate of 1 wt% to 20 wt%. Furthermore, an IWZO film can be formed by a sputtering process using a target in which tungsten oxide is added to indium oxide at a rate of 0.5 wt% to 5 wt%, and zinc oxide is added to indium oxide at a rate of 0.1 wt% to 1 wt%. Other examples include graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, nitrides of metallic materials (e.g., titanium nitride), and the like.

[0095] It should be noted that if a layer contained in the light-emitting element 101, formed in contact with the anode, is formed using a composite material described below, which is formed by combining an organic compound and an electron acceptor, any of a variety of metals, alloys, electrically conductive compounds, mixtures thereof, and the like can be used as the anode substance, regardless of the work function; e.g., aluminum, silver, an aluminum-containing alloy (e.g., Al-Si), or the like can also be used. The anode can be formed, for example, by a sputtering process or an evaporation process (including a vacuum evaporation process).

[0096] The cathode 108 is preferably formed using metals, alloys, electrically conductive compounds, mixtures thereof, and the like, which have a low work function (preferably 3.8 eV or less). Specific examples of these include elements belonging to groups 1 and 2 of the periodic table, i.e., alkali metals such as lithium and cesium, alkaline earth metals such as calcium and strontium, magnesium, their alloys (e.g., Mg-Ag and Al-Li), rare earth metals such as europium and ytterbium, their alloys, aluminum, silver, and the like.

[0097] When a layer contained in the light-emitting element 101 and formed in contact with the cathode 108 is created using a composite material described later, formed by combining an organic compound and an electron donor (a donor), a variety of conductive materials, such as Al, Ag, ITO, and indium oxide-tin oxide containing silicon or silicon oxide, can be used, regardless of the work function. It should be noted that, for the formation of the cathode, a vacuum evaporation process or a sputtering process can be used. In the case of the use of a silver paste or the like, a coating process, an inkjet process, or the like can be employed.

[0098] Fig. 3B shows an example of a light-emitting device. The in Fig. The light-emitting device shown in Figure 3B is one in which an electron injection layer 113 is provided between the light-emitting element 101 and the cathode 108, and a hole injection layer 114 is provided between the light-emitting element 101 and the anode 109 in the Fig. The light-emitting device shown in 3A is provided.

[0099] When the electron injection layer 113 and the hole injection layer 114 are provided, electrons and holes can be efficiently injected into the light-emitting element from the cathode 108 and the anode 109, thereby increasing energy efficiency. A stack of the light-emitting element 101, the electron injection layer 113, and the hole injection layer 114 is referred to as an EL layer 110.

[0100] The injection layer 114 is a layer containing a substance with high injection properties. This substance can be a metal oxide 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, a phthalocyanine-based compound such as phthalocyanine (abbreviation: H₂Pc) or copper(II) phthalocyanine (abbreviation: CuPc) can be used.

[0101] Other examples of the substance that can be used are aromatic amine compounds and the like, which are low-molecular-weight 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), 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B), 3-[N-(9-Phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2) and 3-[N-(1-Naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1).

[0102] Other examples of the substance that can be used are polymers (e.g., oligomers, dendrimers, and polymers) such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: poly-TPD), and high-molecular-weight compounds to which acid is added, such as poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PE-DOT / PSS) and polyaniline / poly(styrenesulfonic acid) (PAni / PSS).

[0103] For the hole injection layer 114, the composite material formed by combining an organic compound and an electron acceptor can be used. Such a composite material, in which holes are formed in the organic compound by the electron acceptor, exhibits high hole injection and hole transport properties. In this case, the organic compound is preferably a material that is excellent at conducting generated holes (a substance with high hole transport properties).

[0104] Examples of the organic compound used for the composite material can be a variety of compounds, such as aromatic amines, carbazole derivatives, aromatic hydrocarbons, and polymers (e.g., oligomers, dendrimers, and polymers). The organic compound used for the composite material is preferably an organic compound with high hole transport properties and is particularly preferably a substance with a hole mobility of 10 -6 cm 2 / Vs or more. It should be noted that, in addition to these substances, any substance that has the property of transporting more holes than electrons can be used. Organic compounds that can be used are described in detail below.

[0105] Examples of organic compounds that can be used as the aromatic material are 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) and 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), and carbazole derivatives such as 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(N-carbazolyl)phenyl]-10-phenylanthracene (abbreviation: CzPA), 9-Phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PczPA) and 1,4-Bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

[0106] Other examples of the organic compound that can be used are aromatic hydrocarbon compounds such as 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnth), and 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 and 2,3,6,7-Tetramethyl-9,10-di(1-naphthyl)anthracene.

[0107] Other examples of organic compounds that can be used are aromatic hydrocarbons, such as 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthryl, 10,10'-diphenyl-9,9'-bianthryl, 10,10'-bis(2-phenylphenyl)-9,9'-bianthryl, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthryl, anthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, pentacene, coronene, 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi) and 9,10-Bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA).

[0108] Furthermore, examples of electron acceptors include organic compounds such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ) and chloranil, oxides of transition metals, oxides of metals belonging to groups 4 to 8 of the periodic table, and the like. Vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are particularly preferred due to their high electron-accepting properties. Among these, molybdenum oxide is especially preferred because it is stable in air, has low hygroscopic properties, and is easy to handle.

[0109] The composite material can be formed using the electron acceptor and polymer described above, such as PVK, PVTPA, PTPDMA or Poly-TPD, and can be used for the hole injection layer 114.

