Light-emitting device

Abstract

To provide a light emitter with high external quantum efficiency.SOLUTION: A light emitter includes a light emitting layer 102 including an N-type host and a P-type host between a pair of electrodes, and forms a first layer (N-type host layer 103) between the light emitting layer 102 and a negative electrode, and a second layer (P-type host layer 104) between the light emitting layer 102 and a positive electrode. There is not energy barrier when infusing an electron and a positive hole into the light emitting layer 102. On the other hand, there is the energy barrier in a middle when orienting the electron to a positive electrode or a positive hole to the negative electrode, and the electron and the positive hole are confined to the light emitting layer. Therefore, energy utilization efficiency is increased. A region where the concentration of the N-type host and the P-type host is continuously changed may be provided between the N-type host layer 103 and the light emitting layer 102, or the P-type host layer 104 and the light emitting layer 102.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Research and development of organic EL elements is being actively carried out. The basic structure of an organic EL element is as follows: A layer containing a light-emitting organic compound (hereinafter referred to as a light-emitting layer) is sandwiched between a pair of electrodes. , can be made thinner and lighter, can respond quickly to input signals, can be driven by low DC voltage, etc. Due to its characteristics, it is attracting attention as a next-generation flat panel display element. Displays using such light-emitting elements have excellent contrast and image quality, and a wide viewing angle. Furthermore, since organic EL elements are surface light sources, they are also suitable for LCD displays. Applications as a light source for backlighting and illumination are also being considered.

[0003] The light-emitting mechanism of organic EL elements is a carrier injection type. In other words, the light-emitting layer is sandwiched between electrodes. By applying a voltage, electrons and holes injected from the electrode recombine to form a light-emitting material. The excited state is reached, and light is emitted when the excited state returns to the ground state. The excited state can be a singlet excited state or a triplet excited state. The statistical production ratio of the former is thought to be one-third of the latter.

[0004] In light-emitting organic compounds, the ground state is usually a singlet state. Emission from the triplet state is called fluorescence because it is an electron transition between the same spin multiplicity states. Emission from the excited state is called phosphorescence because it is an electron transition between different spin multiplicities. Here, a compound that emits fluorescence (hereinafter referred to as a fluorescent compound) usually emits phosphorescence at room temperature. Therefore, in a light-emitting device using a fluorescent compound, only fluorescence is observed. The theoretical limit of the internal quantum efficiency (the ratio of photons generated to injected carriers) is It is set at 25% based on the ratio of the singlet excited state to the triplet excited state mentioned above.

[0005] On the other hand, if a compound that emits phosphorescence (hereinafter referred to as a phosphorescent compound) is used, the internal quantum The efficiency can be increased to 100%, which means that the luminescence is higher than that of fluorescent compounds. For this reason, in order to realize a highly efficient light-emitting device, In recent years, development of light-emitting elements using phosphorescent compounds has been actively pursued.

[0006] In particular, phosphorescent compounds with iridium as the central metal are popular due to their high phosphorescent quantum efficiency. Organometallic complexes with iridium as the central metal have been attracting attention. An organometallic complex of the formula (I) is disclosed as a phosphorescent material.

[0007] When the light-emitting layer of the light-emitting element is formed using the above-mentioned phosphorescent compound, the concentration quenching of the phosphorescent compound is To suppress quenching by light and triplet-triplet annihilation, the compound is placed in a matrix of other compounds. In this case, the compound that becomes the matrix is ​​formed so that the phosphorescent compound is dispersed in the matrix. The substance is called the host, and the compound dispersed in the matrix, such as a phosphorescent compound, is called the guest. .

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

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

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

[0011] (2) When electrons and holes recombine in the host molecule, the host molecule enters an excited state ( energy transfer process). (2-1) When the excited state of the host molecule is a triplet excited state The triplet excited energy level (T1 level) of the host molecule is higher than the T1 level of the guest molecule. When the excitation energy is high, the guest molecule undergoes triplet excitation. The guest molecule in the triplet excited state emits phosphorescence. The reverse energy transfer to the triplet excited energy level (T1 level) must also be considered. Therefore, the T1 level of the host molecule must be higher than the T1 level of the guest molecule. be. (2-2) When the excited state of the host molecule is a singlet excited state If the S1 level of the host molecule is higher than the S1 and T1 levels of the guest molecule, the host Excitation energy is transferred from the molecule to the guest molecule, and the guest molecule enters a singlet excited state or a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. The guest molecule in this state undergoes intersystem crossing to a triplet excited state and emits phosphorescence.

[0012] In other words, in the energy transfer process (2) above, the triplet excitation energy of the host molecule It is important not only to transfer the singlet excitation energy to the guest molecule efficiently, but also to transfer the singlet excitation energy to the guest molecule efficiently. This becomes:

[0013] Considering this energy transfer process, excitation energy is transferred from the host molecule to the guest molecule. Before this happens, the host molecule itself is deactivated, releasing its excitation energy as light or heat. This will result in a decrease in luminous efficiency.

[0014] <Energy transfer process> The energy transfer process between molecules is described in detail below.

[0015] First, the following two mechanisms have been proposed for intermolecular energy transfer: The molecule that provides the excitation energy is the host molecule, and the molecule that receives the excitation energy is the is referred to as the guest molecule.

[0016] <Förster mechanism (dipole-dipole interaction)> The Förster mechanism does not require direct contact between molecules for energy transfer. Energy transfer occurs through the resonance phenomenon of dipole vibration between the molecule and the guest molecule. The host molecule transfers energy to the guest molecule through the vibrational resonance phenomenon, and the host molecule The guest molecule enters the excited state. The rate constant of the Förster mechanism is k h * →g of This is shown in equation (1).

[0017]

number

[0018] In formula (1), ν represents the frequency, and f' h (ν) is the normalized emission of the host molecule Spectra (fluorescence spectrum when discussing energy transfer from singlet excited states, triplet represents the phosphorescence spectrum when discussing energy transfer from the first excited state, and ε g (ν) is represents the molar extinction coefficient of the guest molecule, N represents Avogadro's number, and n represents the refractive index of the medium. R represents the intermolecular distance between the host molecule and the guest molecule, and τ represents the measured lifetime of the excited state (fluorescence represents the lifetime and phosphorescence lifetime), c represents the speed of light, and φ represents the luminescence quantum efficiency (singlet excitation When discussing energy transfer from a triplet excited state, the fluorescence quantum efficiency is When discussing phosphorescence, K 2 is the transition pair of the host molecule and the guest molecule. Coefficient (0 to 4) that represents the orientation of the polar moment. In the case of random orientation, K 2 = It's 2 / 3.

[0019] Dexter mechanism (electron exchange interaction) The Dexter mechanism occurs when the host and guest molecules approach the effective contact distance where orbital overlap occurs. The energy is transferred through the exchange of electrons of the excited host molecule and the ground state guest molecule. -Transfer occurs. The rate constant of the Dexter mechanism is k h * →g is shown in equation (2).

[0020]

number

[0021] In equation (2), h is Planck's constant, and K is a constant with the dimension of energy. , ν represents the frequency, and f' h (ν) is the normalized emission spectrum (singlet When discussing energy transfer from excited states, the fluorescence spectrum is used, and when discussing energy transfer from triplet excited states, the When discussing energy transfer, ε' represents the phosphorescence spectrum, and g (ν) is the standard of the guest molecule where L is the effective molecular radius, and R is the ratio of the host molecule to the guest molecule. represents the intermolecular distance.

[0022] Here, the energy transfer efficiency from the host molecule to the guest molecule Φ ET is expressed by equation (3). It is thought that r is the emission process of the host molecule (emission from the singlet excited state of the host molecule). When discussing energy transfer, consider the energy transfer from the triplet excited state of the fluorescence or host molecule. represents the rate constant of the reaction (phosphorescence, if discussed), and k n is the rate constant for non-radiative processes (thermal deactivation and intersystem crossing) represents the number, and τ represents the observed excited state lifetime of the host molecule.

[0023]

number

[0024] First, from equation (3), the energy transfer efficiency Φ ET To increase the The rate constant k h * →g , other competing rate constants k r +k n (=1 / τ) The rate constant of the energy transfer, k h* →g Large In order to achieve this, from equations (1) and (2), the Förster mechanism and the Dexter mechanism In both of these mechanisms, the emission spectrum of the host molecule (energy from the singlet excited state) When discussing energy transfer, consider the fluorescence spectrum and energy transfer from triplet excited states. The phosphorescence spectrum in the case of a triplet) and the absorption spectrum of the guest molecule (usually phosphorescence, so It can be seen that a larger overlap with the energy difference between the excited state and the ground state is better. [Prior art documents] [Patent documents]

[0025] [Patent Document 1] International Publication No. 2000 / 070655 [Patent Document 2] U.S. Patent No. 7,572,522 Summary of the Invention [Problem to be solved by the invention]

[0026] As described above, by using a phosphorescent compound, a highly efficient light-emitting element can be obtained. Considering the energy transfer process, in order to realize a highly efficient light-emitting device, it is necessary to It is necessary to increase the overlap between the absorption spectrum of the guest molecule and the absorption spectrum of the ion beam. , to suppress the reverse energy transfer from the T1 level of the guest molecule to the T1 level of the host molecule. In addition, the T1 level of the host molecule must be higher than the T1 level of the guest molecule.

[0027] Generally, organometallic complexes (e.g., iridium complexes) used as phosphorescent guest molecules are Triplet MLCT (Metal to Ligand Charge) is applied to relatively long wavelength regions. The absorption due to the (transfer) transition is also evident from the excitation spectrum. It can be said that absorption in the wavelength region (mainly around 450 nm) contributes greatly to the emission of guest molecules. Therefore, there is a large overlap between the absorption in this long wavelength region and the phosphorescence spectrum of the host molecule. This is preferable because efficient energy transfer occurs from the triplet excited state of the host molecule, This is because the triplet excited state of the guest molecule is efficiently generated.

