CN112736208B - Organic electroluminescent device and display device - Google Patents

Organic electroluminescent device and display device Download PDF

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CN112736208B
CN112736208B CN202011639484.6A CN202011639484A CN112736208B CN 112736208 B CN112736208 B CN 112736208B CN 202011639484 A CN202011639484 A CN 202011639484A CN 112736208 B CN112736208 B CN 112736208B
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triplet
organic electroluminescent
electroluminescent device
excited
tta
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CN112736208A (en
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段炼
蔡明瀚
王宏宇
曹方义
张跃威
李国孟
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Tsinghua University
Kunshan Govisionox Optoelectronics Co Ltd
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Abstract

The invention provides an organic electroluminescent device and a display device, the organic electroluminescent device includes a light emitting layer; the luminescent layer comprises a wide band gap material, a TTA material and a resonance type TADF material; the first excited singlet level of the wide bandgap material is greater than the first excited singlet level of the TTA material, which is greater than the first excited singlet level of the resonant TADF material; the first excited triplet level of the wide bandgap material is greater than the first excited triplet level of the TTA material and the resonant TADF material, the first excited triplet level of the resonant TADF material being greater than the first excited triplet level of the TTA material; wherein the spin-orbit coupling constant SOC of the n-th excited triplet state and the first excited singlet state of the TTA material is more than or equal to 0.30cm ‑1 . The organic electroluminescent device has excellent luminous efficiency, service life and color purity.

Description

Organic electroluminescent device and display device
Technical Field
The invention relates to an organic electroluminescent device and a display device, and belongs to the technical field of organic electroluminescence.
Background
An organic electroluminescent device is a device that achieves light emission by current driving. Specifically, the organic electroluminescent device includes a cathode, an anode, and functional layers such as a light-emitting layer between the cathode and the anode. When a voltage is applied, electrons from the cathode and holes from the anode migrate to the light emitting layer and combine to generate excitons, respectively, thereby emitting light of different wavelengths according to the characteristics of the light emitting layer.
At present, the blue light material for organic electroluminescent devices on the production line is mainly a common triplet-triplet annihilation material (TTA), which utilizes the annihilation effect of triplet excitons to increase the total amount of singlet excitons, and theoretically, the theoretical limit efficiency of TTA can reach 62.5%.
However, the exciton utilization rate in practical process is often far lower than 62.5%, so the efficiency and the service life of the corresponding organic electroluminescent device are often not satisfactory. In addition, the half-peak width of the common TTA is wide at present, which not only can cause the blue light color coordinate not to reach the standard, but also can cause a certain 'blue harm' problem.
Disclosure of Invention
The invention provides an organic electroluminescent device, which can not only improve the exciton utilization rate of a triplet-triplet annihilation material, but also effectively reduce the high-energy exciton concentration in a system by pertinently limiting the composition of a luminescent layer, thereby improving the luminous efficiency, the service life and the color purity of the organic electroluminescent device.
The present invention provides a display device including the above organic electroluminescent device, and thus having excellent luminous efficiency, lifespan, and color purity.
An organic electroluminescent device includes a light emitting layer; the light-emitting layer includes a wide band gap material, a triplet-triplet annihilation material, and a resonance-type thermally activated delayed fluorescence material;
a first excited singlet energy level of the wide band gap material is greater than a first excited singlet energy level of the triplet-triplet annihilation material, which is greater than a first excited singlet energy level of the resonant thermally activated delayed fluorescence material; a first excited triplet energy level of the wide band gap material is greater than a first excited triplet energy level of the triplet-triplet annihilation material and a first excited triplet energy level of the resonant thermally activated delayed fluorescence material, the first excited triplet energy level of the resonant thermally activated delayed fluorescence material being greater than the first excited triplet energy level of the triplet-triplet annihilation material;
wherein the spin-orbit coupling constant SOC of the n-th excited triplet state and the first excited singlet state of the triplet-triplet annihilation material satisfies the following requirement, n is more than or equal to 2 and less than or equal to 6:
SOC≥0.30cm -1 。
alternatively, the triplet-triplet annihilation material has the structure of formula 1,
Figure BDA0002879579230000011
in the formula 1, A is selected from anthryl, naphthyl, perylenyl, pyrenyl, fluorenyl, phenanthryl, fluoranthenyl, benzophenanthryl,
Figure BDA0002879579230000012
One of the group and acenaphthylene, X is independently selected from a group with heteroatom, and m is more than or equal to 1.