[0110] The electron injection layer 113 is a layer containing a substance with high electron injection properties. Examples of substances that can be used for the electron injection layer 113 are alkali metals, alkaline earth metals and their compounds, such as lithium, cesium, calcium, lithium fluoride, cesium fluoride, calcium fluoride and lithium oxide, and rare earth metal compounds, such as erbium fluoride.

[0111] For the electron injection layer 113, a substance with high electron transport properties can also be used. Examples of substances with high electron transport properties are metal complexes such as Alq3, Tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3), Bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq2), Balq, Zn(BOX)2 and Bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)2).

[0112] Other examples of these are heteroaromatic compounds, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), and 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (Abbreviation: BzOs).

[0113] Other examples are polymers such as poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), and poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy). The substances mentioned here are mainly substances with an electron mobility of 10 -6 cm 2 / Vs or more.

[0114] It should be noted that, in addition to these substances, any substance that has the property of conducting more electrons than holes can be used for the electron injection layer 113. These substances with high electron transport properties can be used for the electron transport layer described below.

[0115] Alternatively, a composite material formed by combining an organic compound and an electron donor (donor) can be used for the electron injection layer 113. Such a composite material, in which electrons are generated in the organic compound by the electron donor, exhibits high electron injection and electron transport properties. The organic compound is preferably a material that is excellent at conducting generated electrons, and in particular, any of the above substances (such as metal complexes and heteroaromatic compounds) can be used for the electron transport layer.

[0116] A substance that exhibits electron-donating properties with respect to the organic compound can be used as the electron donor. Preferred examples of electron donors are alkali metals, alkaline earth metals, and rare earth metals, such as lithium, cesium, magnesium, calcium, erbium, and ytterbium. Any alkali metal oxide and alkaline earth oxide is preferred, such as lithium oxide, calcium oxide, barium oxide, and the like. A Lewis base, such as magnesium oxide, or an organic compound, such as tetrathiafulvalene (abbreviation: TTF), can also be used.

[0117] Fig. 3C shows an example of a light-emitting device. The light-emitting device, which is in Fig. Figure 3C shows a structure in which an electron transport layer 111 is provided between the light-emitting element 101 and the electron injection layer 113, and a hole transport layer 112 is provided between the light-emitting element 101 and the hole injection layer 114 in the light-emitting device, which is in Fig. 3B is shown, provided.

[0118] As described above, the n-type host layer 103 and the p-type host layer 104 also serve as an electron transport layer and a hole transport layer, respectively. To inject electrons and holes into the light-emitting element 101 more efficiently, it is preferred that the electron transport layer 111 and the hole transport layer 112 are additionally provided.

[0119] The electron transport layer 111 is a layer containing a substance with high electron transport properties. The substance with high electron transport properties described above can be used for the electron transport layer 111. The electron transport layer is not limited to a single layer and can be a stack of two or more layers containing one of the substances mentioned above.

[0120] The hole transport layer 112 is a layer containing a substance with high hole transport properties. Examples of substances with high hole transport properties are aromatic amine compounds such as NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), and 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB). The substances mentioned here are mainly substances that have a hole mobility of 10 -6 cm 2 exhibiting / Vs or more. It should be noted that the layer containing a substance with high hole transport properties is not limited to a single layer and can be a stack of two or more layers, which may contain any of the above substances.

[0121] For the hole transport layer 112, a carbazole derivative, such as CBP, CzPA, or PczPA, or an anthracene derivative, such as t-BuDNA, DNA, or DPAnth, can be used. A high-molecular-weight compound, such as PVK, PVTPA, PTPDMA, or poly-TPD, can also be used for the hole transport layer 112.

[0122] It should be noted that the hole injection layer 114, the hole transport layer 112, the light-emitting element 101, the electron transport layer 111, and the electron injection layer 113, as mentioned above, can each be formed by a process such as an evaporation process (including a vacuum evaporation process), an inkjet process, or a coating process. It should be noted that the EL layer 110 does not necessarily have to contain all of these layers.

[0123] As in Fig. In a 3D representation, a multitude of EL layers 110a and 110b can be stacked between the anode 109 and the cathode 108. In this case, the EL layers 110a and 110b each contain at least one light-emitting element, as shown in Fig. 3A shown, or the EL layer 110, which is in the Fig. 3A and Fig. Figure 3B shows a charge generation layer 115 located between the stacked EL layers 110a and 110b. The charge generation layer 115 can be formed using a substance with high hole injection properties or the composite material described above.

[0124] In this case, the layer containing another material can be a layer containing an electron donor substance and a substance with high electron transport properties, a layer formed from a transparent conductive film, or the like. Furthermore, a light-emitting element can have a structure in which phosphorescence is obtained from one of the EL layers and fluorescence from the other. Phosphorescence can be achieved by using the EL layer structures described above.

[0125] Furthermore, by making the emission colors of the EL layers different, light of a desired color can be obtained from the light-emitting element as a whole. For example, the emission colors of EL layers 110a and 110b are complementary, so that the light-emitting device as a whole can emit white light. The same applies to a light-emitting element with three or more EL layers.

[0126] Alternatively, as in Fig. Figure 3E shows an EL layer 110 containing the hole injection layer 114, the hole transport layer 112, the light-emitting element 101, the electron transport layer 111, an electron injection buffer layer 116, an electron relay layer 117, and a composite material layer 118, which is in contact with the second electrode 108, between the anode 109 and the cathode 108.