[0028] On the other hand, since the S1 level of the host molecule is higher than the T1 level, the fluorescence spectrum corresponding to the S1 level The toll is observed in a much shorter wavelength region compared to the phosphorescence spectrum corresponding to the T1 level. This means that the fluorescence spectrum of the host molecule and the long wavelength absorption of the guest molecule (triple This means that the overlap with the absorption due to the MLCT transition is small. This means that the energy transfer from the singlet excited state of the molecule to the guest molecule is not fully utilized. .

[0029] That is, in conventional phosphorescent light-emitting devices, the host molecule is converted into a phosphorescent guest molecule from a singlet excited state. energy transfer to generate an excited singlet state, followed by intersystem crossing to generate a phosphorescent compound The probability of undergoing the process of generating a triplet excited state is extremely low.

[0030] The present invention has been made in view of such problems, and one aspect of the present invention is a new principle Another embodiment of the present invention is a light-emitting element having high external quantum efficiency. to provide. [Means for solving the problem]

[0031] One embodiment of the present invention is a method for producing a phosphorescent compound (guest), a first organic compound, and a second organic compound. The light-emitting layer is disposed between a pair of electrodes (a first electrode and a second electrode), and the light-emitting layer and the second electrode are disposed between the first electrode and the second electrode. Between the first and second electrodes, a layer containing the first organic compound but not the second organic compound (the first organic compound) is formed. The first layer is formed on the light-emitting layer, and the second electrode is provided with a second organic compound between the light-emitting layer and the second electrode. The light-emitting element has a layer (second layer) that does not contain the organic compound (1).

[0032] In the above, the first organic compound has electron transporting properties superior to hole transporting properties, and the second organic compound has The hole transporting property of the organic compound is superior to the electron transporting property. The organic compound is a material that forms an exciplex. The guest is excited via energy transfer from the exciplex to the guest, and the guest is excited. Light emission from the layer other than the light-emitting layer is obtained. You may do so.

[0033] The exciplex is formed when the difference between the singlet excitation energy and the triplet excitation energy is extremely small. In other words, the emission from the singlet state of the exciplex and the emission from the triplet state The emission occurs in a very close wavelength range. The triplet ML of phosphorescent compounds that appear in the long wavelength region is observed on the longer wavelength side compared to the triplet ML of phosphorescent compounds that appear in the long wavelength region. The overlap between the absorption due to the CT transition and the emission from the exciplex can be increased. This means that phosphorus can be released from both the singlet and triplet states of the exciplex. This means that energy can be transferred efficiently to the photoactive compound, improving the efficiency of light-emitting devices. This will contribute to

[0034] Furthermore, there is no ground state in the exciplex. Therefore, the triplet state of the guest molecule Since there is no reverse energy transfer process from the exciplex to the host molecule, This process does not cause a decrease in the efficiency of the light emitting device.

[0035] In this specification, the electron transporting or hole transporting properties of the first organic compound and the second organic compound are The first organic compound and the second organic compound were selected from N-type phosphatase inhibitors. Either the N-type host or the P-type host is a material that emits fluorescence. The ratio of the N-type host to the P-type host in the light-emitting layer may be It is preferably 10% or more.

[0036] Between the first layer and the light-emitting layer or between the second layer and the light-emitting layer, the ratio of N-type host to P-type host is In addition, in the light-emitting layer, a region in which the N-type host The ratio of the P-type host to the P-type host may be set to vary continuously.

[0037] Another aspect of the present invention is a layer of an N-type host containing an N-type host and a layer of a P-type host containing a P-type host. The gate is sandwiched between a layer of N-type host and a layer of P-type host, and the gate is sandwiched between the N-type host and the P-type host. and a material having a region having an N-type host and a P-type host, and wherein the N-type host and the P-type host form an exciplex. The light-emitting element is characterized in that the material is a luminescent material.

[0038] In the light-emitting element, the phosphorescent compound is preferably an organometallic complex. The photoactive compound may be present in the first layer or the second layer in addition to the light-emitting layer, or in the light-emitting layer and the first layer. The second layer may be included in the region between the first layer and the second layer, or in the region between the light-emitting layer and the second layer.

[0039] In one aspect of the present invention, the light-emitting layer has an N-type host molecule, a P-type host molecule, and a guest molecule. Of course, the molecules do not have to be regularly arranged and may be in a state with extremely little regularity. Particularly when the light-emitting layer is a thin film of 50 nm or less, it preferably becomes an amorphous state. Therefore, it is preferable to select a combination of materials that are difficult to crystallize. Also, the N-type host layer and the P-type host layer may be composed of two or more different compounds.

[0040] The light-emitting device of one aspect of the present invention can be applied to a light-emitting device, an electronic device, and a lighting device.

Effects of the Invention

[0041] In an appropriate combination of an N-type host and a P-type host, an exciplex is formed when in an excited state. The necessary condition for forming an exciplex is that the HOMO level of the N-type host < the HOMO level of the P-type host < the LUMO level of the N-type host < the LUMO level of the P-type host. However, this is not a sufficient condition. For example, Alq3 and NPB satisfy the above conditions but do not form an exciplex. On the other hand, when an N-type host and a P-type host can form an exciplex, as described above, energy transfer occurs from both the singlet state and the triplet state of the exciplex to the guest molecule, and thus it is possible to excite the guest molecule. Therefore, the light-emitting efficiency is improved compared to conventional phosphorescent devices.

[0042] By the way, in a light-emitting device, when there is a junction between different layers, an energy gap exists at the interface.

[0043] This causes a loop, which increases the driving voltage and reduces the power efficiency (see Patent Document 2). It is preferable to minimize the joining of different materials in the light emitting device.

[0044] In any of the above embodiments, an emitting compound containing a mixture of an N-type host and a P-type host is used, as described below. The interface between the N-type host and the N-type layer acts as a barrier to holes, but is almost completely blocked by electrons. There is no obstacle, and the interface between the light-emitting layer and the P-type host layer acts as a barrier to electrons, There is almost no obstacle for holes. Therefore, electrons and holes can pass through the light-emitting layer or the N-type hole. As a result, electrons are trapped between the P-type host layer and the P-type host layer. This also prevents holes from reaching the negative electrode, improving the luminous efficiency. Generally, a glass fiber gives a broad emission spectrum. The emission of the fluorine molecule results in a narrow half-width spectrum, resulting in high color purity of the emission. A high-performance light-emitting device can be obtained. [Brief explanation of the drawings]

[0045] [Figure 1] 1 is a conceptual diagram of the present invention. [Figure 2] 1A and 1B are diagrams illustrating the principle of the present invention. [Figure 3] 1A to 1C are diagrams illustrating an example of an embodiment of the present invention. [Figure 4] 1A to 1C are diagrams illustrating an example of an embodiment of the present invention. [Figure 5] 1A to 1C are diagrams illustrating an example of an embodiment of the present invention. [Figure 6] 1A to 1C are diagrams illustrating an example of an embodiment of the present invention. [Figure 7] FIG. 2 is a graph showing characteristics of a light-emitting element obtained in Example 1. [Figure 8] 10A and 10B are graphs illustrating characteristics of the light-emitting element obtained in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0046] The embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description. The present invention is not limited to the above embodiments, and various changes and modifications may be made in the form and details thereof without departing from the spirit and scope of the present invention. It will be readily understood by those skilled in the art that the present invention can be achieved by the following embodiments. It should not be construed as being limited to the contents of the description. The same reference numerals are used in different drawings to denote the same parts or parts having similar functions. A repeated explanation will be omitted.

[0047] (Embodiment 1) As shown in FIG. 1(A), a light emitting device 101a according to an example of this embodiment is an N-type host. A layer 103 of an N-type host containing a P-type host, a layer 104 of a P-type host containing a P-type host, and A layer having both an N-type host and a P-type host sandwiched therebetween (hereinafter referred to as the light-emitting layer 102) The light-emitting layer 102 has guest molecules 105 dispersed therein.

[0048] FIG. 1B shows the concentration of the N-type host (denoted as N in the drawing) and the P-type The distribution of the host concentration (denoted as P in the figure) is shown. In O2, the concentration of N-type host is 80% and the concentration of P-type host is 20%. In the optical layer 102, the ratio of N-type host to P-type host is 4:1. The thickness of the N-type host should be determined taking into consideration the transport properties of the N-type host. The concentration of the P-type host is preferably 10% or more.

[0049] As shown in FIG. 1(C), the guest molecules 105 are dispersed in the light-emitting layer 102. Not only that, but also the N-type host layer 103 and the P-type host layer 104 are dispersed in part. In the figure, G represents the concentration distribution of the guest.

[0050] In addition, in the N-type host layer 103, the concentration of the P-type host is extremely low, 0.1% or less. In the P-type host layer 104, the concentration of the N-type host is extremely low, 0.1% or less. Of course, the interface between the light-emitting layer 102 and the N-type host layer 103 and the light-emitting layer 10 The interface between the dopant 2 and the P-type host layer 104 does not necessarily have to have a steep concentration change.

[0051] FIG. 1(D) shows an example of another light-emitting element 101b of this embodiment. The light-emitting element 101b , a layer 103 of an N-type host, a layer 104 of a P-type host, and a light-emitting The light-emitting layer 102 has guest molecules 105 dispersed therein.

[0052] The difference from the light-emitting element 101a is that an N-type host is provided between the light-emitting layer 102 and the N-type host layer 103. The region where the concentration of the P-type host and the concentration of the P-type host change gradually (hereinafter referred to as the N-type transition region 106) and an N-type host layer is provided between the light-emitting layer 102 and the P-type host layer 104. The region where the concentration of the P-type host and the concentration of the P-type host change gradually (hereinafter referred to as the P-type transition region 107) ) is provided.

