JP7337369B2 - Organic light emitting device, laminate and light emitting method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laminate having high exciton generation efficiency and an organic light-emitting device using the laminate. The invention also relates to a lighting method.

An organic electroluminescence device (organic EL device) is an organic light-emitting device that emits light by radiative deactivation of excitons generated by current-exciting an organic light-emitting layer. Here, in current excitation, singlet excitons and triplet excitons are generated with a probability of 25%:75% according to the spin statistical law, but the radiative deactivation from the excited triplet state to the ground singlet state is originally This is a forbidden transition. Therefore, in ordinary organic light-emitting materials, triplet excitons are thermally deactivated before they are deactivated by radiation, and only singlet excitons generated with a probability of 25% can be used for light emission. was there.
As a result of vigorous research into light-emitting materials in order to break through the limits of such luminous efficiency, phosphorescent materials that can use triplet excitons for light emission, and triplet excitons that can be converted into singlet excitons have been developed. A thermally activated delayed fluorescence material (TADF) has been developed that can be used for light emission after conversion, and it has become possible to convert singlet and triplet excitons generated by current excitation into light with 100% efficiency. there is

By the way, even with the phosphorescent materials and thermally activated delayed fluorescent materials, the upper limit of the exciton generation efficiency is 100%, which also determines the upper limit of the luminous efficiency of the organic EL element. On the other hand, research has progressed on “singlet fission materials,” in which the singlet exciton splits into two triplet excitons after being excited to an excited singlet state, and the singlet fission material is used as the host of the light-emitting layer. An organic EL device having an exciton generation efficiency of more than 100% by using it as a material has also been proposed (see Patent Document 1).

WO2019/022120

As described above, an organic EL device using a singlet splitting material has been proposed. Specifically, in this organic EL device, after a singlet exciton and a triplet exciton are generated with a probability of 25%:75%, the singlet exciton splits into two triplet excitons. The top 125% of triplet excitons will be generated. Although the exciton generation efficiency of 125% is greatly improved compared to the case where the singlet fission material is not used, it is due to the simple structure in which the singlet fission material is mixed in the light emitting layer. , it was thought that a higher exciton generation efficiency could be obtained.

Under such circumstances, the present inventors have made intensive investigations with the aim of developing a mechanism with a higher theoretical limit value for exciton generation efficiency and dramatically increasing the luminous efficiency of an organic light-emitting device.

As a result of intensive studies, the present inventors came up with the idea of combining reverse intersystem crossing and singlet fission phenomena. That is, after singlet excitons and triplet excitons are generated with a probability of 25%:75% by current excitation, all the generated triplet excitons are converted to singlet excitons by reverse intersystem crossing, and then singlet excitons We conceived of a novel mechanism in which 200% of triplet excitons can be generated theoretically by splitting term excitons. The present invention has been proposed based on such an idea, and specifically has the following configuration.

[1] An organic light emitting device comprising a material capable of converting triplet excitons into singlet excitons and a singlet fission material.
[2] comprising means for suppressing the energy of triplet excitons in the material capable of converting triplet excitons to singlet excitons from directly transferring to the singlet fission material, [1] 3. The organic light-emitting device according to .
[3] The difference ΔE _ST between the lowest excited singlet energy level (E _S1 ) and the lowest excited triplet energy level (E _T1 ) of the material capable of converting triplet excitons to singlet excitons is The organic light-emitting device according to [1] or [2], which is 0.3 eV or less.
[4] having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order; The organic light-emitting device according to any one of [1] to [3].
[5] The organic light-emitting device according to [4], wherein the singlet splitting layer comprises a light-emitting material.
[6] The lowest excited singlet energy level E _S1 of the luminescent material is 0.2 eV higher than the lowest excited singlet energy level E _S1 of the material capable of converting triplet excitons into singlet excitons. The organic light-emitting device according to [5], which is higher than above.
[7] The organic light-emitting device according to [5] or [6], wherein the light-emitting material is a phosphorescent material.
[8] The organic light-emitting device according to any one of [5] to [7], wherein the light-emitting material is a metal complex having a lanthanide as a central metal.
[9] The organic light emitting device according to any one of [4] to [8], wherein the blocking layer has a thickness of 2 to 10 nm.
[10] the lowest excited singlet energy level E _S1 of the material of the blocking layer is 0 lower than the lowest excited singlet energy level E _S1 of the material capable of converting triplet excitons into singlet excitons; The organic light-emitting device according to any one of [4] to [9], which is higher than .2 eV.
[11] the lowest excited triplet energy level _ET1 of the material of the blocking layer is 0 lower than the lowest excited triplet energy level _ET1 of the material capable of converting triplet excitons into singlet excitons; .2 eV or higher, the organic light-emitting device according to any one of [4] to [10].
[12] The organic light-emitting device according to any one of [1] to [11], wherein the material capable of converting triplet excitons into singlet excitons is a delayed fluorescence material.
[13] The singlet splitting layer has a first singlet splitting layer and a second singlet splitting layer, the block layer has a first block layer and a second block layer, and [4] to [12], having a structure in which the singlet splitting layer, the first blocking layer, the exciton generation layer, the second blocking layer, and the second singlet splitting layer of ] The organic light-emitting device according to any one of the above.
[14] The organic light-emitting device according to [13], wherein the first blocking layer contains a hole-transporting material, and the second blocking layer contains an electron-transporting material.
[15] The first blocking layer contains a compound having an aromatic ring in which at least one hydrogen atom is substituted with a substituent bonded to a nitrogen atom, and the second blocking layer contains at least one nitrogen atom. The organic light-emitting device according to [13] or [14], which contains a compound having an aromatic hetero six-membered ring as a ring member.
[16] an anode and a cathode, and a first singlet splitting layer, a first blocking layer, an exciton generation layer, a second blocking layer disposed between the anode and the cathode, in this order from the anode side; and a laminate having a structure in which second singlet splitting layers are stacked in order, wherein the first block layer contains a material having a hole-transport property, and the second block layer has an electron-transport property. The organic light-emitting device according to any one of [1] to [15], comprising a material.
[17] The organic light-emitting device according to any one of [1] to [16], which is an organic electroluminescent device.
[18] A stack having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order body.
[19] current excitation of a material capable of converting triplet excitons to singlet excitons;
The energy of the singlet excitons generated by current excitation and reverse intersystem crossing is transferred to the singlet fission material to generate singlet excitons of the singlet fission material and split the singlet excitons of the singlet fission material. A lighting method comprising:

The organic light-emitting device and light-emitting method of the present invention have a theoretical limit of 200% for exciton generation efficiency, which is extremely high. Therefore, by using the present invention, it is possible to realize a dramatically high luminous efficiency.

FIG. 4 is a schematic diagram for explaining the exciton generation mechanism and the light emission mechanism of the laminate of the present invention. FIG. 3 is a schematic diagram for explaining the exciton generation mechanism and the light emission mechanism of the laminate of the present invention in which a block layer is formed. 1 is a schematic cross-sectional view showing a layer configuration example of an organic electroluminescence element to which a laminate of the present invention is applied; FIG. 1 is an energy level diagram of a laminate 1 produced in Example 1. FIG. 1 is a schematic diagram for explaining an exciton generation mechanism and a light emission mechanism of a laminate 1 produced in Example 1. FIG. 4 is an energy level diagram of a comparative laminate 1 produced in Comparative Example 1. FIG. 3 is a schematic diagram for explaining an exciton generation mechanism and a light emission mechanism of Comparative Laminate 1 produced in Comparative Example 1. FIG. 3 is an energy level diagram of a comparative laminate 2 produced in Comparative Example 2. FIG. 3 is a schematic diagram for explaining the exciton generation mechanism and the light emission mechanism of a comparative laminate 2 produced in Comparative Example 2. FIG. 3 is an energy level diagram of a comparative laminate 3 produced in Comparative Example 3. FIG. 3 shows emission spectra of laminate 1 and comparative laminates 1 to 3. FIG. 4 is an emission spectrum of the organic electroluminescence device produced in Example 2. FIG.

The contents of the present invention will be described in detail below. The constituent elements described below may be explained based on representative embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In this specification, the numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits. Further, the isotopic species of the hydrogen atoms present in the molecule of ^the compound used in the present invention is not ^particularly limited. (deuterium D).
As used herein, the term “fluorescent material” refers to a luminescent material that emits fluorescence with a higher fluorescence emission intensity than that of phosphorescence when the emission is observed at 20° C., and the term “phosphorescent material” It is a luminescent material that emits phosphorescence with a higher intensity than that of fluorescence when luminescence is observed at 20°C. A “delayed fluorescence material” is a material that emits light from an excited singlet, and is a material in which both fluorescence with a short emission lifetime and fluorescence with a long emission lifetime (delayed fluorescence) are observed at 20°C. Ordinary fluorescence (fluorescence that is not delayed fluorescence) is a material that emits light from an excited singlet, and has an emission lifetime of the order of ns. Phosphorescence is a material that emits light from a triplet, and usually has an emission lifetime of μs order or more. In addition, the term “reverse intersystem crossing” as used herein means conversion from triplet excitons to singlet excitons.
In this specification, the thickness of each layer (exciton generation layer, block layer, singlet fission layer, and other layers) constituting the laminate is measured by, for example, a stylus profiling system.