[0127] It is preferred to provide the composite material layer 118, which is in contact with the cathode 108, since in this case damage to the EL layer 110, especially if the cathode 108 is formed by a sputtering process, can be reduced. The composite material layer 118 can be formed using the composite material described above, in which an organic compound with high hole transport properties contains an acceptor substance.

[0128] Furthermore, by providing the electron injection buffer layer 116, an injection barrier between the composite material layer 118 and the electron transport layer 111 can be reduced, therefore electrons generated in the composite material layer 118 can be easily injected into the electron transport layer 111.

[0129] The electron injection buffer layer 116 can be a substance with a high electron injection property, such as an alkali metal, an alkaline earth metal, a rare earth metal, a compound of the above metal (e.g. an alkali metal compound (including an oxide, such as lithium oxide, a halide and a carbonate, such as lithium carbonate or cesium carbonate), an alkaline earth metal compound (including an oxide, a halide and a carbonate) or a rare earth metal compound (including an oxide, a halide and a carbonate).

[0130] Furthermore, in a case where the electron injection buffer layer 116 contains a substance with high electron transport properties and a donor substance, the donor substance is preferably added such that the mass ratio of the donor substance to the substance with high electron transport properties is in the range of 0.001:1 to 0.1:1. A material similar to the electron transport material described above can be used as the substance with high electron injection properties.

[0131] The donor substance can be an organic compound such as tetrathianaphthacene (abbreviation: TTN), nickelocene or decamethylnickelocene, as well as an alkali metal, alkaline earth metal, rare earth metal, a compound of the above metal (e.g. an alkali metal compound (including an oxide, such as lithium oxide, a halide and a carbonate, such as lithium carbonate or cesium carbonate), an alkaline earth metal compound (including an oxide, such as lithium oxide, a halide and a carbonate) and an alkaline earth metal (including an oxide, such as lithium oxide, a halide and a carbonate).

[0132] Furthermore, it is preferred that the electron relay layer 117 is formed between the electron injection buffer layer 116 and the composite material layer 118. The electron relay layer 117 is not necessarily provided; by providing the electron relay layer 117 with high electron transport properties, electrons can be quickly directed into the electron injection buffer layer 116.

[0133] The structure in which the electron relay layer 117 is arranged between the composite material layer 118 and the electron injection buffer layer 116 is a structure in which the acceptor substance contained in the composite material layer 118 and the donor substance contained in the electron injection buffer layer 116 are less likely to interact with each other, and therefore their functions hardly impair each other. Therefore, an increase in the drive voltage can be prevented.

[0134] The electron relay layer 117 contains a substance with a high electron transport property and is designed such that the LUMO level of the substance with high electron transport property is located between the LUMO level of the acceptor substance contained in the composite material layer 118 and the LUMO level of the substance with high electron transport property contained in the electron transport layer 111.

[0135] In the case that the electron relay layer 117 contains a donor substance, the donor energy level of the donor substance is controlled such that it lies between the LUMO level of the acceptor substance contained in the composite material layer 118 and the LUMO level of the substance with high electron transport properties contained in the electron transport layer 111. As a specific energy level value, the LUMO level of the substance with high electron transport properties contained in the electron relay layer 117 is preferably -5.0 eV or more, more preferably -5.0 eV or more and -3.0 eV or less.

[0136] The substance with high electron transport properties contained in the electron relay layer 117 may preferably be a phthalocyanine-based material or a metal complex with a metal-oxygen bond and an aromatic ligand.

[0137] The phthalocyanine-based material contained in the electron relay layer 707 preferably includes any of CuPc, a phthalocyanine tin(II) complex (SnPc), a phthalocyanine zinc complex (ZnPc), cobalt(II) phthalocyanine β-form (CoPc), phthalocyanine iron (FePc) and vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (PhO-VOPc).

[0138] The metal complex with a metal-oxygen bond and an aromatic ligand contained in the electron relay layer 117 is preferably a metal complex with a metal-oxygen double bond. The metal-oxygen double bond exhibits acceptor properties (the ability to readily accept electrons); therefore, electrons can be conducted (given and received) more easily. Furthermore, the metal complex with a metal-oxygen double bond is considered stable. Therefore, the use of the metal complex with the metal-oxygen double bond allows for an improvement in the lifetime of the light-emitting device.

[0139] As the metal complex with a metal-oxygen bond and an aromatic ligand, a phthalocyanine-based material is preferred. In particular, any of vanadyl phthalocyanine (VOPc), a phthalocyanine tin(IV) oxide complex (SnOPc), a phthalocyanine titanium dioxide complex (TiOPc), and the like are preferred due to their high acceptor properties.

[0140] It should be noted that, of the phthalocyanine-based materials mentioned above, a phthalocyanine-based material with a phenoxy group is preferred. In particular, a phthalocyanine derivative with a phenoxy group, such as PhO-VOPc, is preferred. The phthalocyanine derivative with a phenoxy group is soluble in a solvent and therefore has the advantage of being easy to handle during the formation of a light-emitting element and of simplifying the maintenance of an apparatus used for film production.

[0141] The electron relay layer 117 can furthermore contain a donor substance. The donor substance can be an organic compound such as tetrathianaphthacene (abbreviation: TTN), nickelocene, or decamethylnickelocene, as well as an alkali metal, an alkaline earth metal, a rare earth metal, or a compound of the above metal (e.g., an alkali metal compound (including an oxide, such as lithium oxide, a halide, and a carbonate, such as lithium carbonate or cesium carbonate), an alkaline earth metal compound (including an oxide, a halide, and a carbonate), and a rare earth metal compound (including an oxide, a halide, and a carbonate)). If such a donor substance is contained in the electron relay layer 117, electrons can be easily conducted, and the light-emitting element can be operated at low voltage.