[0053] In addition, in the case of a structure that does not have either the N-type transition region 106 or the P-type transition region 107, In addition, the N-type transition region 106 and the P-type transition region 107 may have a light-emitting function. Therefore, the N-type transition region 106 and the P-type transition region 107 can also be considered as light-emitting layers in a broad sense. In that case, the light-emitting layer 102 may be considered the main light-emitting layer. The thickness of the P-type transition region 6 and the P-type transition region 107 is preferably 1 nm or more and 50 nm or less.

[0054] FIG. 1(E) shows the concentration distribution of the N-type host and the P-type host. In the P-type transition region 107, the concentration of the N-type host and the concentration of the P-type host change continuously. In addition, as shown in FIG. 1(F), the guest molecules 105 are not only present in the light-emitting layer 102 but also in the It may be included in the N-type transition region 106 or the P-type transition region 107, or further, in the N-type host. Alternatively, the layer 103 of the P-type host or the layer 104 of the P-type host may be provided so as to be included in the layer 103 of the P-type host or the layer 104 of the P-type host. The guest molecules 105 may be provided only in the light-emitting layer 102 .

[0055] FIG. 1G shows another light-emitting element 101c of this embodiment. In the light-emitting element 101c, As shown in FIG. 1(H), in the region sandwiched between the N-type host layer 103 and the P-type host layer 104, In this case, the concentration of the N-type host and the concentration of the P-type host are continuously changed. It is not possible to define the light-emitting layer (or the main light-emitting layer) in the light-emitting element 101a or the light-emitting element 101b. Although it is difficult, it is possible to use a mixture of N-type and P-type hosts. The region where the concentration of either of these elements is 10% or more can be called a light-emitting layer in a broad sense.

[0056] In addition, the concentration of the guest is set to a level that is included in the light-emitting layer in a broad sense, as shown in Figure 1(I). In FIG. 1, the P-type host layer 104 sandwiches the light-emitting layer 102. It is provided on the N-type host layer 103. However, this structure is convenient and the reverse is also possible. The structure in which the N-type host layer 103 is located above the P-type host layer 104, that is, the configuration, is also included in the form of the present invention. It can be easily understood that it is included in the form of the present invention.

[0057] The energy levels of the above light-emitting element 101a will be described using Fig. 2(A). As described above, For the HOMO levels and LUMO levels of the N-type host and P-type host, the HOMO level of the N-type host < the HOMO level of the P-type host < the LUMO level of the N-type host < the LUMO level of the P-type host. There is such a relationship.

[0058] On the other hand, in the light-emitting layer 102 in which the N-type host and P-type host are mixed, holes are transported using the HOMO level of the P-type host, and electrons are transported using the LUMO level of the N-type host. Therefore, from the perspective of carrier movement, the HOMO level can be regarded as the HOMO level of the P-type host, and the LUMO level can be regarded as the LUMO level of the N-type host. As a result, at the interface between the light-emitting layer 102 and the P-type host layer 104, a gap occurs in the LUMO level, which becomes a barrier for the movement of electrons. Similarly, at the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes. Since they are transported, from the perspective of carrier movement, the HOMO level can be regarded as the HOMO level of the P-type host, and the LUMO level can be regarded as the LUMO level of the N-type host. As a result, at the interface between the light-emitting layer 102 and the P-type host layer 104, a gap occurs in the LUMO level, which becomes a barrier for the movement of electrons. Similarly, at the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes. So, from the perspective of carrier movement, the HOMO level can be regarded as the HOMO level of the P-type host, and the LUMO level can be regarded as the LUMO level of the N-type host. As a result, at the interface between the light-emitting layer 102 and the P-type host layer 104, a gap occurs in the LUMO level, which becomes a barrier for the movement of electrons. Similarly, at the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes. And, as a result, at the interface between the light-emitting layer 102 and the P-type host layer 104, a gap occurs in the LUMO level, which becomes a barrier for the movement of electrons. Similarly, at the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes. Therefore, at the interface between the light-emitting layer 102 and the P-type host layer 104, a gap occurs in the LUMO level, which becomes a barrier for the movement of electrons. Similarly, at the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes. At the interface between the light-emitting layer 102 and the P-type host layer 104, a gap occurs in the LUMO level, which becomes a barrier for the movement of electrons. Similarly, at the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes. At the interface between the light-emitting layer 102 and the N-type host layer 103, a gap occurs in the HOMO level, which becomes a barrier for the movement of holes.

[0059] On the other hand, at the interface between the light-emitting layer 102 and the P-type host layer 104, the HOMO level is continuous. Therefore, there is no barrier for the movement of holes. Also, at the interface between the light-emitting layer 102 and the N-type host layer 103, the LUMO level is continuous. Therefore, there is no barrier for the movement of electrons.

[0060] As a result, electrons can easily move from the N-type host layer 103 to the light-emitting layer 102. However, due to the LUMO level gap between the light-emitting layer 102 and the P-type host layer 104, the light-emitting layer 10 2 The transfer from 2 to the P-type host layer 104 is hindered.

[0061] Similarly, holes can easily move from the P-type host layer 104 to the light-emitting layer 102, but due to the HOMO level gap between the light-emitting layer 1 02 and the N-type host layer 103, the transfer from the light-emitting layer 102 to the N-type host layer 103 is hindered. As a result, electrons and holes can be confined in the light-emitting layer 102.

[0062] Also, the energy levels of the above light-emitting element 101b will be described using FIG. 2(B). As described above, the HOMO levels and 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. 2(A), but attention needs to be paid to the N-type transition region 106 and the P-type transition region 107. In these regions, the concentration of the N-type host and the concentration of the P-type host change continuously.

[0063] However, unlike the case where the conduction band x In 1-x of an inorganic semiconductor material (e.g., Ga N(0 < x < 1)) and the valence band change continuously with the change in composition, the LUMO levels and HOMO levels of a mixed organic compound rarely change continuously. This is because the electrical conduction of an organic compound is a different method from that of an inorganic semiconductor, namely hopping conduction.

[0064] For example, when the concentration of the N-type host decreases and the concentration of the P-type host increases, it becomes difficult for electrons to conduct, not because the LUMO level continuously rises, but because the distance between N-type host molecules becomes longer, resulting in a decrease in the transfer probability, and because more energy is required for hopping to the high LUMO level of the neighboring P-type host. ​ do.

[0065] Therefore, in the N-type transition region 106, its HOMO is P The HOMO of the emissive layer 102 is a mixed state of the HOMO of the emissive layer 102. The probability of the HOMO of the N-type host is high, but as we approach the layer 103 of the N-type host, the probability of the HOMO of the N-type host increases. The same is true for the P-type transition region.

[0066] However, even if such an N-type transition region 106 and a P-type transition region 107 are present, the light emitting layer At the interface between the P-type host layer 102 and the P-type host layer 104, a gap occurs in the LUMO level. , which acts as a barrier to electron movement, and As shown in Figure 2( Same as A).

[0067] However, at an interface where the concentration changes sharply as in Figure 2(A), for example, electrons concentrate at the interface. There is a high probability that the particles will remain in the interface, which causes the area around the interface to deteriorate. However, in a state where the interface is ambiguous as in Figure 2(B), the location where the electrons stay is determined probabilistically. Therefore, no specific part will deteriorate. In other words, deterioration of the light emitting element is alleviated, and reliability is improved. can be increased.

[0068] On the other hand, the interface between the light emitting layer 102 and the P-type transition region 107, and the interface between the P-type transition region 107 and the P-type host At the interface of the layer 104, the HOMO level is continuous, so that the movement of holes is There is no barrier, and the interface between the light emitting layer 102 and the N-type transition region 106 and the N-type transition region 106 At the interface of the layer 103 of the fluorine-containing host, the LUMO level is continuous, and therefore, electrons move. There are no barriers.

[0069] As a result, electrons can easily move from the N-type host layer 103 to the light-emitting layer 102, but the P-type transition The LUMO level gap in the transition region 107 allows electrons to travel from the light-emitting layer 102 to the P-type host layer 104. Similarly, holes are prevented from moving from the P-type host layer 104 to the light-emitting layer 102. However, the gap in the HOMO level in the N-type transition region 106 allows the electrons in the light-emitting layer 1 Migration from O2 to the N-type host layer 103 is prevented.

[0070] As a result, electrons and holes can be confined in the light-emitting layer 102. The concentration of the N-type host between the layer 103 and the P-type host layer 104 is continuously In the light-emitting element 101c, which changes its polarity, electrons and holes are efficiently transferred to the N-type host by the same idea. It can be confined between layer 103 and layer 104 of a P-type host.

[0071] Next, the excitation process of the guest molecule 105 will be described. Here, the light-emitting element 101a will be taken as an example. The same applies to the light emitting element 101b and the light emitting element 101c. The excitation process includes a direct recombination process and an energy transfer process.

[0072] FIG. 2(C) is a diagram illustrating the direct recombination process, in which the layer 10 of the N-type host connected to the negative electrode Electrons are introduced from the P-type host layer 103 connected to the positive electrode, and holes are introduced from the P-type host layer 104 connected to the positive electrode. The guest molecule 105 is injected into the LUMO and HOMO of the light-emitting layer 102. Therefore, under appropriate conditions, electrons and positive charges are added to the LUMO and HOMO of the guest molecule. By injecting holes, guest molecules can be excited (intramolecular excitons). Cut.

[0073] However, the guest molecules sparsely present in the light-emitting layer 102 have electrons in the LUMO and HOMO. Since it is technically difficult to efficiently inject electrons and holes, the probability of this process is sufficiently high. For higher efficiency, the LUMO of the guest should be 0.1 V higher than the LUMO of the N-type host. By lowering the temperature by 0.5 to 0.3 electron volts, electrons are preferentially tracked to guest molecules. It is advisable to align the HOMO of the guest by 0.1 eV or more above the HOMO of the p-type host. The same effect can be obtained by increasing the voltage by 0.3 eV. The MO of the guest is lower than the HOMO of the P-type host, but the LUMO of the guest is higher than that of the N-type host and the P-type host. Since the LUMO is sufficiently lower than that of the LUMO of the

[0074] The LUMO of the guest is at least 0.5 eV lower than the LUMO of the N-type host (or makes the guest HOMO more than 0.5 eV higher than the p-type host HOMO) and Although the probability of trapping electrons (holes) increases, the conductivity of the light-emitting layer 102 decreases. This is not desirable because only the guest molecules on the positive electrode side are excited intensively.