<Organic light-emitting device>
The organic light emitting device of the present invention is characterized by comprising a material capable of converting triplet excitons into singlet excitons and a singlet fission material. The organic light emitting device of the present invention can emit light efficiently by transferring energy from a material capable of converting triplet excitons to singlet excitons to a singlet fission material. More specifically, singlet excitons in a material capable of converting triplet excitons to singlet excitons are transferred to the singlet-splitting material by transferring the energy of the singlet excitons to the singlet-splitting material. By generating and splitting the singlet excitons of the generated singlet-splitting material, triplet excitons can be efficiently obtained for light emission. In the organic light-emitting device of the present invention, phosphorescence may be emitted directly from the singlet-splitting material, or the energy of triplet excitons in the singlet-splitting material may be transferred to the light-emitting material to emit light from the light-emitting material. good.

The “material capable of converting triplet excitons to singlet excitons” in the present invention means that the triplet excitons of the material can be converted to singlet excitons on a one-to-one basis. , and a material that can utilize singlet excitons for light emission. In the present invention, it is not desirable that the material itself capable of converting triplet excitons into singlet excitons emits light. is. Here, one-to-one conversion means conversion of one triplet exciton to one singlet exciton, excluding triplet-triplet annihilation (TTA), for example. In addition, the use of singlet excitons for light emission means that singlet excitons emit fluorescence when returning to the ground state, and the energy of singlet excitons is used to generate excitons in other materials. and ultimately induce luminescence. Therefore, it is possible to convert triplet excitons to singlet excitons one-to-one, and according to the light emission method of the present invention, the energy of the singlet excitons is transferred to the singlet splitting material. Any material that can be used for luminescence corresponds to "a material capable of converting triplet excitons into singlet excitons" regardless of its structure.
As an example of "a material capable of converting triplet excitons into singlet excitons," the difference ΔE _ST between the lowest excited singlet energy level (E _S1 ) and the lowest excited triplet energy level (E _T1 ) is A material that is small and the lowest excited singlet energy level (E _S1 ) and the lowest excited triplet energy level (E _T1 ) are close to each other, so that reverse intersystem crossing from the excited triplet state to the excited singlet state is likely to occur. , a material capable of intersystem crossing from a higher excited triplet energy level (ΔE _Tn ) to the lowest excited singlet energy level (for example, the material described in WO2014185408A1). Materials that actually emit delayed fluorescence and materials that induce delayed fluorescence emission (including so-called assist dopants) are also “materials capable of converting triplet excitons into singlet excitons”. In the following, as a specific example of "a material capable of converting triplet excitons into singlet excitons", "a material having ΔE _ST of 0.3 eV or less" will be described. The constituent elements described below may be explained based on representative embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. Therefore, "a material having a ΔE _ST of 0.3 eV or less" in the following description can be replaced with another "material capable of converting triplet excitons into singlet excitons".

ΔE _ST of _the “material having ΔE _ST of 0.3 eV or less” in the present invention is the difference (E _{S1 −} E _T1 ). "Materials with ΔE _ST of 0.3 eV or less" have the lowest excited singlet energy level (E _S1 ) and the lowest excited triplet energy level (E _T1 ) close to each other, so that the excited triplet state changes to the excited singlet state. It is prone to reverse intersystem crossing to the state. Therefore, by using "a material having ΔE _ST of 0.3 eV or less" as the material of the exciton generation layer, singlet excitons can be efficiently generated in this layer.
Whether the material causes reverse intersystem crossing from the excited triplet state to the excited singlet state can be confirmed by observing the emission of delayed fluorescence. “Delayed fluorescence” is the fluorescence emitted when the excited singlet state returns to the ground state after the reverse intersystem crossing from the excited triplet state to the excited singlet state occurs, and the directly generated excited singlet It is the fluorescence observed later than the fluorescence from the normal state (normal fluorescence).
ΔE _ST of the “material having ΔE _ST of 0.3 eV or less” is preferably 0.2 eV or less, more preferably 0.1 eV or less, and further preferably 0.05 eV or less.
For the method of measuring ΔE _ST , the description in the following section (Method of measuring E _S1 , E _T1 , and ΔE _ST ) can be referred to.

The "singlet fission material" in the present invention means a material in which each singlet exciton generated therein can split into two triplet excitons after transitioning to an excited singlet state.
When a compound undergoes singlet fission, the resulting number of triplet excitons increases. Therefore, the fact that the material is a singlet fission material can be confirmed by using the triplet generation efficiency Φ _ISC as an index. Specifically, solutions containing target compounds to be determined at different concentrations are irradiated with pump light as excitation light, and immediately thereafter, the amount of change ΔABS in absorbance with respect to the probe light is measured. The triplet generation efficiency Φ _ISC obtained from the ΔABS by the following formula (I) shows a correlation that increases as the concentration of the target compound increases, indicating that the target compound is a singlet fission material. can be determined. Here, the "change in absorbance ΔABS" means the change in absorbance based on the absorbance ABS ₀ for the probe light before irradiation with the pump light, and here, for the probe light measured immediately after irradiation with the pump light A value obtained by subtracting ABS ₀ from absorbance ABS _EX . Also, the concentration of the target compound in the solution is selected within a concentration range in which concentration quenching is substantially suppressed. The fact that the material is a singlet fission material may be confirmed by observing a phenomenon or sign indicating an increase in the number of triplet excitons due to singlet fission, or by employing a measurement method other than the above. can be confirmed by

In formula (I), Φ _{I SC} represents the triplet generation efficiency, I ₀ represents the intensity of the pump light irradiated to the solution (excitation light intensity), ΔABS represents the absorbance change (ABS _EX −ABS ₀ ), ε indicates the molar extinction coefficient of the target compound at the pump light wavelength, ε _T indicates the molar extinction coefficient of the target compound at the probe light wavelength, c indicates the concentration of the target compound in solution, and L was used for the measurement. The optical path length of the cell (1 mm) is shown.

The organic light-emitting device of the present invention preferably has a means for suppressing direct transfer of the energy of triplet excitons of the material having ΔE _ST of 0.3 eV or less to the singlet splitting material. The triplet exciton energy referred to herein may be the triplet exciton energy converted from the singlet exciton, or the triplet exciton energy directly generated by current excitation, for example. A means of inhibiting the direct transfer of triplet exciton energy to the singlet-splitting material should be such that more triplet exciton energy would otherwise be transferred to the singlet-splitting material. , the type is not particularly limited. A preferred example of such means is a blocking layer formed between an exciton generation layer containing a material with ΔE _ST of 0.3 eV or less and a singlet fission layer containing a singlet fission material.
The “blocking layer” in the present invention is arranged between the exciton generation layer and the singlet _splitting layer, and the singlet splitting layer Blocks the Dexter transfer of the excited triplet energy to the "singlet fission material" containing, and the exciton generation layer contains "a material having ΔE _ST of 0.3 eV or less", and A layer that allows Förster transfer of excited singlet energy to "term splitting material". The block layer should be a layer in which energy transfer from a material with ΔE _ST of 0.3 eV or less or from a singlet fission material is suppressed. A structure in which an exciton generation layer, a block layer, and a singlet fission layer are laminated in this order is referred to as a "laminate of the present invention".

With the laminate of the present invention having such a configuration, when molecules in the exciton generation layer are excited by externally supplied energy or carriers that cause excitation, singlet excitons are efficiently generated in the exciton generation layer. It is well produced and its excited singlet energy is transferred to the singlet fission layer where the produced singlet exciton splits into two triplet excitons. Therefore, high exciton generation efficiency can be obtained. For example, when the singlet-splitting layer contains a light-emitting material, or when the singlet-splitting material itself emits light, high luminous efficiency can be obtained. The exciton generation mechanism and light emission mechanism will be described below with reference to FIGS. In FIGS. 1 and 2, S ₁ represents the “lowest excited singlet state singlet exciton”, T ₁ represents the “lowest excited triplet state triplet exciton”, and _Sn represents the “lowest excited singlet state”. singlet state singlet excitons” and “higher-order excited singlet state singlet excitons” whose order is 2 to n (n represents a natural number). Also, the energy levels of S ₁ , _Sn , and T ₁ are expressed as E _S1 , E _Sn , and E _T1 , respectively. The energy relationships shown in FIGS. 1 and 2 are examples of energy relationships that can be employed in the present invention, and S ₁ may be _Sn and T ₁ may be T _n . I do not care. That is, the laminate of the present invention should not be construed as being limited to those having such an energy relationship.
Also, in the following description, the value obtained by the following formula (II) is referred to as "exciton generation efficiency".
Formula (II)
Exciton generation efficiency (%) = (N ₁ /N ₀ ) x 100
In equation (II), _N indicates the amount of excitons (initial excitons) generated directly in the exciton generation layer by excitation, and _N indicates the amount of single excitons due to the initial excitons in the subsequent process. It indicates the amount of excitons (secondary excitons) generated in the term splitting layer. However, in the case of the conventional configuration as described in Patent Document 1, that is, in the case of having no exciton generation layer and blocking layer, and having only the singlet splitting layer or the emitting layer alone, N ₀ is , indicates the amount of excitons (initial excitons) generated directly in the singlet-splitting layer or in the emitting layer by excitation, and _N is the amount of excitons generated in the singlet-splitting layer or in the emitting layer due to the initial excitons The sum of the amount of excitons (secondary excitons) generated and the amount of initial excitons remaining without being used for the production of secondary excitons. In any configuration, secondary excitons refer to excitons generated due to initial excitons. singlet excitons, and triplet excitons split from singlet excitons.