[0142] In the case where a donor substance is contained in the electron relay layer 117, in addition to the materials mentioned above as having high electron transport properties, a substance with a higher LUMO level than the acceptor substance contained in the composite material layer 118 can be used. In particular, it is preferred to use a substance with a LUMO level of -5.0 eV or more, preferably -5.0 eV or more and -3.0 eV or less. Examples of such a substance include a perylene derivative, a nitrogen-containing condensed aromatic compound, and the like. It should be noted that a nitrogen-containing condensed compound is preferably used for the electron relay layer 117 due to its stability.

[0143] Specific examples of the perylene derivative are 3,4,9,10-perylenetetracarboxyl dianhydride (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxyl-bis-benzimidazole (abbreviation: PTCBI), N,N'-dioctyl-3,4,9,10-perylenetetracarboxyldiimide (abbreviation: PTCDI-C8H), N,N'-dihexyl-3,4,9,10-perylenetetracarboxyldiimide (abbreviation: Hex PTC) and the like.

[0144] Specific examples of nitrogen-containing condensed aromatic compounds are pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation: PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT(CN)6), 2,3-diphenylpyrido[2,3-b]pyrazine (abbreviation: 2PYPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (abbreviation: F2PYPR) and the like.

[0145] Furthermore, 7,7,8,8-tetracyanoquinodimethane (abbreviation: TCNQ), 1,4,5,8-naphthalenetetracarboxylic acid dianhydride (abbreviation: NTCDA), perfluoropentacene, copper hexadecafluorophthalocyanine (abbreviation: F) 16 CuPc), N,N'-Bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (abbreviation: NTCDI-C8F), 3',4'-Dibutyl-5,5''-bis(dicyanomethylene)-5,5''-dihydro-2,2':5',2''-terthiophene (abbreviation: DCMT), Methanofullerenes (e.g. [6,6]-Phenyl C 61 butyric acid methyl ester) or the like.

[0146] It should be noted that in the case where a donor substance is contained in the electron relay layer 117, the electron relay layer 117 can be formed by a process such as co-evaporation of the substance with a high electron transport property and the donor substance.

[0147] It should be noted that, as described above, the n-type host layer 103 and the p-type host layer 104 in the light-emitting element 101 also serve as an electron transport layer and a hole transport layer, respectively; therefore, the electron transport layer 111 or the hole transport layer does not necessarily need to be provided. In this case, the n-type host layer 103 serves as the electron transport layer 111.

[0148] In the light-emitting device described above, a current flows due to a potential difference between the anode and the cathode, and holes and electrons recombine in the EL layer 110 (or 110a or 110b), thus emitting light. This light emission is then transmitted to the outside either through the anode or the cathode, or both. Therefore, either the anode or the cathode, or both, is an electrode with the property of transmitting or transmitting visible light.

[0149] It should be noted that a hole-blocking layer can be combined with the light-emitting element 101.

[0150] Using the light-emitting element described in this embodiment, a light-emitting device with a passive matrix or a light-emitting device with an active matrix can be produced, in which the control of the light-emitting element is achieved by means of a transistor. According to the present invention, the light-emitting element can be used in an electronic device or a lighting device. (Version 3)

[0151] In this embodiment, devices and methods for manufacturing the light-emitting element 101a or the like, which was described in embodiment 1, are described. A manufacturing device or apparatus, which in Fig. As shown in Figure 4A, the system comprises a first evaporation source 202, a second evaporation source 203, and a third evaporation source 204 in a vacuum chamber 201. The first to third evaporation sources 202 to 204 each have a linear opening region 223, as shown in the Fig. 4C is represented, and allows its internal organic compound to evaporate through a resistance heating process.

[0152] In this arrangement, the first evaporation source 202, the second evaporation source 203, and the third evaporation source 204 cause the n-type host and the p-type host, respectively, to evaporate. The first to third evaporation sources 202 to 204 can each be equipped with an orifice plate. Furthermore, it is preferred that the temperatures of the evaporation sources can be controlled independently, so that the vapor pressures of the organic compounds can be controlled as desired. For example, the evaporation rate of the n-type host can be set to be four times that of the p-type host, and the evaporation rate of the guest can be set to 1% of the evaporation rate of the p-type host.

[0153] Furthermore, the opening regions 223 of the evaporation sources can have different shapes, sizes, and the like, so that, for example, the organic compounds from the first evaporation source 202 and the third evaporation source 204 are directed over a wide area, whereas the organic compounds from the second evaporation source 203 are directed over a narrow area. Alternatively, the opening regions 223 of the evaporation sources can be oriented in different directions, as shown in Fig. 4A is shown.

[0154] Inside the vacuum chamber 211, one or more substrates, preferably two or more substrates (in Fig. 2A, substrates 205 to 207) are arranged and moved from left to right at a suitable speed (i.e., in a substantially perpendicular direction to the orientation of the opening regions 223 of the evaporation sources), as shown. It should be noted that the evaporation sources may have different distances to the substrates 205 to 207.