Alternatively, in formula 1, X is selected from substituted or unsubstituted C 3 -C 30 Heterocyclic group of (a), C substituted by a functional substituent 6 -C 30 One of the aryl groups of (a); the functional substituent is selected from C 3 -C 30 At least one of a heterocyclic group, a straight chain group containing a hetero atom, and a branched group containing a hetero atom.
Alternatively, in formula 1, the X contains 1-10 heteroatoms.
Optionally, in formula 1, the distance between at least one heteroatom in X and the centroid of A is ≦ 10 angstroms.
Optionally, in formula 1, the distance between at least one heteroatom in X and the centroid of A is ≦ 7 angstroms.
Alternatively, the triplet-triplet annihilation material is a compound having one of the structures shown as a1-a 423.
Alternatively, in the light-emitting layer, the mass of the wide band gap material is 10 to 200% of the mass of the triplet-triplet annihilation material, and the mass of the resonance-type thermally activated delayed fluorescence material is 0.5 to 30% of the mass of the triplet-triplet annihilation material.
Optionally, the thickness of the light emitting layer is 5-100 nm.
The invention also provides a display device comprising the organic electroluminescent device.
The organic electroluminescent device adopts a wide band gap material as a main body material, and a triplet-triplet annihilation material (TTA material) as a sensitizer sensitized resonance type thermal activation delayed fluorescence material (resonance type TADF material) to emit light. The spin-orbit coupling constant SOC of the n-th excited triplet state and the first excited singlet state of the TTA material is higher, so that excitons in the n-th excited triplet state can rapidly cross to the first excited singlet state, the phenomenon of energy loss caused by too low speed of crossing of the excitons in the triplet state to the first excited singlet state is greatly inhibited, the light-emitting efficiency and the service life of the organic electroluminescent device are improved by improving the utilization rate of the excitons, and the efficiency roll-off of the organic electroluminescent device caused by overlong service life of the excitons in the triplet state under high brightness is also reduced. In addition, the resonance type thermal activation delayed fluorescence material without obvious electron transfer in the molecule is used as the dye to emit light, so that the color purity of the organic electroluminescent device has good performance. Meanwhile, the wide-band-gap material can effectively dilute the exciton concentration of the TTA material and the resonance type TADF material, regulate and control the transmission balance of carriers, and enhance the stability of the device.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A first aspect of the present invention provides an organic electroluminescent device comprising an anode, a hole transport region, a light-emitting layer, an electron transport region and a cathode deposited in this order on a substrate.
The substrate, the anode, the hole transport region, the electron transport region, and the cathode may be made of materials commonly used in the art. For example, a glass or polymer material having excellent mechanical strength, thermal stability, water resistance, and transparency; the anode material can be Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), and tin dioxide (SnO) 2 ) Oxide transparent conductive materials such as zinc oxide (ZnO), and any combination thereof; the cathode may be made of magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), or any combination thereof. The light-emitting layer will be described in detail below.