As shown in FIGS. 1 and 2, when carriers (h ⁺ , e ⁻ ) are injected into the exciton generation layer of the stack and recombination of carriers occurs in a material with ΔE _ST of 0.3 eV or less, A singlet exciton _S1 and a triplet exciton _T1 are generated with a probability of 25%:75%, and the triplet exciton _T1 undergoes a reverse intersystem crossing from the excited triplet state to the excited singlet state. wakes up and transforms into a singlet exciton S ₁ . The energy of the singlet exciton S ₁ generated in the exciton generation layer moves to the excited singlet energy level E _Sn (n represents a natural number) of the singlet splitting material by the Förster mechanism. On the other hand, since the laminate of the present invention is provided with "a means for suppressing the direct transfer of the energy of triplet excitons of a material having ΔE _ST of 0.3 eV or less to a singlet splitting material", excitation Direct energy transfer of triplet excitons T ₁ generated in the electron generation layer to the singlet fission material is blocked. The excited triplet energy transfer mechanism is the Dexter mechanism, which is different from the excited singlet energy transfer mechanism. Therefore, the energy of triplet excitons T ₁ generated in the exciton generation layer is prevented from moving to the singlet splitting material by providing a blocking layer as shown in FIG. 2, for example. As a result, all of the triplet excitons _T generated with a probability of 75% are subjected to reverse intersystem crossing and converted into singlet excitons _S , and the singlet energy of the excited singlet is also reduced to singlet It moves to the excited singlet energy level E _Sn of the term splitting material. Therefore, theoretically, 100% of the energy of the singlet exciton _S1 and the triplet exciton _T1 generated in a material with ΔE _ST of 0.3 eV or less is the excitation singlet energy of the singlet fission material. It can move to the singlet energy level E _Sn . Then, in the singlet fission material that received the excited singlet energy, a singlet exciton _S1 is generated with an exciton generation efficiency of 100% at the maximum, and each singlet exciton _S1 generates two triplet excitations. The fission into T ₁ produces triplet excitons T ₁ with an exciton production efficiency of 200%. The energy of this triplet exciton T ₁ is transferred to the lowest excited triplet energy level E _T1 of the phosphorescent material and radiatively deactivated, resulting in phosphorescence emission. Here, in this laminate, the triplet exciton generation efficiency is theoretically 200%. , a remarkably high luminous efficiency can be obtained.
Further, if one of the above three layers does not have the exciton generation layer and the blocking layer and has only the singlet fission layer, the injection of carriers into the singlet fission layer causes the singlet In the fission material, singlet excitons and triplet excitons are produced with a probability of 25%:75%, of which the singlet exciton splits into two triplet excitons. In this case, the theoretical limit of triplet exciton generation efficiency is 25%×2+75%=125%, which is much lower than the configuration of the present invention with exciton generation and blocking layers.

As described above, the laminate of the present invention has a high theoretical limit of exciton generation efficiency and exhibits high luminous efficiency by including all of the exciton generation layer, the blocking layer and the singlet splitting layer.
Here, in order to reliably _obtain such an effect, it is necessary to allow the transfer of the excited singlet energy from the material having ΔE _ST of 0.3 eV or less to the singlet splitting material, and at the same time It is important to ensure that the blocking layer prevents the transfer of excited triplet energy from to the singlet-splitting material.
From this point of view, the thickness of the block layer is preferably 2 to 10 nm. Furthermore, the lower limit of the thickness of the blocking layer is more preferably 2.5 nm or more, more preferably 3 nm or more, particularly preferably 5 nm or more, and the upper limit of the thickness of the blocking layer is 10 nm. It is more preferably 8 nm or less, particularly preferably 7 nm or less. If the thickness of the blocking layer is too thin, the energy of the triplet excitons generated in the material with ΔE _ST of 0.3 eV or less will be reduced to the excited triplet energy level E _Tn (n is a natural number) of the singlet splitting material or the light emitting material. ) by the Dexter mechanism. As a result, in materials with ΔE _ST of 0.3 eV or less, the probability of reverse intersystem crossing from the excited triplet state (T ₁ ) to the excited singlet state (S ₁ ) is low, and singlet excitons are generated. unable to grow sufficiently. Conversely, if the thickness of the blocking _layer is too thick _, the _Forster Resonance energy transfer becomes difficult to occur, and the exciton doubling mechanism by the singlet fission material may not work sufficiently.

In addition, the lowest excited singlet energy level E _S1 of the blocking layer material and the light-emitting material is 0.2 eV or more higher than the lowest excited singlet energy level E _S1 of the material having ΔE _ST of 0.3 eV or less. Preferably, it is more preferably higher than 0.3 eV. As a result, energy transfer from the lowest excited singlet energy level E _S1 of the material with ΔE _ST of 0.3 eV or less to the lowest excited singlet energy level E _S1 of the blocking layer material or the light-emitting material is suppressed, The energy of singlet excitons generated in materials with ΔE _ST of 0.3 eV or less is efficiently transferred to the excited singlet energy level E _Sn of the singlet-splitting material. As a result, the exciton doubling mechanism by the singlet fission material can be effectively activated.
The lowest excited triplet energy level _ET1 of the material of the block layer is preferably 0.2 eV or more higher than the lowest excited triplet energy level _ET1 of the material having ΔE _ST of 0.3 eV or less. More preferably, it is higher than 0.3 eV. As a result, the energy of the triplet excitons generated in materials with ΔE _ST of 0.3 eV or less is transferred to the excited triplet energy of the singlet splitting material via energy transfer to the lowest excited triplet energy level E _T1 of the blocking layer. It is possible to avoid moving to the term energy level E _Tn .

Furthermore, the emission peak of the compound having ΔE _ST of 0.3 eV or less overlaps with the light absorption band of the singlet splitting material, and the material of the blocking layer and the light-emitting material absorb light in the overlapping wavelength region. is preferably not shown. As a result, while suppressing the energy transfer from the compound with ΔE _ST of 0.3 eV or less to the blocking layer material and the light emitting material, the energy transfer from the compound with ΔE _ST of 0.3 eV or less to the singlet fission material can be efficiently performed. can be generated.

Although the exciton generation mechanism and the light emission mechanism of the laminate of the present invention have been described above, the mechanism by which the laminate of the present invention exerts its effects is not limited to these mechanisms. For example, in FIGS. 1 and 2, the excited states are limited to “S ₁ ” and “T ₁ ”. Excited singlet state (S ₁ ) and lowest excited triplet state (T ₁ ), but not limited to higher excited singlet states S ₂ , S _{3 .} It may be term states T ₂ , T ₃ . . . T _n . Also in that case, a similar mechanism works to obtain high exciton generation efficiency and high luminous efficiency. When a metal complex is used as a light-emitting material, the excited triplet energy of triplet excitons generated by singlet fission is transferred to the excited triplet energy level E _T1 of the light-emitting material, as well as the light-emitting material ( It may be the energy level of the electronic excited state in the central metal of the metal complex). In addition to this, the light-emitting material may be an organic phosphorescent material or an inorganic phosphorescent material. Furthermore, a material capable of converting triplet excitons into singlet excitons may also be used here so that light is emitted from S _n instead of T _n .

(E _S1 , E _T1 , ΔE _ST measurement method)
“ΔE _ST ” in the present invention is obtained by calculating the lowest excited singlet energy level (E _S1 ) and the lowest triplet energy level (E _T1 ) by the following method and obtaining ΔE _ST =E _S1 -E _T1 value. In addition, if there is a literature value, you may carry out simple examination and consideration using a literature value.
(1) Lowest excited singlet energy level E _S1
A compound to be measured is dissolved in toluene at a concentration of 10 ⁻⁴ M or 10 ⁻⁵ M to prepare a sample, and the fluorescence spectrum of this sample is measured at room temperature (300K). The fluorescence spectrum of this sample is measured at room temperature (300K). Specifically, by accumulating the emission from immediately after the incidence of the excitation light until 100 nanoseconds after the incidence, a fluorescence spectrum is obtained with the emission intensity on the vertical axis and the wavelength on the horizontal axis. A tangent line is drawn to the rising edge of the fluorescence spectrum on the short wavelength side, and the wavelength value λedge [nm] at the intersection of the tangent line and the horizontal axis is obtained. A value obtained by converting this wavelength value into an energy value using the following conversion formula is assumed to be E _S1 .
Conversion formula: E _S1 [eV]=1239.85/λedge
The emission spectrum can be measured, for example, by using a fluorescence spectrophotometer (manufactured by Horiba Ltd., FluoroMax Plus).
(2) lowest excited triplet energy level E _T1
The same sample used for the measurement of the lowest excited singlet energy level E _S1 is cooled to 77 K, the sample for phosphorescence measurement is irradiated with excitation light, and the phosphorescence intensity is measured using a spectrophotometer. Specifically, by accumulating the emission 100 milliseconds after the incidence of the excitation light, a phosphorescence spectrum is obtained with the emission intensity on the vertical axis and the wavelength on the horizontal axis. A tangent line is drawn to the rising edge of the phosphorescence spectrum on the short wavelength side, and the wavelength value λedge [nm] at the intersection of the tangent line and the horizontal axis is obtained. A value obtained by converting this wavelength value into an energy value using the following conversion formula is defined as _ET1 .
Conversion formula: E _T1 [eV]=1239.85/λedge
A tangent line to the rise on the short wavelength side of the phosphorescence spectrum is drawn as follows. First, consider the tangent line at each point on the curve toward the long wavelength side when moving on the spectrum curve from the short wavelength side of the phosphorescence spectrum to the maximum value on the shortest wavelength side among the maximum values of the spectrum. . This tangent line increases in slope as the curve rises (ie as the vertical axis increases). The tangent line drawn at the point where the value of this slope takes the maximum value is taken as the tangent line to the rise on the short wavelength side of the phosphorescence spectrum.
In addition, the maximum point with a peak intensity of 10% or less of the maximum peak intensity of the spectrum is not included in the maximum value on the shortest wavelength side described above, and is closest to the maximum value on the short wavelength side. The tangent line drawn at the point where the value is taken is taken as the tangent line to the rise on the short wavelength side of the phosphorescence spectrum.