[0075] FIG. 2(D) shows the structure of the excimer laser by appropriately selecting the N-type host and the P-type host according to the present invention. 1 is a diagram illustrating the case where electrons and holes are formed in the light-emitting layer 102 in the same manner as described above. When the guest molecule is injected, the electron and hole are more likely to meet at the adjacent emitting layer 102 than at the guest molecule. In such cases, the probability of an encounter between an N-type host molecule and a P-type host molecule is higher. , forming an exciplex. Here, the exciplex will be explained in detail.

[0076] Exciplexes are formed by interactions between different molecules in an excited state. The complex consists of an organic compound (N-type host) with a relatively deep LUMO level and a HO It is generally known that it is easy to form between organic compounds (p-type hosts) that have MO levels. There are.

[0077] The emission wavelength from the exciplex depends on the HOMO and LUMO levels of the N-type and P-type hosts. It depends on the energy difference between the levels. If the energy difference is large, the emission wavelength becomes shorter, and The smaller the energy difference, the longer the emission wavelength. When an exciplex is formed, the LUMO level of the exciplex is higher than that of the N-type host. The HOMO level comes from the P-type host.

[0078] Therefore, the energy difference of the exciplex is the energy difference of the N-type host and the P-type The energy difference between the N-type and P-type hosts is smaller than that between the N-type and P-type hosts. The emission wavelength of the exciplex is longer than that of the luminescent wavelength.

[0079] The exciplex formation process can be broadly divided into two processes.

[0080] ≪Electroplex≫ As used herein, an electroplex is a compound having an N-type host in the ground state and a P-type host in the ground state. This refers to an exciplex formed directly from an N-type host. For example, The exciplex formed directly from the cation of the cation and the p-type host is electroplexed. It's a kus.

[0081] As mentioned above, in the energy transfer process of the conventional light-emitting process of organic compounds, electrons and The hole and the host molecule are recombined (excited), and the excited state of the host molecule transfers the excited state to the guest molecule. The photoelectron energy is transferred, and the guest molecule reaches an excited state, emitting light.

[0082] Here, before the excitation energy is transferred from the host molecule to the guest molecule, the host molecule itself When light is emitted or the excitation energy is converted into thermal energy, the excitation energy is deactivated. In addition, when the host molecule is in the singlet excited state, the excited state is higher than when it is in the triplet excited state. The excitation energy is easily lost due to the short lifetime. This is one of the factors that leads to deterioration and reduced lifespan of the child.

[0083] However, when the N-type host molecule and the P-type host molecule are in a state with carriers (cation or aniline), If electroplexes are formed from the ionized state, the formation of singlet excitons with short excitation lifetimes can be suppressed. In other words, exciplexes can be directly formed without forming singlet excitons. This allows the formation of one of the N-type host molecules or the P-type host molecule. It is also possible to suppress the deactivation of the doublet excitation energy. It can be realized.

[0084] In this way, the generation of the singlet excited state of the host molecule is suppressed, and instead the generated electron Energy transfer from the tropoplex to the guest molecule creates a light-emitting device with high luminous efficiency. The concept of obtaining this is unprecedented.

[0085] <Exciplex formation by excitons> Another process is when one of the N-type and P-type host molecules forms a singlet exciton. After the formation of the exciplex, the elementary process of the exciplex can be considered. Unlike electroplexing, in this case, the N-type host molecule or the P-type host molecule is first Although a singlet excited state of the ion-excited molecule is generated, it is quickly converted to an exciplex. Therefore, the deactivation of the singlet excitation energy can be suppressed. The molecules can be prevented from losing their excitation energy.

[0086] In addition, when the difference between the HOMO level and the LUMO level of the N-type host and the P-type host is large, (Specifically, the difference is 0.3 eV or more), electrons preferentially enter the N-type host molecule, and holes preferentially enter the N-type host molecule. In this case, exciplexes are formed via singlet excitons. The process of electroplex formation seems to be prioritized over the process of ionization. .

[0087] In order to increase the efficiency of the energy transfer process, the importance of absorption due to the MLCT transition must be emphasized. Considering this, in both the Förster mechanism and the Dexter mechanism, the N-type host (or P-type host) alone (or the corresponding energy difference) and Rather than overlapping with the absorption spectrum of the It is advantageous to increase the overlap between the emission spectrum of the exon and the absorption spectrum of the guest. .

[0088] In order to increase the energy transfer efficiency, the guest concentration should be small enough that concentration quenching is not a problem. It is preferable to increase the concentration, and the concentration of the guest relative to the total amount of the N-type host and the P-type host is The weight ratio is preferably 1% to 9%.

[0089] In addition, both the direct excitation recombination process and the energy transfer process described above are The guest molecules present in the host are exciplexes of the N-type host and the P-type host, and The concept of generating an excited state by energy transfer from an electron or an electronplex has not been known. This concept is referred to as Guest Coupled with Comp By using this concept, In this embodiment, carrier confinement and reduction of the carrier injection barrier to the light-emitting layer are achieved simultaneously. Not only is this achieved, but it also forms an exciplex with the host molecule, resulting in a singlet excited state. Since the energy transfer process from both triplet excited states can be utilized, Furthermore, a light-emitting element that can be driven at a low voltage (that is, has very high power efficiency) can be obtained.

[0090] (Embodiment 2) An example of the light-emitting device of this embodiment is shown in FIG. The light emitting element 101 described in the first embodiment (the light emitting element 101a described in the first embodiment, the light emitting element The light-emitting element 101b, the light-emitting element 101c, etc. are sandwiched between a negative electrode 108 and a positive electrode 109. It is preferable that at least one of the negative electrode 108 and the positive electrode 109 is transparent. The device may be provided on a suitable substrate.

[0091] In the light-emitting element 101, a light-emitting layer 102 is sandwiched between an N-type host layer 103 and a P-type host layer 104. Layer 104 functions as an electron transport layer and a hole transport layer, respectively, and as described above, Since it has the function of blocking holes and electrons, layers equivalent to the electron transport layer and hole transport layer are separately provided. Therefore, the manufacturing process of the light-emitting device shown in FIG.

[0092] The light-emitting device 101 is made of a guest, an N-type host, and a P-type host, as described in the first embodiment. The N-type host (or P-type host) can be composed of two or more substances.

[0093] As the guest, an organometallic complex is preferred, and an iridium complex is particularly preferred. Considering the energy transfer by the Förster mechanism, the longest wavelength side of the phosphorescent compound The molar extinction coefficient of the absorption band located is 2000M -1 ·cm -1 More than 5000 is preferable. M -1 ·cm -1 The above is particularly preferred.

[0094] An example of a compound having such a large molar absorption coefficient is bis(3,5-dimethyl Iridium(III) (2-phenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(mppr-Me)2(dpm)] (see Chemical Formula 1 below) and (acetylacetone Iridium(III) (abbreviation: [Ir (dppm)2(acac)], see the following chemical formula (see Chemical Formula 2), etc. r(dppm)2(acac)], with a molar extinction coefficient of 5000M -1 ·cm -1 Below By using materials that reach the above level, it is possible to obtain a light-emitting device with an external quantum efficiency of approximately 30%.

[0095] [ka]

[0096] [ka]

[0097] Examples of N-type hosts include compounds having a π-electron deficient heteroaromatic ring. Contains heteroatoms (such as nitrogen and phosphorus) that are more electronegative than carbon as ring constituent elements Examples of compounds that have a six-membered aromatic ring include 2-[3-(dibenzothiophene)-2-(dibenzothiophene)]. phen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPD Bq-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]di Benzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II) and 6-[3-( Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6 mDBTPDBq-II) which has a benzoquinoxaline skeleton that readily accepts electrons Any one of the compounds (benzoquinoxaline derivatives) may be used.

[0098] As a p-type host, aromatic amines (a compound having at least one aromatic ring bonded to a nitrogen atom) are used. compounds) and carbazole derivatives. For example, 4,4'-di(1-naphthyl)- 4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl Nyl (abbreviated as NPB or α-NPD) and 4-phenyl-4'-(9-phenyl- 9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP) Any compound that easily accepts holes may be used. However, the present invention is not limited to these compounds, and P Any combination of a N-type host and an N-type host may be used as long as they can form an exciplex.

[0099] The positive electrode 109 is made of a metal, alloy, or conductor having a large work function (specifically, 4.0 eV or more). It is preferable to use conductive compounds and mixtures thereof. Indium tin oxide (ITO), silicon or oxide Silicon-containing indium oxide-tin oxide, indium oxide-zinc oxide, tungsten oxide Examples include indium oxide containing zinc oxide (IWZO). Metal oxide films are usually formed by sputtering, but they can also be formed by applying the sol-gel method. It is also acceptable to make it in this way.

[0100] For example, an indium oxide-zinc oxide film is made of indium oxide with 1 to 20 wt% zinc oxide. It can be formed by sputtering using a target containing lead. The WZO film is made of indium oxide with 0.5 to 5 wt% tungsten oxide and 0.0 wt% zinc oxide. It can be formed by sputtering using a target containing 0.1 to 1 wt% of Other materials include graphene, gold, platinum, nickel, tungsten, chromium, molybdenum, and iron. , cobalt, copper, palladium, or nitrides of metal materials (for example, titanium nitride), etc. can be.

[0101] However, in the light emitting element 101, the layer formed in contact with the positive electrode is made of an organic compound and an electron When a composite material containing a cathode and an acceptor is used, The materials used include various metals, alloys, electrically conductive compounds, and For example, aluminum, silver, aluminum alloys, and mixtures thereof can be used. An alloy containing Al (for example, Al-Si) can also be used. The film can be formed by coating, vapor deposition (including vacuum deposition), or the like.