[0155] In the Fig. In the manufacturing apparatus shown in Figure 4A, the n-type host vaporized by the first vaporization source 202 is mainly deposited in a region designated by reference numeral 208. In a region designated by reference numeral 209, the n-type host vaporized by the first vaporization source 202, the gas vaporized by the second vaporization source 203, and the p-type host vaporized by the third vaporization source 204 are deposited in a specific ratio. Furthermore, in a region designated by reference numeral 210, the p-type host vaporized by the third vaporization source 204 is mainly deposited.

[0156] Accordingly, as substrates 205 to 207 are moved from right to left, first the n-type host layer 103 is formed, then the light-emitting layer 102 is formed, and subsequently the p-type host layer 104 is formed. In some cases, the n-type transition zone 106 is formed between the n-type host layer 103 and the light-emitting layer 102, and the p-type transition zone 107 is formed between the p-type host layer 104 and the light-emitting layer 102, as with light-emitting element 101b. In other cases, as with light-emitting element 101c, no clear boundary is formed between the light-emitting layer and the p-type or n-type host layer.

[0157] One in the Fig. The manufacturing device shown in 4B is obtained by the Fig. The manufacturing apparatus shown in Figure 4A is modified. That is, the manufacturing apparatus comprises a first evaporation source 212, a second evaporation source 213, a third evaporation source 214, a fourth evaporation source 215, and a fifth evaporation source 216 in a vacuum chamber 211. Here, the first evaporation source 212 and the second evaporation source 213 evaporate the n-type host; the third evaporation source 214 causes the guest to evaporate; and the fourth evaporation source 215 and the fifth evaporation source 216 cause the p-type host to evaporate.

[0158] As in the case of the in Fig. In the manufacturing apparatus shown in Figure 4A, the opening areas 223 of the evaporation sources can have different shapes, sizes, and the like, be arranged in different positions, or be oriented in different directions. Inside the vacuum chamber 211, one or more substrates, preferably two or more substrates (in Fig. 2B, substrates 217 to 217) are arranged and moved from left to right at a suitable speed, as shown.

[0159] At the in Fig. In the manufacturing apparatus shown in Figure 4B, the n-type host vaporized by the first vaporization source 212 is mainly deposited in a region designated by reference numeral 220. In a region designated by reference numeral 221, the n-type host vaporized by the second vaporization source 213, the gas vaporized by the third vaporization source 214, and the p-type host vaporized by the fourth vaporization source 215 are deposited in a specific ratio. Furthermore, in a region designated by reference numeral 222, the p-type host vaporized by the fifth vaporization source 216 is mainly deposited.

[0160] The in Fig. The manufacturing apparatus shown in Figure 4B can provide drastic concentration changes at the interface between the light-emitting layer 102 and the host layer 103 of the n type and at the interface between the light-emitting layer 102 and the host layer 104 of the p type, as in the light-emitting element 101a. (Version 4)

[0161] In this embodiment, 2mDBTPDBq-II, which can be used as an n-type host, PCBNBB, which can be used as a p-type host, and an exciplex thereof are described. Table 1 shows the essential physical properties of 2mDBTPDBq-II, PCBNBB, and [Ir(dppm)2(acac)] and [Ir(mppr-Me)2(dpm)], which are suitable guest materials when 2mDBTPDBq-II and PCBNBB are used. (Table 1) substance LUMO-(eV) HOMO level (eV) T1 level (eV) 2mDBTPDBq-II -2,78 -5,88 2,54 PCBNBB -2,31 -5,46 2,40 [Ir(dppm)2(acac)] -2,98 -5,56 2,22 [Ir(mppr-Me)2(dpm)] -2,77 -5,50 2,26

[0162] In a region where 2mDBTPDBq-II and PCBNBB are mixed, the LUMO level is -2.78 eV and the HOMO level is -5.46 eV. These levels correspond to the LUMO and HOMO levels of an exciplex of 2mDBTPDBq-II and PCBNBB, respectively. Additionally, the LUMO and HOMO levels of [Ir(mppr-Me)2(dpm)], which is the guest material, are essentially the same.

[0163] On the other hand, both the LUMO and HOMO levels of [Ir(dppm)2(acac)] are lower than those above, so it has been found that [Ir(dppm)2(acac)] tends to capture electrons. This shows that the probability of direct recombination is higher when [Ir(dppm)2(acac)] is used as the guest than when [Ir(mppr-Me)2(dpm)] is used.

[0164] Additionally, the energy level (T1 level) of each of [Ir(mppr-Me)2(dpm)] and [Ir(dppm)2(acac)] in the excited triplet state is 0.1 eV or more lower than the energy level of each of 2mDBTPDBq-II and PCBNBB in the excited triplet state. Therefore, the probability that [Ir(mppr-Me)2(dpm)] or [Ir(dppm)2(acac)] in the excited triplet state will transfer its state to the excited triplet state of 2mDBTPDBq-II or PCBNBB is low. In particular, the T1 level of [Ir(dppm)2(acac)] is 0.18 eV or more lower, indicating that [Ir(dppm)2(acac)] has a higher emission efficiency than [Ir(mppr-Me)2(dpm)].

[0165] Fig. 5A shows a molecular structure of Fig. 5A 2mDBTPDBq-II. In general, when a heteroatom (i.e., an atom with a higher electronegativity than carbon), such as a nitrogen atom, is introduced to the constituent atoms of a six-membered aromatic ring, such as a benzene ring, the heteroatom attracts the π electrons to the ring, and the ring tends to become electron-deficient. In the diagram, an area A surrounded by a dotted line corresponds to a region exhibiting π-electron deficiency, and this region tends to capture electrons. Heteroaromatic compounds comprising six-membered rings tend to act as n-type hosts.