The materials and thicknesses of the exciton generation layer, the block layer and the singlet splitting layer used in the laminate of the present invention and the layer structure of the laminate will be specifically described below.

[Exciton generation layer]
The exciton generation layer includes a material with ΔE _ST of 0.3 eV or less. The exciton generation layer may be composed only of materials with ΔE _ST of 0.3 eV or less, or may be composed of materials with ΔE _ST of 0.3 eV or less in addition to materials with ΔE _ST of 0.3 eV or less. It may contain materials other than (other materials).

(Materials with ΔE _ST of 0.3 eV or less)
A delayed fluorescence material can be preferably used as the material having a ΔE _ST of 0.3 eV or less.
Examples of compounds of delayed fluorescence materials that can be used as materials having a ΔE _ST of 0.3 eV or less are given below.

Preferred delayed fluorescence materials include paragraphs 0008 to 0048 and 0095 to 0133 of WO2013/154064, paragraphs 0007 to 0047 and 0073 to 0085 of WO2013/011954, and paragraphs 0007 to 0033 and 0059 to 0066 of WO2013/011955. , paragraphs 0008 to 0071 and 0118 to 0133 of WO2013/081088, paragraphs 0009 to 0046 and 0093 to 0134 of JP 2013-256490, paragraphs 0008 to 0020 and 0038 to 0040 of JP 2013-116975, Paragraphs 0007 to 0032 and 0079 to 0084 of WO2013/133359, paragraphs 0008 to 0054 and 0101 to 0121 of WO2013/161437, paragraphs 0007 to 0041 and 0060 to 0069 of JP 2014-9352, JP 2014 Examples include compounds encompassed by the general formulas described in paragraphs 0008 to 0048 and 0067 to 0076 of JP-A-9224, particularly exemplary compounds that emit delayed fluorescence. Further, JP 2013-253121, WO2013/133359, WO2014/034535, WO2014/115743, WO2014/122895, WO2014/126200, WO2014/136758, WO2014/13 3121 Publications, WO2014/136860, WO2014/196585, WO2014/189122, WO2014/168101, WO2015/008580, WO2014/203840, WO2015/002213, WO2015/ 016200 publication, WO2015/019725, WO2015/072470, WO2015/108049, WO2015/080182, WO2015/072537, WO2015/080183, JP 2015-129240, WO2015/129 714 publication, WO2015/129715, WO2015/133501, WO2015/136880, WO2015/137244, WO2015/137202, WO2015/137136, WO2015/146541, WO2015/15 9541 publication A luminescent material that emits delayed fluorescence can also be preferably employed. The above publications mentioned in this paragraph are hereby incorporated by reference as part of this specification.
These materials having a ΔE _ST of 0.3 eV or less may be used singly or in combination of two or more.

(Materials other than materials with ΔE _ST of 0.3 eV or less)
The exciton generation layer may contain a material (other material) other than the material having ΔE _ST of 0.3 eV or less, if necessary. Other materials can include host materials. When the exciton generation layer contains a host material, the material having ΔE _ST of 0.3 eV or less may be dispersed uniformly in the host material, or may be localized in a part of the host material. good.
When the exciton generation layer contains other materials, the content of the material having ΔE _ST of 0.3 eV or less is preferably 1% by weight or more, preferably 5% by weight, based on the total amount of the materials in the exciton generation layer. It is more preferably 10% by weight or more, and more preferably 10% by weight or more.

(Thickness of exciton generation layer)
Although the thickness of the exciton generation layer is not particularly limited, it is preferably 1 nm to 25 nm, more preferably 3 nm to 20 nm, even more preferably 5 nm to 15 nm.

[Block layer]
As described above, the material of the blocking layer has a lowest excited singlet energy level E _S1 that is 0.2 eV or more than the lowest excited singlet energy level E _S1 of a material with ΔE _ST of 0.3 eV or less. It is preferable to use a high one, and it is more preferable to use a high one of 0.3 eV or more. Furthermore, the material of the blocking layer preferably has a lowest excited triplet energy level _ET1 higher than the lowest excited triplet energy level _ET1 of a material having ΔE _ST of 0.3 eV or less, and Higher than 0.3 eV is more preferable.
Further, when the laminate is used for the light-emitting portion of the organic electroluminescence device, it is preferable to select the material of the block layer in consideration of the carrier transportability. Specifically, the block layer arranged closer to the anode than the exciton generation layer preferably contains a material having a hole-transport property, and the block layer arranged closer to the cathode than the exciton generation layer It preferably contains a material having an electron-transport property.
A compound having an aromatic ring in which at least one hydrogen atom is substituted with a substituent bonded to a nitrogen atom can be given as a material having a hole-transporting property.
Here, the aromatic ring may be a single ring, a condensed ring in which two or more aromatic rings are condensed, or a linked ring in which two or more aromatic rings are linked. When two or more aromatic rings are linked, they may be linked in a straight chain or may be linked in a branched form. The number of carbon atoms in the aromatic ring is preferably 6 to 40, more preferably 6 to 22, still more preferably 6 to 18, even more preferably 6 to 14, and 6 to 10. is particularly preferred. Specific examples of aromatic rings include benzene ring, naphthalene ring, and biphenyl ring.
Examples of substituents bonded at a nitrogen atom include a substituted or unsubstituted diphenylamino group and a structure in which the phenyl groups of a substituted or unsubstituted diphenylamino group are linked together via a single bond or a linking group (e.g., an alkylene group, etc.). A heteroaryl group having a three-ring structure can be mentioned.
A compound having an aromatic six-membered ring containing at least one nitrogen atom as a ring member can be given as an electron-transporting material. Here, the aromatic hetero six-membered ring includes a pyridine ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring and a triazine ring.
Preferred examples of compounds that can be used as the material for the block layer are given below.

These block layer materials may be used singly or in combination of two or more.
In addition, considering the combination with the material having ΔE _ST of 0.3 eV or less, the material of the block layer satisfies the above preferable energy relationship with the material having ΔE _ST of 0.3 eV or less. Select is preferred. Preferred combinations of a material having a ΔE _ST of 0.3 eV or less and a block layer material include the combination of ACR-XTN and mAP and the combination of ACR-XTN and B3PyMPM used in the examples described later. , a combination of DACT-II and mCP, a combination of DACT-II and PPF, a combination of DMAC-TRZ and mCP, a combination of DMAC-TRZ and Bphen, and the like.
The above description can be referred to for the preferred range of the thickness of the block layer.

[Singlet fission layer]
The singlet-splitting layer includes singlet-splitting material. The singlet-splitting layer may be composed only of the singlet-splitting material, or may contain a material other than the singlet-splitting material (another material) in addition to the singlet-splitting material.

(Singlet fission material)
As described above, a singlet fission material is a material in which each singlet exciton produced therein can split into two triplet excitons after transitioning to an excited singlet state. The lowest excited singlet energy level E _S1 of the singlet splitting material is preferably lower than the lowest excited singlet energy level E _S1 of the material with ΔE _ST of 0.3 eV or less. Specifically, the lowest excited singlet energy level E(f) _S1 of the singlet-splitting material is less than the lowest excited singlet energy level E(f) _S1 of the material with ΔE _ST of 0.3 eV or less. It is more preferably 0.1 eV or more, and more preferably 0.2 eV or more. In addition, it is more preferable that the emission spectrum of the material with ΔE _ST of 0.3 eV or less and the absorption spectrum of the singlet splitting material sufficiently overlap. As a result, the energy of singlet excitons generated in a material with ΔE _ST of 0.3 eV or less can be easily transferred to the lowest excited singlet energy level E _S1 of the singlet-splitting material. The emission peak wavelength of the material with ΔE _ST of 0.3 eV or less and the absorption peak wavelength of the singlet splitting material are preferably within 100 nm, more preferably within 50 nm, and even more preferably within 30 nm.
Examples of compounds that can be used as singlet fission materials include acenes such as anthracene, tetracene, and pentacene. These acenes have at least one hydrogen atom substituted with a substituted or unsubstituted aryl group, an alkenyl group substituted with a substituted or unsubstituted aryl group, or an alkynyl group substituted with a substituted or unsubstituted aryl group. may have been For the description, preferred range, and specific examples of the substituted or unsubstituted aryl group, reference can be made to the description, preferred range, and specific examples of the substituted or unsubstituted aryl group for R ¹ in general formula (1) below. .

Preferred examples of compounds that can be used as the singlet fission material are given below.

A compound represented by the following general formula (1) can also be used as the singlet fission material.