[0102] The negative electrode 108 is made of a metal, alloy, or electrically conductive material having a small work function (preferably 3.8 eV or less). It is preferable to form the layer using a compound containing an element, a compound containing an element, a mixture of these elements, or the like. Elements in Groups 1 or 2 of the periodic table, i.e., alkali metals such as lithium and cesium metals, and alkaline earth metals such as calcium and strontium, magnesium, and Alloys containing these elements (e.g., Mg-Ag, Al-Li), europium, ytterbium, etc. The rare earth metals and alloys containing these can be used.

[0103] However, in the light emitting element 101, the layer formed in contact with the negative electrode is made of an organic compound and an electron When using a composite material that is mixed with a donor, regardless of the magnitude of the work function, In addition, Al, Ag, ITO, silicon or silicon oxide-containing indium oxide-tin oxide, etc. Various conductive materials can be used. When forming the negative electrode, a vacuum deposition method or Sputtering can be used. When silver paste or the like is used, the coating For example, a printing method or an ink jet method can be used.

[0104] An example of the light-emitting device of this embodiment is shown in FIG. In the light-emitting device shown in (A), an electron injection layer 113 is disposed between the light-emitting element 101 and the negative electrode 108. In addition, a hole injection layer 114 is provided between the light emitting element 101 and the positive electrode 109 .

[0105] By providing the electron injection layer 113 and the hole injection layer 114, the emission from the negative electrode 108 and the positive electrode 109 Electrons and holes can be efficiently injected into the optical element 101, improving the energy utilization efficiency. The laminated body having the light emitting element 101, the electron injection layer 113, and the hole injection layer 114 is formed as an EL layer 11. It's called 0.

[0106] The hole injection layer 114 is a layer containing a substance with high hole injection properties. The oxides are molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, Aluminum oxide, Chromium oxide, Zirconium oxide, Hafnium oxide, Tantalum oxide, Silver Metal oxides such as oxides of tungsten, manganese, etc. can be used. Phthalocyanine (abbreviation: HPc), copper(II) phthalocyanine (abbreviation: CuPc) Phthalocyanine compounds such as the above can be used.

[0107] In addition, the low molecular weight organic compound 4,4',4''-tris(N,N-diphenylamino) ) triphenylamine (abbreviation: TDATA), 4,4',4''-tris[N-(3-methylphenyl) (N-phenylamino)triphenylamine (abbreviation: MTDATA), 4 ,4'-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl DPAB, 4,4'-bis(N-{4-[N'-(3-methylphenyl)- N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated as DNTP D), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino] 3-[N-(9-phenylcarbazol-3-yl)benzene (abbreviation: DPA3B) )-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3, 6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9- Phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-( 9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: P Aromatic amine compounds such as CzPCN1) can be used.

[0108] Furthermore, polymer compounds (including oligomers and dendrimers) can also be used. For example, poly(N-vinylcarbazole) (abbreviated as PVK), poly(4-vinyltriphenyl amine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamine N-phenyl-N'-phenylamino-phenyl methacrylamide :PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl) Examples of polymer compounds include poly(phenyl)benzidine (abbreviation: Poly-TPD). Poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PE DOT / PSS), polyaniline / poly(styrene sulfonate) (PAni / PSS), etc. A polymer compound to which an acid such as the above has been added can be used.

[0109] The hole injection layer 114 is formed by mixing an organic compound and an electron acceptor. Such composite materials may be used in which the electron acceptor is attached to the organic compound. Since holes are generated, the organic compound has excellent hole injection and hole transport properties. The material is preferably a material that is excellent in transporting generated holes (a material with high hole transport properties). It's nice.

[0110] The organic compounds used in the composite materials include aromatic amine compounds, carbazole derivatives, aromatic Uses various compounds such as aromatic hydrocarbons, polymers (including oligomers and dendrimers) As the organic compound used for the composite material, an organic compound having a high hole transporting property can be used. It is preferable that the material is a material having a molecular weight of 1000 or more. -6 cm 2 / Vs or higher hole mobility However, as long as the material has a higher hole transporting property than the electron transporting property, these In the following, specific examples of organic compounds that can be used in the composite material are listed. List them specifically.

[0111] Examples of organic compounds that can be used in composite materials include TDATA and MTDATA. , DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN 1,1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P- II), 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation N,N'-bis(3-methylphenyl)-N,N'-diphenyl ether (NPB or α-NPD) Phenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4-phenyl Nyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPA Aromatic amine compounds such as FLP and 4,4'-di(N-carbazolyl)biphenyl (abbreviation CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation Name: TCPB), 9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene CzPA, 9-phenyl-3-[4-(10-phenyl-9-anthryl) )phenyl]-9H-carbazole (abbreviation: PCzPA), 1,4-bis[4-(N-carbazole) Carbazole derivatives such as [(carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene A conductor may be used.

[0112] In addition, 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t- BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9 ,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-t ert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: tB uDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10- Diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene ( Abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA), 9,10-bis[2-(1-naphthyl)phenyl]-2-tert -butylanthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene , 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, and other aromatic compounds Aromatic hydrocarbon compounds can be used.

[0113] Furthermore, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthryl, 10,10'-diphenyl-9,9'-bianthryl, 10, 10'-bis(2-phenylphenyl)-9,9'-bianthryl, 10,10'-bis [(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthryl, Thracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-buthylene) (ethyl)perylene, pentacene, coronene, 4,4'-bis(2,2-diphenylvinyl) Biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl) Aromatic hydrocarbon compounds such as diphenylanthracene (abbreviation: DPVPA) can be used. can.

[0114] The electron acceptor is 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroethylene. Organic compounds such as fluoroquinodimethane (abbreviated as F4-TCNQ), chloranil, and Examples of oxides of transition metals include those belonging to Groups 4 to 8 of the above-mentioned oxides. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, Tungsten oxide, manganese oxide, and rhenium oxide are preferred because of their high electron-accepting properties. In particular, molybdenum oxide is preferred because it is stable in the air, has low hygroscopicity, and is easy to handle. stomach.

[0115] In addition, the above-mentioned polymers such as PVK, PVTPA, PTPDMA, Poly-TPD, etc. The above-mentioned electron acceptors may be used to form a composite material for the hole injection layer 114 .

[0116] The electron injection layer 113 is a layer containing a substance with high electron injection properties. lithium, cesium, calcium, lithium fluoride, cesium fluoride, calcium fluoride, Alkali metals, alkaline earth metals, or compounds thereof, such as lithium oxide, are used. Also, rare earth metal compounds such as erbium fluoride can be used. Cut.

[0117] Alternatively, a substance with a high electron-transporting property can be used for the electron-injecting layer 113. Highly effective materials include Alq3, tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3), bis(10-hydroxybenzo[h]quinolinato)beryllium ( Abbreviation: BeBq2), BAlq, Zn(BOX)2, bis[2-(2-hydroxyphenyl) Examples of metal complexes include [benzothiazolato]zinc (abbreviated as Zn(BTZ)2).

[0118] Also, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4 -Oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl) Nyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3 -(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1, 2,4-Triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4- (4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation :p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine ( Abbreviation: BCP), 4,4'-bis(5-methylbenzoxazol-2-yl)stilbe Heteroaromatic compounds such as benzophenone (abbreviation: BzOs) can also be used.

[0119] In addition, poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexyl) PF -Py), poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2 PF-BPy) The materials mentioned here are mainly 10 -6 cm 2 / Vs or higher electron mobility It is a substance that

[0120] Note that any substance other than those mentioned above can be used as long as it has a higher electron transporting property than hole transporting property. These substances having high electron transport properties may also be used in the electron transport layer described later. It is possible.

[0121] Alternatively, the electron injection layer 113 may be formed of a composite material made by mixing an organic compound and an electron donor (donor). Such composite materials are formed by adding electrons to an organic compound via an electron donor. In this case, the organic compound It is preferable that the material is excellent in transporting the generated electrons. Specifically, for example, The material constituting the electron transport layer (metal complex, heteroaromatic compound, etc.) can also be used.

[0122] The electron donor may be any substance that exhibits electron donating properties to organic compounds. Alkali metals, alkaline earth metals and rare earth metals are preferred, and lithium, cesium, magnesium Examples include nesium, calcium, erbium, and ytterbium. Metal oxides and alkaline earth metal oxides are preferred, and lithium oxide, calcium oxide, barium oxide, etc. Also, Lewis bases such as magnesium oxide can be used. It is also possible to use organic compounds such as tetrathiafulvalene (TTF). can.

[0123] An example of the light-emitting device of this embodiment is shown in FIG. In the light-emitting device shown in (B), an electron transport layer 11 is provided between the light-emitting element 101 and the electron injection layer 113. 1, and a hole transport layer 112 is provided between the light emitting element 101 and the hole injection layer 114. be.

[0124] As described above, the N-type host layer 103 and the P-type host layer 104 in the light-emitting device 101 are , which also function as an electron transport layer and a hole transport layer, respectively, in the light-emitting element 101. To inject electrons and holes more effectively, an electron transport layer 111 and a hole transport layer 112 are separately formed. It is a good idea to set one up.

[0125] The electron transport layer 111 is a layer containing a substance with a high electron transport property. The electron transport layer can be a single layer. In addition, two or more layers made of the above materials may be laminated.

[0126] The hole-transporting layer 112 is a layer containing a substance with a high hole-transporting property. NPB, TPD, BPAFLP, 4,4'-bis[N-(9,9-dimethylfluoromethyl] 4,4-Diphenyl-2-yl)-N-phenylamino]biphenyl (abbreviation: DFLDPBi), '-Bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino] Aromatic amine compounds such as biphenyl (abbreviation: BSPB) can be used. The substances mentioned are mainly 10 -6 cm 2 / Vs or more. Any substance other than these may be used as long as it has a higher hole transporting property than an electron transporting property. The layer containing a substance with a high hole transporting property may be a single layer or may be two or more layers containing the above substance. It may also be laminated on top.