The light-emitting layer of the present invention comprises a wide band gap material, a triplet-triplet annihilation material, and a resonance-type thermally activated delayed fluorescence material; a first excited singlet energy level of the wide band gap material is greater than a first excited singlet energy level of the triplet-triplet annihilation material, which is greater than a first excited singlet energy level of the resonant thermally activated delayed fluorescence material; a first excited triplet energy level of the wide bandgap material is greater than a first excited triplet energy level of the triplet-triplet annihilation material and a first excited triplet energy level of the resonant thermally activated delayed fluorescence material, the first excited triplet energy level of the resonant thermally activated delayed fluorescence material being greater than the first excited triplet energy level of the triplet-triplet annihilation material; wherein the spin-orbit coupling constant SOC of the n-th excited triplet state and the first excited singlet state of the triplet-triplet annihilation material satisfies the following requirement, n is more than or equal to 2 and less than or equal to 6:
SOC≥0.30cm -1 。
in the art, a TTA material is a material that increases the total amount of singlet excitons by utilizing an annihilation effect of the triplet excitons and is capable of emitting fluorescence. Specifically, two triplet excitons collide with each other to form nine possible intermediate states, wherein 1/9 has a singlet characteristic, 1/3 has a triplet characteristic, and 5/9 has a quintet characteristic, and the specific energy path is shown in path 1:
Figure BDA0002879579230000021
since the quintet exciton is extremely unstable and not easy to form, the intermediate 1/4 formed when two triplet excitons collide with each other has singlet characteristics, 3/4 has triplet characteristics, and the two are finally converted into the first excited singlet exciton and the ground state molecule, and the first excited triplet molecule and the ground state molecule, respectively, and the specific energy path is shown in path 2:
Figure BDA0002879579230000022
whereas, if the intermediate state of the TTA material with triplet characteristics in pathway 2 is finally transformed into the first excited singlet and ground state molecules in the form of pathway 3, the theoretical ultimate efficiency of TTA can reach 0.25+ 0.75/2-62.5%.
Figure BDA0002879579230000023
That is, according to route 2, two first excited triplet excitons of the TTA material can generate an intermediate state having a singlet characteristic with a probability of 1/4 and an intermediate state having a triplet characteristic with a probability of 3/4 after colliding with each other. Wherein an intermediate state characterized by a singlet state eventually generates a ground state molecule and a first excited singlet exciton, while an intermediate state characterized by a triplet state presents two sub-paths. The first sub-path (i.e., the energy path of the intermediate state of the triplet character in path 2) is to generate a molecule of ground state and an n (n ≧ 2) th excited triplet exciton, and the newly generated n-th excited triplet exciton may return to the first excited triplet state, or may undergo intersystem crossing to the first excited singlet state and eventually return to the ground state to emit fluorescence; the other sub-path (i.e., path 3) is the direct generation of a first excited singlet molecule and a ground state molecule.
In the invention, a wide band gap material is used as a main body material, and the spin-orbit coupling constant SOC (more than or equal to 0.3 cm) of the nth excited triplet state and the first excited singlet state is adopted -1 ) The higher TTA material is used as a sensitizer sensitization resonance type TADF material to emit fluorescence, so that the luminous efficiency, stability and color purity of the organic electroluminescent device can be effectively improved, and the service life of the organic electroluminescent device is prolonged. Based on the analysis of the phenomenon, the inventor believes that it is possible that the SOC of the TTA material of the present invention is high, so that the speed of the triplet characteristic intermediate state (including the above two sub-paths) crossing to the first excited singlet state system is increased, more first excited triplet excitons can be converted into the first excited singlet state through the TTA process, and energy is transferred to the resonance TADF material to emit fluorescence, and the difference between the actual internal quantum efficiency and the theoretical internal quantum efficiency of the TTA material is reduced, so that the organic electroluminescent device has the advantages of both high efficiency and high color purity. In addition, the triplet excitons with high energy are one of the key reasons for causing the roll-off, and the speed of the triplet characteristic intermediate state of the TTA material of the invention crossing to the first excited singlet state is higher, so that the concentration of the triplet excitons in the system is lower, the service life is shorter, and the roll-off of the organic electroluminescent device of the invention is improved to a certain extent.