In general formula (1), R ¹ represents a substituted or unsubstituted aryl group. One of ^R2 and ^R3 is a hydrogen atom, and the other represents a substituted or unsubstituted aryl group. The substituted or unsubstituted aryl group represented by one of R ² and R ³ and the substituted or unsubstituted aryl group represented by R ¹ may be the same or different, but are preferably the same. The aryl group referred to in the "substituted or unsubstituted aryl group" (in the case of a substituted aryl group, the portion excluding the substituent) preferably has a ring skeleton-constituting atoms of 6 to 26, more preferably 6 to 22, and 6 to 18. is more preferred. Specific examples of the aryl group include a phenyl group, 1-naphthalenyl group, 2-naphthalenyl group, 1-anthracenyl group, 2-anthracenyl group, 9-anthracenyl group, 1-tetracenyl group, 2-tetracenyl group, 5-tetracenyl group, A 1-pyrenyl group and a 2-pyrenyl group can be mentioned.
The aryl groups that R ¹ to R ³ can take may be substituted or unsubstituted, but at least one of R ¹ to R ³ is preferably an unsubstituted aryl group. , R ¹ to R ³ are all preferably unsubstituted aryl groups. When the aryl group has a substituent, the substituent is preferably an alkyl group or an aryl group. Alkyl groups may be linear, branched, or cyclic. The number of carbon atoms is preferably 1-20, more preferably 1-10, still more preferably 1-6. Examples include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group and the like. As for the preferred range and specific examples of the aryl group, the preferred range and specific examples of the aryl group referred to in the above "substituted or unsubstituted aryl group" can be referred to. In addition, the alkyl group and aryl group which are substituents may be further substituted, and preferred examples of the substituent in this case include alkyl groups and aryl groups.
The total carbon number of the substituted or unsubstituted aryl groups that R ¹ to R ³ can take is preferably 6-32, more preferably 6-28, even more preferably 6-24. Examples of substituted aryl groups that R ¹ to R ³ can have include alkylphenyl groups (tolyl group, tert-butylphenyl group, etc.), biphenyl groups, alkylbiphenyl groups (methylbiphenyl group, tert-butylbiphenyl group, etc.), tertyl Phenyl group, alkylterphenyl group (methylterphenyl group, tert-butylterphenyl group, etc.), phenylnaphthyl group, alkylnaphthyl group (methylnaphthyl group, tert-butylnaphthyl group, etc.), phenylanthracenyl group, naphthylanthra Senyl group, alkylanthracenyl group (methylanthracenyl group, tert-butylanthracenyl group, etc.), phenyltetracenyl group, naphthyltetracenyl group, alkyltetracenyl group (methyltetracenyl group, tert-butyltetracenyl group, etc.), phenylpyrenyl group, naphthylpyrenyl group, alkylpyrenyl group (methylpyrenyl group, tert-butylpyrenyl group, etc.).

Specific examples of the compound represented by formula (1) are illustrated below.

These singlet fission materials may be used singly or in combination of two or more.

(Materials other than singlet fission materials)
The singlet-splitting layer may contain materials other than the singlet-splitting material (other materials) as needed. Other materials include light-emitting materials and host materials.
When the singlet-splitting layer contains a light-emitting material, the energy of triplet excitons generated by singlet fission in the singlet-splitting material can be transferred to the light-emitting material by the Dexter mechanism, and the light-emitting material can emit light. In the laminate of the present invention, triplet excitons are generated with high exciton generation efficiency in the singlet splitting layer, so that the light-emitting material can emit light efficiently.

As the light-emitting material, a light-emitting organic compound that can receive energy from triplet excitons and use that energy to emit light can be used. It may be a phosphorescent material or a delayed fluorescent material.

A phosphorescent material, which is a metal complex, receives the energy of triplet excitons, transitions to the lowest excited triplet energy level _ET1 , and deactivates from the lowest excited triplet energy level _ET1 to the ground singlet state. may emit phosphorescence along with , or receive the energy of the triplet exciton and transition to a higher-energy electronic state (electronic excited state) in the central metal, and from that electronic excited state, the original may emit phosphorescence accompanying the transition to the electronic state of (ground electronic state). The phosphorescent material has the lowest excited triplet energy level E _T1 in order to facilitate the transfer of excited triplet energy from triplet excitons generated by singlet fission and to confine the excited triplet energy in the molecule. is lower than the lowest excited triplet energy level E _T1 of the triplet exciton generated by singlet fission, or the energy level of the electronic excited state in the central metal is the triplet excitation generated by singlet fission Those lower than the lowest excited triplet energy level E _T1 of electrons can be preferably used. The phosphorescent material, which is a metal complex, is preferably a metal complex with a lanthanide as a central metal, more preferably a metal complex with Er as a central metal.

In addition, the delayed fluorescence material receives the energy of triplet excitons and transitions to the lowest excited triplet energy level, then transitions to the lowest excited singlet energy level due to reverse intersystem crossing, and the lowest excited singlet energy Delayed fluorescence is emitted with deactivation from the level. Therefore, the delayed fluorescence material used for the light-emitting material has an energy difference ΔE _ST between the lowest excited singlet energy level and the lowest excited triplet energy level of 0.3 eV or less, and the triplet excitation generated by singlet fission The lowest excited triplet energy level E _T1 is the lowest excited triplet exciton produced by singlet fission in order to facilitate the excited triplet energy transfer from the electron and to confine the excited triplet energy within the molecule. It is preferably lower than the triplet energy level E _T1 .

The wavelength of light emitted by the light-emitting material (emission wavelength) is not particularly limited, and may be, for example, a visible region or a near-infrared region. Since the emission wavelength is in the visible region, it is possible to apply the laminate to a light emitting part such as a display device that displays images, characters, symbols, etc., and lighting, and the emission wavelength is in the near infrared region. As a result, the laminate can be applied to near-infrared sensors and light sources used in bioimaging.

Preferred examples of compounds that can be used as the light-emitting material are given below. In the formula below, Ar represents an aryl group.

These luminescent materials may be used singly or in combination of two or more.
Moreover, when the singlet splitting layer contains a light emitting material, the light emitting material may be dispersed uniformly in the singlet splitting layer, or may be localized in a part of the region.
The content of the light-emitting material in the singlet splitting layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, or 50% by weight, based on the total amount of the material in the singlet splitting layer. % or less, more preferably 20 wt % or less, and even more preferably 10 wt % or less.

(Thickness of singlet splitting layer)
The thickness of the singlet splitting layer is not particularly limited, but is preferably 1 nm to 20 nm, more preferably 3 nm to 15 nm, even more preferably 5 nm to 10 nm.

[Layer structure of laminate]
The laminate of the present invention has a structure in which an exciton generation layer, a block layer and a singlet fission layer are laminated in order. The laminate of the present invention may be configured by laminating only these three layers in order, or may have other layers. Other layers may be arranged between the exciton generation layer and the blocking layer, between the blocking layer and the singlet fission layer, on the opposite side of the exciton generation layer from the blocking layer, or between the singlet fission layer. It may be arranged on the side opposite to the block layer. Further, the other layer may be a layer selected from an exciton generation layer, a blocking layer and a singlet fission layer, or may be a layer other than these layers. When a layer selected from an exciton generation layer, a block layer, and a singlet fission layer is provided as other layers, the materials and composition ratios of the exciton generation layers, the block layers, and the singlet fission layers may differ. , the thickness may be the same or different.
A preferable layer structure of the laminate is a three-layer structure consisting of exciton generation layer/block layer/singlet splitting layer, first singlet splitting layer/first block layer/exciton generation layer/second block layer. / A 5-layer structure consisting of a second singlet splitting layer can be mentioned. Here, the first singlet splitting layer and the second singlet splitting layer each correspond to a "singlet splitting layer", and the first block layer and the second block layer each correspond to a "block layer". Equivalent to. The first singlet splitting layer and the second singlet splitting layer, and the first block layer and the second block layer may be the same or different in material, composition ratio, and thickness. Further, each layer constituting the laminate may have a single-layer structure or a multi-layer structure.

As described above, the laminate of the present invention has a high theoretical limit value of exciton generation efficiency, and when a light-emitting material is added to the singlet-splitting layer, compared to the singlet-splitting layer alone to which the light-emitting material is added, Therefore, the luminous efficiency can be dramatically improved. Therefore, by using the laminate of the present invention as a light-emitting portion of an organic photoluminescence device (organic PL device) or an organic electroluminescence device (organic EL device), an organic light-emitting device with high luminous efficiency can be provided.
An organic photoluminescence element has a structure in which at least a light emitting portion is formed on a substrate. An organic electroluminescence device has a structure in which at least an anode, a cathode, and an organic layer are formed between the anode and the cathode. The organic layer includes at least the light-emitting portion, and may consist of only the light-emitting portion, or may have one or more organic layers in addition to the light-emitting portion. Such other organic layers can include hole transport layers, hole injection layers, electron blocking layers, hole blocking layers, electron injection layers, electron transport layers, exciton blocking layers, and the like. The hole transport layer may be a hole injection transport layer having a hole injection function, and the electron transport layer may be an electron injection transport layer having an electron injection function. A structural example of a specific organic electroluminescence element is shown in FIG. 3, 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a light emitting portion, 6 is an electron transport layer, and 7 is a cathode.
Each member and each layer of the organic electroluminescence element will be described below. The description of the substrate and the light-emitting portion also applies to the substrate and the light-emitting portion of the organic photoluminescence element.

(substrate)
The organic electroluminescence device of the present invention is preferably supported by a substrate. The substrate is not particularly limited as long as it is conventionally used in organic electroluminescence devices, and for example, substrates made of glass, transparent plastic, quartz, silicon, or the like can be used.