[0166] Fig. Figure 5B shows a molecular structure of PCBNBB. In general, when a nitrogen atom located outside an aromatic ring, such as a benzene ring, is bonded to the ring, it donates a lone pair of electrons, creating an electron surplus and a tendency to donate electrons (i.e., to capture holes). In the diagram, region B, surrounded by a dotted line, corresponds to a region with an excess of π electrons, and this region tends to donate electrons (or capture holes). Aromatic amine compounds tend to act as p-type hosts.

[0167] There are relatively large gaps of 0.47 eV between the LUMO levels and 0.42 eV between the HOMO levels of 2mDBTPDBq-II and PCBNBB. These gaps act as barriers for the electrons and holes and can prevent the carriers, which do not recombine, from penetrating the light-emitting layer. The height of such a barrier is preferably 0.3 eV or more, more preferably 0.4 eV or more.

[0168] Whether an n-type and a p-type host form an exciplex can be determined by measuring photoluminescence. If the photoluminescence spectrum of an exciplex overlaps with the absorption spectrum of a guest, it can be said that the energy transfer process is likely due to the Förster mechanism.

[0169] The Fig. 6A and Fig. Figure 6B shows a UV absorption spectrum (absorption spectrum 0) of a dichloromethane solution of [Ir(dppm)2(acac)]. The absorption spectrum was measured at room temperature using a UV light spectrophotometer (V-550, manufactured by JASCO Corporation) in the state in which the dichloromethane solution (0.093 mmol / l) was introduced into a quartz cell at room temperature.

[0170] Additionally, the Fig. 6A and Fig. Figure 6B also shows a photoluminescence spectrum of a thin film made of 2mDBTPDBq-II (emission spectrum 1), a photoluminescence spectrum of a thin film made of PCBNBB (emission spectrum 2), and a photoluminescence spectrum of a thin film made of a mixed material of 2mDBTPDBq-II and PCBNBB (emission spectrum 3). The ratio of PCBNBB to 2mDBTPDBq-II in the thin film of the mixed material was 0.8:0.2.

[0171] In Fig. 6A represents the wavelength (nm) on the horizontal axis and the molar absorption coefficient ε (M) on the vertical axis. -1 ·cm -1 ) and the emission intensity (arbitrary unit). In Fig. 6B, the horizontal axis represents the energy (eV) and the vertical axis represents the molar absorption coefficient ε (M -1 ·cm -1 ) and the emission intensity (arbitrary unit).

[0172] From the absorption spectrum 0 in Fig. Figure 6A shows that [Ir(dppm)2(acac)] has a broad absorption band at approximately 520 nm. This absorption band is thought to be essential for light emission.

[0173] Emission spectrum 3 shows a peak at a longer wavelength (lower energy) than emission spectra 1 and 2. Additionally, the peak of emission spectrum 3 is closer to the absorption band of [Ir(dppm)2(acac)] than the peaks of emission spectra 1 and 2. In particular, the difference between the peak of absorption spectrum 0 of [Ir(dppm)2(acac)] and the peak of emission spectrum 3 is 0.02 eV.

[0174] It has been found that the emission spectrum of the mixed material of 2mDBTPDBq-II and PCBNBB exhibits a peak at a longer wavelength (lower energy) than the emission spectrum of either organic compound alone. This indicates that an exciplex is formed by mixing 2mDBTPDBq-II with PCBNBB. Furthermore, no peak originating from either 2mDBTPDBq-II or PCBNBB is observed, meaning that even when 2mDBTPDBq-II and PCBNBB are excited separately, they immediately form an exciplex.

[0175] The peak of the emission spectrum of the mixed material shows a large overlap with the absorption band in the absorption spectrum 0 of [Ir(dppm)2(acac)], which is thought to contribute significantly to light emission. This suggests that a light-emitting element containing 2mDBTPDBq-II, PCBNBB, and [Ir(dppm)2(acac)] exhibits high energy transfer efficiency from an exciplex to a guest molecule. (Example 1)

[0176] In this example, a light-emitting element of an embodiment of the present invention was fabricated and its performance was verified. In the light-emitting element of this example, 2DBTPDBq-II was used as an n-type host and PCBA1BP was used as a p-type guest.

[0177] The light-emitting element produced in this example has a layered structure consisting of a cathode, an electron injection layer, an electron transport layer, a first layer (an n-type host layer), a light-emitting layer (a layer containing the n-type host and the p-type host), a second layer (a p-type host layer), a hole injection layer, and an anode, in that order from top to bottom on a substrate.

[0178] The chemical formulas (structural formulas) of the materials used in this example, including those mentioned above, are shown below. It should be noted that the chemical formulas of the materials already described above have been omitted.

[0179] A method for fabricating the light-emitting element of this example is described below. First, a film of indium tin oxide containing silicon dioxide (ITSO) was formed on a glass substrate by sputtering, thus creating the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0180] Subsequently, as a pretreatment to form the light-emitting element on the substrate, a UV-ozone treatment was performed for 370 seconds after washing one surface of the substrate with water, followed by baking or firing at 200 °C for one hour. The substrate was then placed in a vacuum evaporation device, where the pressure was reduced to approximately 10 -4 Pa was reduced, and was subjected to vacuum baking at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate was cooled for approximately 30 minutes.