[0127] The hole transport layer 112 may also contain carbazole derivatives such as CBP, CzPA, and PCzPA. Anthracene derivatives such as t-BuDNA, DNA, and DPAnth may also be used. The hole transport layer 112 may contain PVK, PVTPA, PTPDMA, Poly-TP Polymer compounds such as D can also be used.

[0128] The hole injection layer 114, the hole transport layer 112, the light emitting element 101, the electron transport layer 111, and the electron The electron injection layer 113 can be formed by a method such as vapor deposition (including vacuum deposition), ink jetting, or coating. It is not necessary for the EL layer 110 to have all of these layers. stomach.

[0129] As shown in FIG. 3D, a plurality of EL layers 110a are disposed between the positive electrode 109 and the negative electrode 108. In this case, the EL layers 110a and 110b may each be a small At least the light emitting element 101 shown in FIG. 3(A) or the light emitting element 101 shown in FIG. 3(B) and FIG. 3(C) Between the stacked EL layer 110a and the EL layer 110b, a charge generation layer The charge generation layer 115 is formed from the above-mentioned material or composite material with high hole injection properties. The charge generating layer 115 may be a layer made of a composite material and a layer made of another material. A laminated structure may also be used.

[0130] In this case, the layer made of another material may include a material having an electron donating property and a material having a high electron transporting property. A layer made of a transparent conductive film or a layer made of a phosphorescent film can be used. On the other hand, fluorescent light may be obtained. This phosphorescent light can be obtained by using the above-mentioned EL layer structure. can be done.

[0131] Furthermore, by making the luminescent color of each EL layer different, the light emitting device as a whole can be made to have a desired color. For example, the luminescence color of the EL layer 110a and the luminescence color of the EL layer 110b can be obtained. To obtain a light emitting device that emits white light as a whole by making the light colors have a complementary color relationship. The same is true for a light-emitting device having three or more EL layers.

[0132] Alternatively, as shown in FIG. 3(E), a hole injection layer 11 is formed between the positive electrode 109 and the negative electrode 108. 4, hole transport layer 112, light emitting element 101, electron transport layer 111, electron injection buffer layer 11 6, an EL layer 11 having an electron relay layer 117 and a composite material layer 118 in contact with the negative electrode 108; 0 may be formed.

[0133] By providing the composite material layer 118 in contact with the negative electrode 108, it is possible to form a negative electrode 108 by using a sputtering method in particular. When forming the electrode 108, damage to the EL layer 110 can be reduced. The composite material layer 118 is preferably formed by adding an acceptor to the organic compound having a high hole transporting property. A composite material containing a reactive substance can be used.

[0134] Furthermore, by providing an electron injection buffer layer 116, the composite material layer 118 and the electron transport layer 119 are Since the injection barrier between the composite material layer 118 and the electrode 11 can be reduced, the electrons generated in the composite material layer 118 can be injected into the electrode 11. The electrons can be easily injected into the electron transport layer 111.

[0135] The electron injection buffer layer 116 contains an alkali metal, an alkaline earth metal, a rare earth metal, and and their compounds (alkali metal compounds (oxides such as lithium oxide, halides, carbonates) Alkaline earth metal compounds (including carbonates such as lithium and cesium carbonate), oxides, halides compounds of rare earth metals (including oxides, halides, carbonates) or rare earth metal compounds (including oxides, halides, carbonates) It is possible to use a substance with high electron injection properties, such as tetrahydrofuran (Tetrahydrofuran) and tetrahydrofuran (Tetrahydrofuran).

[0136] The electron injection buffer layer 116 is formed by containing a substance with high electron transporting properties and a donor substance. When the compound is formed, the mass ratio to the substance having high electron transport properties is 0.001 or more and 0.1 or less It is preferable to add a donor substance in a ratio of The electron transport layer 111 can be formed using the same material as that of the electron transport layer 111 described above.

[0137] In addition, the donor substance may be an alkali metal, an alkaline earth metal, a rare earth metal, or the like. These compounds (alkali metal compounds (oxides such as lithium oxide, halides, lithium carbonate, etc.) Alkaline earth metal compounds (including oxides, halides, etc.), compounds of rare earth metals (including oxides, halides, carbonates) or compounds of rare earth metals (including oxides, halides, carbonates) )), as well as tetrathianaphthacene (abbreviation: TTN), nickelocene, decamethylnickelocene, Organic compounds such as benzene can also be used.

[0138] Furthermore, an 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, but it is preferable to form the electron relay layer 117. By providing the electron relay layer 117 with high transportability, electrons can be transferred to the electron injection buffer layer 116. It will be possible to send it quickly.

[0139] The electron relay layer 117 is sandwiched between the composite material layer 118 and the electron injection buffer layer 116. The structure is composed of an acceptor material contained in the composite material layer 118 and an electron injection buffer layer 11 The structure is such that it is less likely to interact with the donor substance contained in 6 and to inhibit each other's functions. Therefore, an increase in the driving voltage can be prevented.

[0140] The electron relay layer 117 contains a substance with high electron transport properties, and the LUMO of the substance with high electron transport properties The level is the LUMO level of the acceptor material contained in the composite material layer 118 and the LUMO level of the electron transport layer The layer is formed so as to be between the LUMO level of the highly electron transporting substance contained in 111 and the LUMO level of the highly electron transporting substance contained in 111.

[0141] In addition, when the electron relay layer 117 contains a donor material, the donor phase of the donor material The LUMO level of the acceptor material in the composite material layer 118 and the LUMO level of the electron transport layer 111 The LUMO level of the material with high electron transport properties is set to be between the specific energy The energy level of the material with high electron transport properties contained in the electron relay layer 117 is The MO level is set to -5.0 eV or more, preferably -5.0 eV or more and -3.0 eV or less. stomach.

[0142] The electron relay layer 117 contains a material with high electron transport properties, such as a phthalocyanine-based material. It is preferable to use a metal complex having a metal-oxygen bond and an aromatic ligand.

[0143] The phthalocyanine-based material contained in the electron relay layer 117 is specifically CuPc, S nPc (Phthalocyanine tin(II) complex), ZnPc (Phthalocyanine zinc complex), CoPc (Cobal t(II)phthalocyanine, β-form), FePc(Phthal ocyanine Iron) and PhO-VOPc(Vanadyl 2,9,16, 23-tetraphenoxy-29H,31H-phthalocyanine) It is preferable to use either one.

[0144] The metal complexes having a metal-oxygen bond and an aromatic ligand contained in the electron relay layer 117 include: It is preferable to use a metal complex having a metal-oxygen double bond. In this case, the molecule has acceptor properties (the ability to easily accept electrons), which facilitates electron transfer (donation and receipt). In addition, metal complexes with metal-oxygen double bonds are thought to be stable. Therefore, the use of a metal complex having a metal-oxygen double bond can improve the life of a light-emitting device. It can improve lives.

[0145] As a metal complex having a metal-oxygen bond and an aromatic ligand, a phthalocyanine-based material is preferred. Specifically, VOPc (Vanadyl phthalocyanine), SnO Pc(Phthalocyanine tin(IV) oxide complex) and TiOPc (Phthalocyanine titanium oxide co complex) are preferred because of their high acceptor properties.

[0146] The above-mentioned phthalocyanine-based material preferably has a phenoxy group. Specifically, a phthalocyanine derivative having a phenoxy group, such as PhO-VOPc, is preferred. Phthalocyanine derivatives having a phenoxy group are easily soluble in solvents and are therefore easy to handle. This has the advantage that the maintenance of the film forming apparatus is easy.

[0147] The electron relay layer 117 may further contain a donor material. Alkali metals, alkaline earth metals, rare earth metals and their compounds (alkali metal compounds) (Oxides such as lithium oxide, halides, carbonates such as lithium carbonate and cesium carbonate (including oxides, halides, and carbonates), or rare earth metal compounds Compounds of metals (including oxides, halides, and carbonates), as well as tetrathianaphthacene (abbreviation: TTN), nickelocene, decamethylnickelocene, and other organic compounds are used. By including these donor substances in the electron relay layer 117, the electron This facilitates mobility and allows the light-emitting device to be driven at a lower voltage.

[0148] When the electron-relay layer 117 contains a donor substance, the above-mentioned In addition to the material, the acceptor level of the acceptor substance contained in the composite material layer 118 A substance with a high LUMO level can be used. Specific energy levels are: , and the LUMO level is in the range of -5.0 eV or more, preferably in the range of -5.0 eV or more and -3.0 eV or less. It is preferable to use a substance having a structure such as a perylene derivative. Nitrogen-containing condensed aromatic compounds are examples of such compounds. Therefore, it is a preferable material to be used for forming the electron relay layer 117. do.

[0149] Specific examples of perylene derivatives include 3,4,9,10-perylenetetracarboxylic dianhydride. (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxylic bisbenzyl Zoimidazole (abbreviation: PTCBI), N,N'-dioctyl-3,4,9,10-periodic Phenylenetetracarboxylic diimide (abbreviation: PTCDI-CH), N,N'-dihexyl- 3,4,9,10-perylenetetracarboxylic diimide (abbreviation: Hex PTC) It can be obtained.

[0150] Specific examples of nitrogen-containing condensed aromatic compounds include pyrazino[2,3-f][1,10] Phenanthroline-2,3-dicarbonitrile (PPDN), 2,3,6,7,1 0,11-Hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation :HAT(CN)6), 2,3-diphenylpyrido[2,3-b]pyrazine (abbreviation: 2P YPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (abbreviation :F2PYPR) etc.