(anode)
As the anode in the organic electroluminescence device, an electrode material having a large work function (4 eV or more), a metal, an alloy, an electrically conductive compound, or a mixture thereof is preferably used. Specific examples of such electrode materials include metals such as Au, conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ and ZnO. A material such as IDIXO (In ₂ O ₃ --ZnO) that is amorphous and capable of forming a transparent conductive film may also be used. The anode may be formed by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering, and then forming a pattern of a desired shape by photolithography. ), a pattern may be formed through a mask having a desired shape during vapor deposition or sputtering of the electrode material. Alternatively, when a coatable material such as an organic conductive compound is used, a wet film forming method such as a printing method or a coating method may be used. When emitting light from the anode, the transmittance is desirably greater than 10%, and the sheet resistance of the anode is preferably several hundred Ω/□ or less. Furthermore, although the film thickness depends on the material, it is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.

(cathode)
On the other hand, as the cathode, an electrode material having a small work function (4 eV or less) metal (referred to as an electron-injecting metal), an alloy, an electrically conductive compound, or a mixture thereof is used. Specific examples of such electrode materials include sodium, sodium-potassium alloys, magnesium, lithium, magnesium/copper mixtures, magnesium/silver mixtures, magnesium/aluminum mixtures, magnesium/indium mixtures, aluminum/aluminum oxide (Al ₂ O ₃ ) mixtures, indium, lithium/aluminum mixtures, rare earth metals, etc.; Among these, from the viewpoint of electron injection properties and durability against oxidation, etc., a mixture of an electron injection metal and a second metal which is a stable metal having a larger work function value than the electron injection metal, such as a magnesium/silver mixture, Magnesium/aluminum mixtures, magnesium/indium mixtures, aluminum/aluminum oxide (Al ₂ O ₃ ) mixtures, lithium/aluminum mixtures, aluminum and the like are suitable. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. Also, the sheet resistance of the cathode is preferably several hundred Ω/□ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm. In order to transmit the emitted light, it is convenient if either the anode or the cathode of the organic electroluminescence element is transparent or semi-transparent because the emission luminance is improved.
In addition, by using the conductive transparent material mentioned in the explanation of the anode for the cathode, a transparent or semi-transparent cathode can be produced, and by applying this, an element in which both the anode and the cathode are transparent can be produced. can be made.

(Light-emitting part)
The light-emitting part is composed of the laminate of the present invention, and after recombination of holes and electrons injected from each of the anode and the cathode in the exciton generation layer of the laminate to generate excitons, It is a layer that emits light. For the description of the laminate of the present invention, the description in the section <Laminate> above can be referred to. As described above, the laminate of the present invention has a high theoretical limit value of exciton generation efficiency, so that high luminous efficiency can be obtained by using this laminate in the light emitting portion. The laminate constituting the light-emitting portion of the organic electroluminescence element preferably contains a light-emitting material in the singlet splitting layer, and the first singlet splitting layer/first block layer/exciton generation layer/second block It is more preferred to have a layer configuration of layer/second singlet splitting layer. The laminate is arranged so that the first singlet-splitting layer is on the anode side and the second singlet-splitting layer is on the cathode side. When a laminate having such a layer structure is used in the light-emitting portion of an organic electroluminescence device, of the first block layer and the second block layer, the block layer (the first block layer) located on the anode side of the exciton generation layer layer) preferably contains a material having a hole-transporting property, and the blocking layer (second blocking layer) located closer to the cathode than the exciton generating layer preferably contains a material having an electron-transporting property. For the preferred range and specific examples of the material having hole-transporting property and the material having electron-transporting property, the description in the section of (blocking layer) can be referred to.

In the organic light-emitting device and organic electroluminescent device of the present invention, light emission originates from the light-emitting material contained in the singlet splitting layer. This emission may be phosphorescence emission or delayed fluorescence emission. Further, part of the emitted light may be emitted from the material of the exciton generation layer, the material of the block layer, and the singlet splitting material of the singlet splitting layer.

(Injection layer)
An injection layer is a layer provided between an electrode and an organic layer in order to reduce driving voltage and improve luminance of light emission. and between the cathode and the light-emitting portion or the electron-transporting layer. An injection layer can be provided as required.

(blocking layer)
The blocking layer is a layer capable of blocking diffusion of charges (electrons or holes) and/or excitons present in the light-emitting portion to the outside of the light-emitting portion. An electron blocking layer can be disposed between the light-emitting portion and the hole-transporting layer to block electrons from passing through the light-emitting portion toward the hole-transporting layer. Similarly, a hole-blocking layer can be disposed between the light-emitting portion and the electron-transporting layer to block holes from passing through the light-emitting portion toward the electron-transporting layer. Blocking layers can also be used to block excitons from diffusing out of the emitter. That is, each of the electron blocking layer and the hole blocking layer can also function as an exciton blocking layer. The term "electron blocking layer" or "exciton blocking layer" as used herein is used to include a layer having the functions of an electron blocking layer and an exciton blocking layer.

(Hole blocking layer)
A hole-blocking layer has the function of an electron-transporting layer in a broad sense. The hole-blocking layer transports electrons while blocking holes from reaching the electron-transporting layer, thereby improving the recombination probability of electrons and holes in the light-emitting portion. As the material for the hole-blocking layer, the material for the electron-transporting layer, which will be described later, can be used as needed.

(Electron blocking layer)
The electron blocking layer has a function of transporting holes in a broad sense. The electron-blocking layer has the role of transporting holes and blocking the electrons from reaching the hole-transporting layer, thereby improving the probability of recombination of electrons and holes in the light-emitting part. .

(exciton blocking layer)
The exciton-blocking layer is a layer that prevents excitons generated by the recombination of holes and electrons in the light-emitting region from diffusing into the charge-transporting layer. It is possible to effectively confine the light in the light-emitting portion, and the light-emitting efficiency of the device can be improved. The exciton-blocking layer can be inserted either on the anode side or the cathode side adjacent to the light-emitting portion, or both can be inserted at the same time. That is, when the exciton blocking layer is provided on the anode side, the layer can be inserted between the hole transport layer and the light-emitting portion, adjacent to the light-emitting portion. The layer can be interposed between the transport layer and adjacent to the light emitting portion. In addition, a hole injection layer, a hole transport layer, an electron blocking layer, or the like can be provided between the anode and the exciton blocking layer adjacent to the anode side of the light emitting section. An electron injection layer, an electron transport layer, a hole blocking layer, and the like can be provided between the exciton blocking layer adjacent to the cathode side. When the blocking layer is provided, at least one of the excited singlet energy and excited triplet energy of the material used as the blocking layer is preferably higher than the excited singlet energy and excited triplet energy of the light-emitting material.

(Hole transport layer)
The hole-transporting layer is made of a hole-transporting material having a function of transporting holes, and the hole-transporting layer can be provided as a single layer or multiple layers.
The hole transport material has either hole injection or transport or electron blocking properties, and may be either organic or inorganic. Known hole-transporting materials that can be used include, for example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, carbazole derivatives, indolocarbazole derivatives, polyarylalkane derivatives, pyrazoline and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, Examples include amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, especially thiophene oligomers. Aromatic tertiary amine compounds and styrylamine compounds are preferably used, and aromatic tertiary amine compounds are more preferably used.

(Electron transport layer)
The electron transport layer is made of a material having a function of transporting electrons, and the electron transport layer can be provided as a single layer or multiple layers.
The electron transporting material (which may also serve as a hole blocking material) may have a function of transmitting electrons injected from the cathode to the light emitting portion. Electron-transporting layers that can be used include, for example, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, oxadiazole derivatives, and the like. Furthermore, among the above oxadiazole derivatives, a thiadiazole derivative in which an oxygen atom in the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron-withdrawing group can also be used as the electron-transporting material. Furthermore, polymer materials in which these materials are introduced into the polymer chain or these materials are used as the main chain of the polymer can also be used.

The method of forming each layer of the laminate and other layers constituting the organic electroluminescence element is not particularly limited, and may be produced by either a dry process or a wet process.

Preferable materials that can be used for the organic electroluminescence device are specifically exemplified below. However, materials that can be used in the present invention are not limited to the following exemplary compounds. Moreover, even compounds exemplified as materials having specific functions can be used as materials having other functions.

First, preferred compounds that can be used as the host material when the exciton generation layer and the singlet splitting layer contain the host material are listed.

Preferred examples of compounds that can be used as hole injection materials are given below.

Next, preferred examples of compounds that can be used as the hole-transporting material are given.

Preferred examples of compounds that can be used as the electron blocking material are given below.

Preferred examples of compounds that can be used as the hole-blocking material are given below.

Next, preferred examples of compounds that can be used as the electron-transporting material are given.

Next, preferred examples of compounds that can be used as the electron injection material are given.

Examples of preferred compounds as materials that can be added are given below. For example, it may be added as a stabilizing material.

The organic electroluminescence device produced by the method described above emits light by applying an electric field between the anode and cathode of the obtained device. At this time, if the emission is due to excited triplet energy, a wavelength corresponding to the energy level is confirmed as phosphorescence. In the case of luminescence due to excited singlet energy, light with a wavelength corresponding to the energy level is confirmed as fluorescence luminescence and delayed fluorescence luminescence. In addition, since normal fluorescence has a shorter fluorescence lifetime than delayed fluorescence emission, the emission lifetime can be distinguished between fluorescence and delayed fluorescence.

The organic electroluminescence element can be applied to any of a single element, an element having a structure arranged in an array, and a structure having anodes and cathodes arranged in an XY matrix. According to the present invention, by using the laminate of the present invention in the light-emitting portion, an organic light-emitting device with greatly improved exciton generation efficiency and luminous efficiency can be obtained. An organic light-emitting device such as an organic electroluminescence device using the laminate of the present invention can be applied to various uses. For example, it is possible to manufacture an organic electroluminescence display device using this organic electroluminescence element. You can refer to it. In particular, this organic electroluminescence device can also be applied to organic electroluminescence lighting and backlights, which are in great demand.