[0181] The substrate, supplied with the anode, was then attached to a substrate holder in the vacuum evaporation apparatus, such that the surface on which the anode was positioned faced downwards. Subsequently, DBT3P-II and molybdenum(VI) oxide were evaporated under a reduced pressure of approximately 10 -4 Pa co-evaporates to form the hole injection layer on the anode. The thickness of the hole injection layer was set to 40 nm and the weight ratio of DBT3P-II to molybdenum oxide was set to 4:2 (=DBT3P-II : molybdenum oxide).

[0182] Subsequently, a second layer of PCBA1BP with a thickness of 20 nm was formed on the hole injection layer by an evaporation process.

[0183] Furthermore, PCBA1BP, 2DBTPDBq-II, and [Ir(dppm)2(acac)] were co-evaporated to form a light-emitting layer on the second layer. The weight ratio of 2DBTPDBq-II to PCBA1BP and [Ir(dppm)2(acac)] was adjusted to 0.8:0.2:0.05. The thickness of the light-emitting layer was set to 40 nm.

[0184] Furthermore, a film of 2mDBTPDBq-II with a thickness of 10 nm was formed on the light-emitting layer by an evaporation process to form the first layer.

[0185] Then, a film of bathophene anthroline (abbreviation: BPhen) with a thickness of 20 nm was formed on the first layer to create the electron transport layer.

[0186] Furthermore, a film of lithium fluoride (LiF) with a thickness of 1 nm was formed on the electron transport layer by evaporation to create an electron injection layer.

[0187] Finally, an aluminum film with a thickness of 200 nm was formed as the cathode by evaporation. In this way, the light-emitting element was produced. It should be noted that in all the above evaporation steps, the evaporation was carried out using a resistance heating process. Table 2 shows the element structure of the light-emitting element obtained as described above. (Table 2) anode Hole injection layer Second shift Light-emitting layer ITSO DBT3P-II:MoO x PCBA1BP 2DBTPDBq-II:PCBA1BP:[Ir(dppm)2(acac)] (4:2) (0,8:0,2:0,05) 110 nm 40 nm 20 nm 40 nm (Table 2 continued) First shift electron transport layer Electron injection layer cathode 2DBTPDBq-II BPhen LiF Al 10 nm 20 nm 1 nm 200 nm

[0188] The light-emitting element was sealed in a glove box containing a nitrogen atmosphere to prevent exposure to air. The element's operating characteristics were then measured. It should be noted that the measurements were performed at room temperature (in an atmosphere maintained at 25 °C).

[0189] Fig. Figure 7A shows the dependence of the current density on the luminance of the resulting light-emitting element. Fig. Figure 7B shows the dependence of voltage on luminance and Fig. Figure 7C shows the dependence of luminance on current efficiency. Table 3 shows the essential characteristics or properties of the resulting light-emitting element. The voltage required to achieve a luminance of approximately 1000 cd / m² 2 The voltage required to obtain is extremely low (2.6 V). The resulting light-emitting element has a power efficiency of 70% or more and is very efficient. (Table 3) Tension Current density Color value components Luminance Power output (V) (mA / cm 2 ) (x, y) (cd / m 2 ) (cd / A) 2,6 1,88 (0,56, 0,44) 1154 61,5 (Table 3 continued) Energy efficiency (Im / W) External quantum efficiency (%) Energy efficiency (%) 74,3 24,5 19,3 (Example 2)

[0190] In this example, a light-emitting element of an embodiment of the present invention was fabricated and measured. In this example, a light-emitting element was fabricated using 2mDBTPDBq-II as an n-type host and PCBA1BP as a p-type guest.

[0191] The light-emitting element produced in this example has the same layered structure as the light-emitting element in Example 1. The materials described above were used. Furthermore, a fabrication process similar to that in Example 1 was employed, except that the host is different from the n-type (i.e., 2DBTPDBq-II from Example 1 was simply replaced by 2mDBTPDBq-II); therefore, the details are omitted here. A structure of 2mDBTPDBq-II is shown below.

[0192] Table 4 shows the element structure of the obtained light-emitting element. (Table 4) anode Hole injection layer Second shift Light-emitting layer ITSO DBT3P-II:MoOx PCBA1BP 2mDBTPDBq-II:PCBA1BP:[Ir(dppm)2(acac)] (4:2) (0,8:0,2:0,05) 110 nm 40 nm 20 nm 40 nm (Table 4 continued) First shift electron transport layer Electron injection layer cathode 2mDBTPDBq-II BPhen LiF Al 10 nm 20 nm 1 nm 200 nm

[0193] Fig. Figure 8A shows the dependence of the current density on the luminance of the resulting light-emitting element. Fig. Figure 8B shows the dependence of voltage on luminance and Fig. Figure 8C shows the dependence of luminance on current efficiency. Table 5 shows the essential characteristics of the resulting light-emitting element. The voltage required to produce a luminance of approximately 1000 cd / m² 2 The required voltage is extremely low (2.7 V). The resulting light-emitting element exhibits an external quantum efficiency of 25% or more and is highly efficient. It has been found that the upper limit of the external quantum efficiency of conventional light-emitting elements is approximately 20%, due to light extraction efficiency. However, the GCCH concept allows the formation of a light-emitting element with an external quantum efficiency exceeding 25%. (Table 5) Tension Current density Color value components Luminance Power output (V) (mA / cm 2 ) (x, y) (cd / m 2 ) (cd / A) 2,7 1,35 (0,57, 0,43) 845 62,6 (Table 5 continued) Energy efficiency (Im / W) External quantum efficiency (%) Energy efficiency (%) 72,9 25,5 19,3 Explanation of reference symbols