[0151] Other examples include 7,7,8,8-tetracyanoquinodimethane (TCNQ), 1,4, 5,8-Naphthalenetetracarboxylic dianhydride (abbreviation: NTCDA), Perfluorinated phthalocyanine, copper hexadecafluorophthalocyanine (abbreviation: F 16 CuPc), N,N'-bi S(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoro (N-octyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (abbreviation: NTCD I-C8F), 3',4'-dibutyl-5,5''-bis(dicyanomethylene)-5,5 ''-Dihydro-2,2':5',2''-terthiophene) (abbreviation: DCMT), meta fullerenes (e.g., [6,6]-phenyl C 61Butyric acid methyl ester) This can be done.

[0152] When the electron-relay layer 117 contains a donor substance, the donor substance is a substance with high electron transporting properties. The electron relay layer 117 may be formed by a method such as co-evaporation with an insulating material.

[0153] As described above, the layer 103 of the N-type host and the layer 104 of the P-type host in the light emitting device 101 The layers 104 also function as an electron transport layer and a hole transport layer, respectively. Either or both of the transport layer 111 and the hole transport layer 112 may be omitted. The N-type host layer 103 functions as an electron transport layer 111 .

[0154] In the light-emitting device described above, a current flows due to a potential difference between the positive electrode and the negative electrode, and the EL layer 1 Light is emitted by recombination of holes and electrons in 10 (or 110a, 110b). This light is then taken out through either the positive or negative electrode or both. Therefore, either the positive electrode or the negative electrode, or both, are transparent to visible light. The electrode has excellent properties.

[0155] A hole blocking layer may be combined with the light emitting element 101 .

[0156] The light-emitting device shown in this embodiment mode can be used to produce a passive matrix light-emitting device or a transistor light-emitting device. An active matrix light-emitting device is manufactured in which the driving of the light-emitting device is controlled by a photodiode. The light-emitting device can be applied to electronic devices, lighting devices, and the like.

[0157] (Embodiment 3) In this embodiment, the device for manufacturing the light emitting element 101a etc. described in the first embodiment is The manufacturing method will be described. The manufacturing apparatus shown in FIG. 4(A) has the following components in a vacuum chamber 201: The first evaporation source 202, the second evaporation source 203, and the third evaporation source 204 are included. Each of the evaporation sources 202 to 204 has a linear opening 223 as shown in FIG. 4(C). The organic compounds inside can be evaporated using a resistance heating method.

[0158] Here, the first evaporation source 202 evaporates an N-type host, and the second evaporation source 203 evaporates a guest. The first evaporation source 203 evaporates a P-type host, and the third evaporation source 204 evaporates a P-type host. The three evaporation sources 202 to 204 may each be provided with a shutter. It is advisable to control the temperature independently so that the vapor pressure of the organic compound can be appropriately controlled. For example, the evaporation amount of the N-type host is set to four times that of the P-type host, and the evaporation amount of the guest is set to P It may be set to 1% of the evaporation amount of the mold host.

[0159] Furthermore, for example, the first evaporation source 202 and the third evaporation source 204 can be used to relatively widely disperse organic compounds. In contrast, the second evaporation source 203 scatters the vapor in a narrower range. In this way, the shape and size of the openings 223 of the evaporation sources may be made different. As shown in FIG. 4(A), the openings 223 of the evaporation sources may be set to face in different directions.

[0160] In addition, one or more substrates, preferably two or more substrates (FIG. 2( In A), the substrates 205-207 are placed, and the evaporation source is opened from left to right as shown in the figure. It is advisable to move the nozzle 223 at an appropriate speed in a direction substantially perpendicular to the direction of the nozzle 223. The distance between the evaporation source and the substrates 205 to 207 may be varied.

[0161] In the manufacturing apparatus shown in FIG. 4(A), the portion indicated by 208 mainly includes the first evaporation source 20 The N-type host scattered from the first evaporation source 202 is deposited. the N-type host scattered from the second evaporation source 203, the guest scattered from the third evaporation source 204, The P-type host scattered from the surface is deposited at a certain rate. Then, the P-type host scattered from the third evaporation source 204 is deposited.

[0162] Therefore, while the substrates 205-207 are moving from left to right, the layer 10 of the N-type host is first 3 is formed, then the light-emitting layer 102 is formed, and then the P-type host layer 104 is formed. As in the light-emitting device 101b, an N-type transition metal is formed between the N-type host layer 103 and the light-emitting layer 102. A P-type transition region 107 is formed between the P-type host layer 104 and the light-emitting layer 102. Alternatively, as in the light-emitting element 101c, the light-emitting layer and the N-type host layer 103 may be In some cases, a clear boundary may not be formed between the light-emitting layer and the P-type host layer 104. .

[0163] The manufacturing apparatus shown in FIG. 4(B) is an improved version of the manufacturing apparatus shown in FIG. 4(A). That is, a first evaporation source 212, a second evaporation source 213, a third evaporation source 214, and a third evaporation source 215 are disposed in a vacuum chamber 211. The first evaporation source 214, the fourth evaporation source 215, and the fifth evaporation source 216 are included. The second evaporation source 212 and the second evaporation source 213 evaporate the N-type host, and the third evaporation source 214 evaporates the guest. The fourth evaporation source 215 and the fifth evaporation source 216 evaporate a P-type host. Let's say.

[0164] As with the manufacturing apparatus shown in FIG. 4(A), the shape and size of the opening 223 of each vapor deposition source, The positions and orientations of the substrates may be different from each other. Preferably, two or more substrates (substrates 217 to 219 in FIG. 2(B)) are arranged. It is best to move from left to right at an appropriate speed.

[0165] In the manufacturing apparatus shown in FIG. 4(B), the portion indicated by 220 mainly includes the first evaporation source 21 The N-type host scattered from the second evaporation source 213 is deposited in the area indicated by 221. the N-type host scattered from the third evaporation source 214, the guest scattered from the fourth evaporation source 215, The P-type host scattered from the surface is deposited at a certain rate. Then, the P-type host scattered from the fifth evaporation source 216 is deposited.

[0166] In the manufacturing apparatus shown in FIG. 4(B), a light-emitting layer 102 and an N-type host are formed as in the light-emitting element 101a. The concentration change at the interface with the layer 103 and the interface between the light-emitting layer 102 and the P-type host layer 104 is It can be made steeper.

[0167] (Fourth embodiment) In this embodiment, 2mDBTPDBq-II and P PCBNBB, which can be used as a mold host, and its exciplex are explained. 2mDBTPDBq-II, PCBNBB, and the guest [Ir(dppm)2(acac)], [Ir(mppr-Me)2(dpm) The main physical properties of ] are as shown in Table 1.

[0168] [Table 1]

[0169] In the mixed region of 2mDBTPDBq-II and PCBNBB, the LUMO level is -2 The HOMO level is -5.46 eV and the 2mDBTP level is -0.78 eV. The LUMO and HOMO levels of the exciplex of DBq-II and PCBNBB are the same. And the LUMO level of the guest [Ir(mppr-Me)2(dpm)] is The HOMO level is also at the same level.

[0170] On the other hand, the LUMO and HOMO levels of [Ir(dppm)2(acac)] are both Since the charge transport potential is lower than that of [Ir(dppm)2(acac)], it is easy to trap electrons. Therefore, when [Ir(dppm)2(acac)] is used as the guest, [ The probability of direct recombination is higher than that of the case using [Ir(mppr-Me)2(dpm)]. This suggests that...

[0171] Also, [Ir(mppr-Me)2(dpm)] is also [Ir(dppm)2(acac)] The triplet excited state energy level (T1 level) is 2mDBTPDBq-II and PCBN. Since the energy level is more than 0.1 eV lower than the triplet excited state of BB, [Ir( [Ir(dppm)2(acac)] and [Ir(dppm)2(acac)] are in triplet excited states. After the state changes to the triplet excited state of 2mDBTPDBq-II and PCBNBB, The probability of migration is small. In particular, [Ir(dppm)2(acac)] has a probability of 0.18 electrons. Since [Ir(dppm)2(acac)] is lower than [Ir(mppr-M e)2(dpm)].

[0172] Figure 5(A) shows the molecular structure of 2mDBTPDBq-II. The constituent atoms of the six-membered aromatic ring are atoms with higher electronegativity than carbon, such as nitrogen atoms (heteroatoms). When a hetero atom is introduced, the π electrons on the ring are attracted to the hetero atom, and the aromatic ring becomes electron deficient. The area A enclosed by the dotted line in the figure indicates the area where π electrons are lacking, and the electron Generally, heteroaromatic compounds with six-membered rings tend to act as N-type hosts.

[0173] Figure 5(B) shows the molecular structure of PCBNBB. Generally, the nitrogen atom is attached to a benzene ring. When it is outside the aromatic ring and bonded to the ring, the nitrogen atom's lone electron pair is donated to the benzene ring. This results in an excess of electrons, which makes it easier to release electrons (that is, easier to trap holes). In the figure, the area B surrounded by the dotted line indicates the area where π electrons are in excess. Generally, aromatic amine compounds tend to act as P-type hosts. water.

[0174] In addition, there is a 0.47 eV gap between the LUMO of 2mDBTPDBq-II and PCBNBB. There is a relatively large gap of 0.42 electron volts between the HOMO and the HOMO. The gap acts as a barrier to electrons and holes, allowing carriers to pass through the light-emitting layer without recombining. Such a barrier height is 0.3 eV or more, preferably 0.3 eV or more. It should be 0.4 electron volts or higher.

[0175] Whether an N-type host and a P-type host form an exciplex or not depends on the photoluminescence The photoluminescence spectrum of the resulting exciplex can be measured. When the absorption spectrum of the guest overlaps with that of the other guest, an energy transfer process occurs via the Förster mechanism. It can be said that it is easy to do so.

[0176] Figures 6(A) and 6(B) show the results of [Ir(dppm)2(acac)] dissolved in dichloromethane. The UV-visible absorption spectrum of the solution (absorption spectrum 0) is shown below. Using an ultraviolet-visible spectrophotometer (JASCO Corporation, V550 model), The solution (0.093 mmol / L) was placed in a quartz cell and measurements were carried out at room temperature.