The features of the present invention will be described more specifically with reference to examples below. The materials, processing details, processing procedures, etc. described below can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below. The absorption characteristics were evaluated using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-2600), and the emission characteristics were evaluated using a spectrophotometer (Horiba Corporation, FluoroMax Plus) and a source meter (Keithley Co.) 2400 series), external quantum efficiency measurement device (Hamamatsu Photonics, C9920-12), absolute quantum efficiency measurement device (Hamamatsu Photonics, C9920-02), compact fluorescence lifetime measurement device (Hamamatsu Photonics, C11367-21) was used.

<Compounds used in Examples>
The compounds used in this example are shown below.

The lowest excited singlet energy level E _S1 and the lowest excited triplet energy level E _T1 of ACR-XTN, mAP, B3PyMPM, rubrene and Er(hfa), and ^{the 4} I _13/2 level of Er(hfa) Table 1 shows. In Table 1, the lowest excited singlet energy level E _S1 and the lowest excited triplet energy level E _T1 of ACR-XTN are the literature values described in Nakanotani et al., Nat. Commun., 2014, 5, 4016. and the lowest excited singlet energy level E _S1 and the lowest excited triplet energy level E _T1 of mAP are the literature values described in Seo et al., Dye Pigment., 2015, 254, and the lowest of B3PyMPM The excited singlet energy level E _S1 and the lowest excited triplet energy level E _T1 are literature values described in Sasabe et al., Adv. Mater, 2011, 21, 336, and are the lowest excited singlet energy of rubrene. The level E _S1 and the lowest excited triplet energy level E _T1 are literature values described in Nagata et al., Adv. The potential E _S1 , the lowest excited triplet energy level E _T1 , ^{the 4} I _13/2 level are literature values described in Ahmed et al., Inorg. Chem. Acta, 2012, 392, 165.

In addition, when the emission spectrum of ACR-XTN and the absorption spectra of mAP, B3PyMPM, rubrene and Er(hfa) were measured, it was found that the emission peak of ACR-XTN and the light absorption band of rubrene overlapped. It was confirmed that B3PyMPM, rubrene compounds and Er(hfa) do not exhibit light absorption in the wavelength region.

(Example 1) Fabrication and Evaluation of Laminate 1 Consisting of First Singlet Splitting Layer/First Blocking Layer/Exciton Generation Layer/Second Blocking Layer/Second Singlet Splitting Layer on Quartz Substrate , each thin film was laminated at a degree of vacuum of less than 10 ^-4 Pa by a vacuum deposition method.
First, on a quartz substrate, rubrene and Er(hfa) were vapor-deposited from different vapor deposition sources to form a first singlet splitting layer with a thickness of 10 nm. Here, the Er(hfa) concentration was set to 2.0% by weight. Then, on the first singlet splitting layer, mAP is evaporated to form a 2 nm thick first blocking layer, on which ACR-XTN is evaporated to form a 15 nm thick exciton blocking layer. A product layer was formed. Furthermore, B3PyMPM was deposited thereon to form a second blocking layer with a thickness of 2 nm. Then, on the second blocking layer, rubrene and Er(hfa) were deposited from different deposition sources to form a second singlet splitting layer with a thickness of 10 nm. At this time, the concentration of Er(hfa) was set to 2.0% by weight. Through the above steps, a laminate 1 having a five-layer structure was obtained.
FIG. 4 shows an energy level diagram of the produced laminate 1, and FIG. 5 shows an estimated light emission mechanism. In the energy level diagram shown in FIG. 4, the numerical value shown below each layer is the absolute value of the HOMO (Highest Occupied Molecular Orbital) energy level of that layer, and the numerical value shown above each layer is the It is the absolute value of the LUMO (Lowest Unoccupied Molecular Orbital) energy level of the layer, and the unit is "eV". The meaning of this numerical value is the same in FIGS.
As shown in FIG. 5, in the laminate 1, when ACR-XTN in the exciton generation layer is excited to generate singlet excitons S ₁ and triplet excitons T ₁ , the triplet excitons T ₁ are reverse term crossover and convert to singlet exciton S ₁ . The energy of the singlet excitons S ₁ generated by ACR-XTN passes through the first block layer or the second block layer to the first singlet splitting layer or the second singlet splitting layer by the Forster mechanism. moves to the lowest excited singlet energy level E _S1 of the contained rubrene (singlet splitting material). On the other hand, the excited triplet energy transfer mechanism is the Dexter mechanism. Therefore, energy transfer from triplet excitons T ₁ to rubrene is blocked by the first blocking layer and the second blocking layer. Therefore, at most 100% of the triplet excitons T ₁ generated in ACR-XTN are subjected to reverse intersystem crossing and converted to the excited singlet state S ₁ . 2 to the lowest excited singlet energy level E _S1 of the rubrene contained in the singlet splitting layer. In rubrene that has received the excited singlet energy, the singlet exciton _S1 splits into two triplet excitons _T1 , and the excited triplet energy is transferred to ^Er4I of Er(hfa) by the Dexter mechanism. Move to the _13/2 level. Phosphorescence is emitted along with the relaxation from ^{the 4} I _13/2 level to ^{the 4} I _15/2 level. Thus, the energies of the excitons S ₁ and T ₁ generated in the exciton generation layer of the laminate 1 are maximum, and all of them are transferred as excited singlet energy to the lowest excited singlet energy level E _{S1 of} rubrene. , where each singlet exciton S ₁ produced splits into two triplet excitons T ₁ . Therefore, the theoretical limit value of the exciton generation efficiency of the laminate 1 is 200%.

(Comparative Example 1) Fabrication and Evaluation of Comparative Laminate 1 Consisting of First Singlet Splitting Layer/Exciton Generation Layer/Second Singlet Splitting Layer Do not form first block layer and second block layer A comparative laminate 1 was produced in the same manner as in Example 1 except for the above.
FIG. 6 shows an energy level diagram of the manufactured comparative laminate 1, and FIG. 7 shows an estimated light emission mechanism. where ACR-XTN in FIG. 6 corresponds to the material with ΔE _ST ≦0.3 eV in FIG. 7, rubrene in FIG. 6 corresponds to the singlet fission material in FIG. It corresponds to the phosphorescent material in FIG.
As shown in FIG. 7, in this comparative laminate 1, since it does not have the first block layer and the second block layer, the energy of the singlet exciton _S1 generated in the exciton generation layer and the triplet exciton Together, the energy of T ₁ is transferred to the singlet-splitting material (rubrene) in the first or second singlet-splitting layer, where singlet excitons S ₁ and triplet A term exciton T ₁ is produced. Of these, the singlet exciton S ₁ splits into two triplet excitons T _{1 ,} and the excited triplet energy is used for phosphorescence emission of Er(hfa). As such, the excited triplet energy is utilized for phosphorescence emission of Er(hfa). Here, the exciton generation efficiency of the comparative laminate 1 is obtained by setting the ratio of the singlet exciton S ₁ and the triplet exciton T ₁ in the exciton generation layer in the equilibrium state to (100−R _T ):R _T , (100−R _T )×2+R _T =200−R _T , and the theoretical limit value of the exciton generation efficiency is lower than that of the laminate 1 .

(Comparative Example 2) Fabrication and Evaluation of Comparative Laminate 2 Consisting of First Emitting Layer/Exciton Generation Layer/Second Emitting Layer Instead of Forming First Singlet Splitting Layer and Second Singlet Splitting Layer A comparative laminate 2 was prepared in the same manner as in Example 2, except that only Er(hfa) was used as a vapor deposition source to form the first and second light emitting layers each having a thickness of 10 nm.
FIG. 8 shows an energy level diagram of the manufactured comparative laminate 2, and FIG. 9 shows an estimated light emission mechanism. Here, ACR-XTN in FIG. 8 corresponds to the material with ΔE _ST ≦0.3 eV in FIG. 9, and Er(hfa) in FIG. 8 corresponds to the phosphorescent material in FIG.
As shown in FIG. 8, this comparative laminate 2 does not have the first block layer and the second block layer, and rubrene (singlet splitting material) is used in the first light emitting layer and the second light emitting layer. ). Also, as shown in FIG. 9, the lowest excited singlet energy level E _S1 of the phosphorescent material (Er(hfa)) is ΔE _ST ≦0.3 eV, and the lowest excited singlet energy level of the material (ACR-XTN) higher than the energy level E _S1 . Therefore, among the energies of the excitons generated in the exciton generation layer, the energy of the triplet excitons T ₁ moves to ^{the 4} I _13/2 level of the phosphorescent material (Er(hfa)), resulting in phosphorescence emission. Although utilized, the energy of the singlet exciton S ₁ cannot be transferred to the phosphorescent material (Er(hfa)) and does not contribute to phosphorescence emission. Here, the exciton generation efficiency of the comparative laminate 2 is defined as the ratio of singlet excitons S ₁ and triplet excitons T ₁ in the exciton generation layer in the equilibrium state (100−R _T ):R _T R _T becomes the upper limit, and the theoretical limit value of the exciton generation efficiency becomes a much lower value than that of the laminate 1 .