[0194] 101: light-emitting element, 101a: light-emitting element, 101b: light-emitting element, 101c: light-emitting element, 102: light-emitting layer, 103: n-type host layer, 104: p-type host layer, 105: guest molecule, 106: n-type transition region, 107: p-type transition region, 108: cathode, 109: anode, 110: EL layer, 110a: EL layer, 110b: EL layer, 111: electron transport layer, 112: hole transport layer, 113: electron injection layer, 114: hole injection layer, 115: charge generation layer, 116: electron injection buffer layer, 117: electron relay layer 118: Composite material layer, 201: Vacuum chamber, 202: First evaporation source, 203: Second evaporation source, 204: Third evaporation source, 205: Substrate, 206: Substrate, 207: Substrate, 211: Vacuum chamber, 212: First evaporation source, 213: Second evaporation source, 214: Third evaporation source, 215: Fourth evaporation source, 216: Fifth evaporation source, 217: Substrate218: Substrate, 219: Substrate and 223: Opening area.< / elektroplex>

Claims

[1] Light-emitting element (101), comprising: a first electrode; a first layer above the first electrode, wherein the first layer contains a first organic compound with a hole transport property; a light-emitting layer (102) above the first layer, wherein the light-emitting layer contains the first organic compound, a second organic compound with an electron transport property and a compound with a light-emitting property; a second layer above the light-emitting layer (102), wherein the second layer contains the second organic compound; and a second electrode above the second layer, wherein the first organic compound and the second organic compound are chosen to form an exciplex, where a triplet excitation level of the first organic compound and a triplet excitation level of the second organic compound are higher than a triplet excitation level of the compound with a light-emitting property, wherein the compound is configured with a light-emitting property to convert energy of the triplet excitation level of the compound into light emission, and where the LUMO level of the compound with a light-emitting property is lower than the LUMO level of the first organic compound and the second organic compound. [2] Light-emitting element (101), comprising: a first electrode; a first electroluminescent layer over the first electrode; a charge-generating layer (115) above the first electroluminescent layer; a second electroluminescent layer above the charge generation layer (115), and a second electrode above the second electroluminescent layer, comprising at least one of the first electroluminescent layer and the second electroluminescent layer: a first layer on the side of the first electrode, wherein the first layer contains a first organic compound with a hole transport property; a light-emitting layer (102) above the first layer, wherein the light-emitting layer (102) contains the first organic compound, a second organic compound with an electron transport property, and a compound with a light-emitting property; and a second layer above the light-emitting layer (102), wherein the second layer contains the second organic compound, wherein the first organic compound and the second organic compound are chosen such that they form an exciplex, where a triplet excitation level of the first organic compound and a triplet excitation level of the second organic compound are higher than a triplet excitation level of the compound with a light-emitting property, wherein the compound is configured with a light-emitting property to convert energy of the triplet excitation level of the compound into light emission, and where the LUMO level of the compound with a light-emitting property is lower than the LUMO level of the first organic compound and the second organic compound. [3] Light-emitting element (101) according to claim 1 or 2, further comprising a hole injection layer (114) between the first layer and the first electrode. [4] Light-emitting element (101) according to claim 3, further comprising a hole transport layer (112) between the first layer and the hole injection layer (114). [5] Light-emitting element (101) according to claim 1 or 2, further comprising an electron injection layer (113) between the second electrode and the second layer. [6] Light-emitting element (101) according to claim 5, further comprising an electron transport layer (111) between the second electrode and the electron injection layer (113). [7] Light-emitting element (101) according to claim 1 or 2, wherein the compound with a light-emitting property comprises an organometallic complex. [8] Light-emitting element (101) according to claim 7, wherein the organometallic complex contains iridium. [9] Light-emitting element (101) according to claim 1 or 2, wherein the first organic compound is an aromatic amine or a carbazole derivative. [10] Light-emitting element (101) according to claim 1 or 2, wherein the second organic compound has a heteroaromatic ring. [11] Light-emitting element (101) according to claim 2, wherein one of the first electroluminescent layer and the second electroluminescent layer emits fluorescence and the other of the first electroluminescent layer and the second electroluminescent layer emits phosphorescence. [12] Light-emitting element (101) according to claim 2, wherein the first electroluminescent layer and the second electroluminescent layer emit phosphorescence. [13] Light-emitting element (101) according to claim 1 or 2, wherein the first layer further contains the second organic compound, and wherein the concentration of the second organic compound in the first layer changes in a direction from the first electrode to the light-emitting layer (102). [14] Light-emitting element (101) according to claim 1 or 2, the second layer further contains the first organic compound, and wherein the concentration of the first organic compound in the second layer changes in a direction from the second electrode to the light-emitting layer. [15] Light-emitting element (101) according to claim 1 or 2, wherein in the light-emitting layer (102) a concentration of the first organic compound and a concentration of the second organic compound change in a direction from the first layer to the second layer. [16] Light-emitting element (101) according to claim 1 or 2, wherein an absorption band of the compound with a light-emitting property, which is located on the side of the longest wavelength lies, overlapping with an emission of the exciplex. [17] Electronic device comprising the light-emitting element (101) according to claim 1 or 2. [18] Lighting device comprising the light-emitting element (101) according to claim 1 or 2.

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