[0177] Also, Figures 6(A) and 6(B) show the photomicrographs of the thin film of 2mDBTPDBq-II. Luminescence spectrum (Emission spectrum 1), photoluminescence of a thin film of PCBNBB Emission spectrum (Emission spectrum 2), and 2mDBTPDBq-II and PCBN Photoluminescence spectrum (Emission spectrum 3) of a thin film of the BB mixed material. The ratio of 2mDBTPDBq-II to PCBNBB in the thin film of the mixed material was 0.8:0. It was 2.

[0178] In FIG. 6(A), the horizontal axis represents wavelength (nm), and the vertical axis represents molar absorption coefficient ε (M -1 · cm -1 ) and luminescence intensity (arbitrary units). In FIG. 6(B), the horizontal axis represents energy (eV), and the vertical axis represents the molar extinction coefficient ε (M -1 ·cm -1 ) and luminescence intensity (arbitrary unit ) is shown.

[0179] From the absorption spectrum of Figure 6(A), [Ir(dppm)2(acac)] is It can be seen that there is a broad absorption band near m. This absorption band is the absorption band that strongly contributes to the emission. It is thought to be a convergence.

[0180] Emission spectrum 3 has a longer wavelength (lower energy) than emission spectrum 1 and emission spectrum 2. ) side. The peak of the emission spectrum 3 is Compared to the peak in spectrum 2, it is closer to the absorption band of [Ir(dppm)2(acac)]. Specifically, the absorption spectrum of [Ir(dppm)2(acac)] is The difference between the peak and the peak of emission spectrum 3 was 0.02 eV.

[0181] The emission spectrum of the mixture of 2mDBTPDBq-II and PCBNBB is It was found that the spectrum has a peak on the longer wavelength (lower energy) side. Therefore, by mixing 2mDBTPDBq-II and PCBNBB, exciplexes were formed. It was also suggested that 2mDBTPDBq-II and PCBNBB alone No emission peaks due to 2mDBTPDBq-II and PCBNBB were observed. This means that even if excited, it immediately forms an exciplex.

[0182] The peak in the emission spectrum of the mixed material is the absorption peak of [Ir(dppm)2(acac)]. There is a large overlap with the absorption band that is thought to strongly contribute to the emission in spectrum 0. 2mDBTPDBq-II and PCBNBB with [Ir(dppm)2(acac)] In light-emitting devices with this structure, the energy transfer efficiency from the exciplex to the guest molecule is high. It is suggested. [Example]

[0183] In this example, a light-emitting element according to one embodiment of the present invention was fabricated and its characteristics were evaluated. In the example light-emitting device, 2DBTPDBq-II was used as the N-type host and PCBA1BP was used.

[0184] The layer structure of the light-emitting device fabricated in this example is, from above toward the substrate, a negative electrode, an electron injection layer, an electrode The electron transport layer, the first layer (layer of N-type host), the light-emitting layer (having both N-type host and P-type host) It has a structure consisting of a first layer (p-type host layer), a second layer (p-type host layer), a hole injection layer, and a positive electrode.

[0185] The chemical formulas (structural formulas) of the materials used in this example, including these, are shown below. The materials already mentioned will be omitted.

[0186] [ka]

[0187] A method for fabricating the light-emitting element of this example will be described below. First, a film containing silicon oxide was formed on a glass substrate. A film of indium tin oxide (ITSO) was formed by sputtering to form a positive electrode. The film thickness was 110 nm and the electrode area was 2 mm x 2 mm.

[0188] Next, as a pretreatment for forming a light emitting element on the substrate, the substrate surface was washed with water and After baking at ℃ for 1 hour, UV ozone treatment was performed for 370 seconds. -4 Pa degree The substrate is introduced into a vacuum deposition apparatus whose inside is decompressed to 300°C, and the substrate is heated in a heating chamber of the vacuum deposition apparatus. After vacuum baking at 170° C. for 30 minutes, the substrate was allowed to cool for about 30 minutes.

[0189] Next, the substrate on which the positive electrode was formed was placed in a vacuum deposition apparatus with the surface on which the positive electrode was formed facing downwards. The substrate was fixed to the substrate holder provided in the -4 Under reduced pressure of 100 Pa, DBT3P- The hole injection layer was formed by co-evaporating II and molybdenum (VI) oxide. , 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was 4:2 (=DB The concentration was adjusted to be T3P-II: molybdenum oxide).

[0190] Next, a second layer made of PCBA1BP was evaporated onto the hole injection layer to a thickness of 20 nm. The film was formed by deposition.

[0191] Furthermore, PCBA1BP, 2DBTPDBq-II, and [Ir(dppm)2(acac) ]) was co-evaporated to form an emitting layer on the second layer. The weight ratio of CBA1BP and [Ir(dppm)2(acac)]] was 0.8:0.2: The thickness of the light-emitting layer was adjusted to 40 nm.

[0192] Next, 2DBTPDBq-II for each light-emitting element was evaporated onto the light-emitting layer to a thickness of 10 nm. The first layer was formed by the above method.

[0193] Next, bathophenanthroline (abbreviation: BPhen) was applied to the first layer to a thickness of 20 nm. The electron transport layer was formed as follows.

[0194] Furthermore, lithium fluoride (LiF) was evaporated onto the electron transport layer to a thickness of 1 nm, and electron injection A layer was formed.

[0195] Finally, aluminum was vapor-deposited to form a negative electrode with a thickness of 200 nm. In the above-mentioned deposition process, the deposition was all carried out by a resistance heating method. The element structure of the light-emitting element obtained as described above is shown in Table 2.

[0196] [Table 2]

[0197] The light emitting element is sealed in a glove box with a nitrogen atmosphere so that it is not exposed to the atmosphere. After the work was completed, the operating characteristics of the light-emitting device were measured. The experiment was carried out in an atmosphere maintained at 25°C.

[0198] Figure 7(A) shows the current density dependence of the luminance of the obtained light-emitting device, and Figure 7(B) shows the voltage dependence of the luminance. The luminance dependence of the current efficiency is shown in FIG. 7(C). are shown in Table 3. Approximately 1000 cd / m 2 The voltage required to obtain this brightness is extremely low (2.6V ) and a highly efficient light-emitting device with a power efficiency of 70% or more was obtained.

[0199] [Table 3] [Example]

[0200] In this example, a light-emitting element of one embodiment of the present invention was manufactured and measured. The N-type host was 2mDBTPDBq-II, and the P-type host was PCBA1. A light-emitting device was fabricated using BP.

[0201] The layer structure of the light-emitting device fabricated in this example is the same as that of the light-emitting device in Example 1. The materials used are the same as those already explained. Furthermore, the fabrication method is the same as the actual one except for the N-type host. The same as in Example 1 (i.e., 2DBTPDBq-II in Example 1 was replaced with 2mDBTPDB q-II), so details are omitted. The structure of I is shown below.

[0202] [ka]

[0203] The element structure of the obtained light-emitting element is shown in Table 4.

[0204] [Table 4]

[0205] Figure 8(A) shows the current density dependence of the luminance of the obtained light-emitting device, and Figure 8(B) shows the voltage dependence of the luminance. The luminance dependence of the current efficiency is shown in FIG. 8(C). is shown in Table 5. Approximately 1000 cd / m 2 The voltage required to obtain this brightness is extremely low (2.7V ) and a highly efficient light-emitting device with an external quantum efficiency of 25% or more was obtained. It is said that the upper limit of external quantum efficiency is about 20% due to the extraction efficiency. By using the GCCH concept, it is possible to obtain a light-emitting device with an external quantum efficiency of over 25%. can be done.

[0206] [Table 5] [Explanation of symbols]

[0207] 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 molecules 106 N-type transition region 107 P-type transition region 108 Negative electrode 109 Positive electrode 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 Electronic Relay Layer 118 Composite layer 201 Vacuum Chamber 202 First evaporation source 203 Secondary evaporation source 204 The third evaporation source 205 board 206 Substrate 207 Substrate 211 Vacuum Chamber 212 First evaporation source 213 Secondary evaporation source 214 The third evaporation source 215 The fourth evaporation source 216 The fifth evaporation source 217 Substrate 218 PCB 219 PCB 223 Opening

Claims

1. a light-emitting layer, a first layer, and a second layer between a first electrode and a second electrode; the first layer is provided between the first electrode and the light-emitting layer, the second layer is provided between the second electrode and the light-emitting layer, the light-emitting layer includes a phosphorescent compound, a first organic compound, and a second organic compound; the first organic compound is a compound having a six-membered aromatic ring containing a heteroatom as a ring constituent element, the second organic compound is a carbazole derivative, the first layer includes the first organic compound; the second layer comprises the second organic compound; the first layer does not contain the second organic compound; the second layer does not contain the first organic compound; the first organic compound and the second organic compound are a combination that forms an exciplex in an excited state, a light-emitting device in which the emission spectrum of the exciplex overlaps with the absorption band located on the longest wavelength side of the phosphorescent compound;

2. In claim 1, A light-emitting device in which a region in which the ratio of the first organic compound to the second organic compound changes continuously is provided between the first layer and the light-emitting layer or between the second layer and the light-emitting layer.

3. a first layer and a second layer between the first electrode and the second electrode; the first layer comprises a first organic compound; the second layer comprises a second organic compound; the first layer does not contain the second organic compound; the second layer does not contain the first organic compound; a region having the first organic compound, the second organic compound, and a phosphorescent compound between the first layer and the second layer; the first organic compound is a compound having a six-membered aromatic ring containing a heteroatom as a ring constituent element, the second organic compound is a carbazole derivative, the first organic compound and the second organic compound are a combination that forms an exciplex in an excited state, a light-emitting device in which the emission spectrum of the exciplex overlaps with the absorption band located on the longest wavelength side of the phosphorescent compound;

4. In any one of claims 1 to 3, At least one of the first organic compound and the second organic compound is a fluorescent compound.

5. In any one of claims 1 to 4, The light-emitting device, wherein the phosphorescent compound is an organometallic complex.

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