(Comparative Example 3) Fabrication and evaluation of singlet splitting layer alone A singlet splitting layer having a thickness of 20 nm was formed on a quartz substrate using the same method as in Example 1.
FIG. 10 shows an energy level diagram of the fabricated singlet splitting layer.
In this singlet fission layer, there is no energy transfer from the exciton generation layer, and triplet excitons generated in the singlet fission layer Er(hfa) emits phosphorescence only by the energy of the electrons and triplet excitons directly generated by excitation of the singlet splitting layer. The exciton generation efficiency of _{this comparative} laminate ₃ is given by ₍ 100−R _T )×2+R _T =200−R _T is the upper limit, and the theoretical limit value of the exciton generation efficiency is lower than that of the laminate 1 .

FIG. 11 shows emission spectra of the singlet-splitting layers produced in Laminate 1, Comparative Laminates 1 and 2, and Comparative Example 3 with excitation light of 400 nm. Here, FIG. 11(a) is the emission spectrum in the range of 450-700 nm, and FIG. 11(b) is the emission spectrum in the range of 1400-1650 nm.
In FIG. 11(a), the emission peak around 510 nm originates from the emission of ACR-XTN, and the emission peak around 560 nm originates from the emission of rubrene. Further, in FIG. 11(b), the emission peak near 1500 nm is derived from the emission of Er(hfa).
As shown in FIG. 11, Er(hfa)-containing rubrene layers (first and second singlet splitting layers), mAP layer (first blocking layer), ACR-XTN layer (exciton generation layer), Laminate 1 including all B3PyMPM layers (second blocking layers) exhibited higher intensity of luminescence derived from Er(hfa) than luminescence derived from ACR-XTN and rubrene. On the other hand, in Comparative Laminate 1, which does not have a blocking layer, the intensity of light emitted from Er(hfa) is lower than in Laminate 1. This is probably because the excited triplet energy generated in ACR-XTN is also transferred to rubrene, so that the exciton doubling mechanism by singlet splitting of rubrene does not work sufficiently. On the other hand, the laminate of Comparative Example 2, which did not use rubrene, had a high emission intensity derived from ACR-XTN, and a lower intensity of emission derived from Er(hfa) than that of the laminate 1. The reason why the emission intensity derived from ACR-XTN is high is considered to be that the excited singlet energy generated by ACR-XTN was not transferred to Er (hfa) and was used for the emission of ACR-XTN. The reason why the emission intensity derived from (hfa) is low is considered to be that the excited singlet energy generated by ACR-XTN does not contribute to the emission of Er(hfa) at all. Furthermore, the singlet splitting layer produced in Comparative Example 3 had the lowest emission intensity derived from Er(hfa) among the produced layers. This is because there is no exciton generation layer to supply singlet excitons to the singlet fission layer.
From the above, by using a structure in which an exciton generation layer, a blocking layer, and a singlet fission layer are stacked in order, the exciton amplification effect of the singlet fission material works effectively, and the phosphorescence emission efficiency is remarkable. was found to improve to

(Example 2) Production of an organic electroluminescence device having a laminate consisting of a first singlet splitting layer/first blocking layer/exciton generating layer/second blocking layer/second singlet splitting layer Evaluation Each thin film was laminated at a degree of vacuum of less than 10 ⁻⁴ Pa by a vacuum deposition method on a glass substrate on which an anode made of indium tin oxide (ITO) with a thickness of 100 nm was formed.
First, TAPC was formed on ITO to a thickness of 50 nm.
Next, on the TAPC layer, a rubrene layer (first singlet splitting layer) containing 2.0% by weight of Er(hfa) and an mAP layer (first blocking layer) were formed in the same manner as in Example 1. , an ACR-XTN layer (exciton generation layer), a B3PyMPM layer (second blocking layer), and a rubrene layer containing 1.8% by weight of Er(hfa) (second singlet splitting layer). to form a laminate.
Subsequently, B3PyMPM was formed to a thickness of 55 nm on the laminate. Furthermore, 8-quinolinatolithium (Liq) was formed to a thickness of 0.8 nm, and aluminum (Al) was deposited thereon to a thickness of 80 nm to form a cathode, thereby forming an organic electroluminescence device. .
FIG. 12 shows the emission spectrum of the produced organic electroluminescence device. As shown in FIG. 12, an emission peak around 1500 nm derived from Er(hfa) emission could also be observed from the organic electroluminescence device to which the laminate of the present invention was applied.

The laminate of the present invention has a high theoretical limit of exciton generation efficiency. Therefore, by using the laminate of the present invention in the light-emitting portion of an organic light-emitting device, the light-emitting efficiency can be dramatically improved. Therefore, the present invention has high industrial applicability.

1 Substrate 2 Anode 3 Hole Injection Layer 4 Hole Transport Layer 5 Light Emitting Part 6 Electron Transport Layer 7 Cathode

Claims (14)

having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order;
The blocking layer inhibits Dexter transfer of excited triplet energy from the material capable of converting triplet excitons to singlet excitons to the singlet splitting material, and from the triplet excitons a layer that allows Förster transfer of excited singlet energy from a material capable of conversion to singlet excitons to said singlet splitting material;
the singlet splitting layer further comprising a light-emitting material;
the lowest excited singlet energy level E _S1 of the luminescent material is 0.2 eV or more higher than the lowest excited singlet energy level E _S1 of the material capable of converting triplet excitons to singlet excitons ; Organic light-emitting device. 2. The organic light-emitting device according to claim 1 , wherein said light-emitting material is a phosphorescent material. having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order;
The blocking layer inhibits Dexter transfer of excited triplet energy from the material capable of converting triplet excitons to singlet excitons to the singlet splitting material, and from the triplet excitons a layer that allows Förster transfer of excited singlet energy from a material capable of conversion to singlet excitons to said singlet splitting material;
the singlet splitting layer further comprising a light-emitting material;
An organic light-emitting device, wherein the light-emitting material is a metal complex having a lanthanide as a central metal. The organic light emitting device according to any one of claims 1 to 3 , wherein the blocking layer has a thickness of 2 to 10 nm. having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order;
The blocking layer inhibits Dexter transfer of excited triplet energy from the material capable of converting triplet excitons to singlet excitons to the singlet splitting material, and from the triplet excitons a layer that allows Förster transfer of excited singlet energy from a material capable of conversion to singlet excitons to said singlet splitting material;
The lowest excited singlet energy level E _S1 of the material of the blocking layer is 0.2 eV or more than the lowest excited singlet energy level E _S1 of the material capable of converting triplet excitons into singlet excitons. Expensive , organic light-emitting device. The lowest excited triplet energy level _ET1 of the material of the blocking layer is 0.2 eV or more than the lowest excited triplet energy level _ET1 of the material capable of converting triplet excitons into singlet excitons. The organic light-emitting device according to any one of claims 1 to 5, which is high. The organic light-emitting device according to any one of claims 1 to 6 , wherein the material capable of converting triplet excitons into singlet excitons is a delayed fluorescence material. having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order;
The blocking layer inhibits Dexter transfer of excited triplet energy from the material capable of converting triplet excitons to singlet excitons to the singlet splitting material, and from the triplet excitons a layer that allows Förster transfer of excited singlet energy from a material capable of conversion to singlet excitons to said singlet splitting material;
The singlet splitting layer has a first singlet splitting layer and a second singlet splitting layer, the block layer has a first block layer and a second block layer, and the first singlet An organic light-emitting device having a structure in which a splitting layer, the first blocking layer, the exciton generation layer, the second blocking layer, and the second singlet splitting layer are laminated in this order. 9. The organic light-emitting device according to claim 8 , wherein the first blocking layer contains a hole-transporting material, and the second blocking layer contains an electron-transporting material. The first blocking layer contains a compound having an aromatic ring in which at least one hydrogen atom is substituted with a substituent bonded to a nitrogen atom, and the second blocking layer contains at least one nitrogen atom as a ring member. 10. The organic light-emitting device according to claim 8 or 9 , comprising a compound having an aromatic hetero six-membered ring. an anode and a cathode; a first singlet-splitting layer disposed between the anode and the cathode and containing a singlet-splitting material; a first blocking layer; a laminate having a structure in which an exciton generation layer containing a material capable of being converted into electrons, a second blocking layer, and a second singlet fission layer containing a singlet fission material are laminated in order; The first blocking layer contains a material having hole-transporting properties, and the second blocking layer contains a material having electron-transporting properties,
The blocking layer inhibits Dexter transfer of excited triplet energy from the material capable of converting triplet excitons to singlet excitons to the singlet splitting material, and from the triplet excitons An organic light-emitting device, which is a layer that allows Förster transfer of excited singlet energy from a material capable of conversion to singlet excitons to said singlet splitting material. The organic light-emitting device according to any one of claims 1 to 11 , which is an organic electroluminescence device. having a structure in which an exciton generation layer containing a material capable of converting triplet excitons into singlet excitons, a block layer, and a singlet fission layer containing a singlet fission material are stacked in this order;
The blocking layer inhibits Dexter transfer of excited triplet energy from the material capable of converting triplet excitons to singlet excitons to the singlet splitting material, and from the triplet excitons a layer that allows Förster transfer of excited singlet energy from a material capable of conversion to singlet excitons to said singlet splitting material;
The lowest excited singlet energy level E _S1 of the material of the blocking layer is 0.2 eV or more than the lowest excited singlet energy level E _S1 of the material capable of converting triplet excitons into singlet excitons. Tall, laminate. A light emitting method for causing the laminate according to claim 13 to emit light,
current excitation of a material capable of converting triplet excitons to singlet excitons;
transferring the energy of singlet excitons generated by current excitation and reverse intersystem crossing to the singlet fission material to generate singlet excitons of the singlet fission material;
A method of emitting light comprising splitting singlet excitons of a singlet splitting material.