The main material is a wide band gap material, the wide band gap material can regulate and control the transmission balance of current carriers, dilute the concentration of a TTA material and a resonance TADF material and effectively reduce the density of excitons, thereby effectively inhibiting exciton-polaron quenching (TPA) and enhancing the stability of a device. Preferably, the difference between the HOMO energy level and the LUMO energy level of the wide bandgap material is more than or equal to 2eV, so that the singlet state and the triplet state of the wide bandgap material can be ensured to be at higher energy levels, and the wide bandgap material can generate heat to the TTA material
Figure BDA0002879579230000032
An energy delivery process and a Dexter energy delivery process.
The invention adopts the resonance type TADF material as the dye, and can further improve the utilization rate of excitons. Because the energy level difference between the first excited singlet state and the first excited triplet state of the resonant TADF material is small, the triplet excitons of the resonant TADF material undergo intersystem crossing to the first excited singlet state and then transition back to the ground state to emit light by absorbing ambient heat; in addition, a part of resonance type TADF materials can not generate triplet excitons with intersystem crossing to the first excited triplet energy level of TTA materials with lower energy levels, so that the concentration of high-energy triplet excitons on the resonance type TADF materials is reduced, the problem that the efficiency of an organic electroluminescent device is seriously reduced under high current density due to the high-energy excitons is further solved, and the stability of the device is further improved to a certain extent.
The resonance type TADF material is a material which has small energy level difference (less than or equal to 0.5ev) between a first excited singlet state and a first excited triplet state, weaker charge transfer in molecules and high stability. For example, a compound having one of the following structures:
Figure BDA0002879579230000031
on one hand, the energy level difference between the first excited singlet state and the first excited triplet state of the resonant TADF material is very small, so that more triplet excitons are easy to undergo up-conversion singlet transfer to generate delayed fluorescence; on the other hand, because the planar aromatic rigid structure and the molecules do not have obvious donor groups and acceptor groups, the planar conjugation is good, the intramolecular charge transfer is weak, and the stability is high, thereby being beneficial to narrowing the spectrum of the device and improving the color purity of the device.
Alternatively, when the SOC is further larger than 0.5cm -1 This is advantageous in further increasing the rate of intersystem crossing of the intermediate state of triplet character of the TTA material to the first excited singlet state.
Hereinafter, the energy transfer and the light emitting process of the organic electroluminescent device according to the present invention will be described in detail.
The luminescent layer of the organic electroluminescent device comprises a wide-bandgap host material, a TTA material and a resonance TADF material. Wherein the first excited singlet energy level of the wide bandgap material is greater than the first excited singlet energy level of the TTA material, which is greater than the first excited singlet energy level of the resonant TADF material; the first excited triplet energy level of the wide bandgap material is greater than the first excited triplet energy level of the TTA material and the first excited triplet energy level of the resonant TADF material, which is greater than the first excited triplet energy level of the TTA material. Therefore, after the organic electroluminescent device is electrically excited, holes and electrons are directly recombined on the wide band gap material, and then the first excited singlet state exciton and the first excited triplet state exciton of the wide band gap material can respectively cross to the first excited singlet state and the first excited triplet state of the TTA material; alternatively, the holes and electrons recombine on the TTA material, generating singlet excitons and first excited triplet excitons on the TTA material. The first excited triplet excitons of the TTA material annihilate two by two to generate singlet excitons and excitons of intermediate states with triplet characteristics, and because the spin-orbit coupling constants SOC of the nth excited triplet state and the first excited singlet state of the TTA material of the present invention are high, the rate of intersystem crossing of the excitons of intermediate states with triplet characteristics to the first excited singlet state is fast, thereby enabling more intermediate states with triplet characteristics to transit to the first excited singlet state.
Because the first excited singlet energy level of the TTA material is greater than the first excited singlet energy level of the resonant TADF material, excitons in the first excited singlet state in the TTA material will be excited toward the first excited singlet state of the resonant TADF material
Figure BDA0002879579230000042
In contrast, most triplet excitons of the resonant TADF material can undergo intersystem crossing to transit to the first excited singlet state, and some electrons that do not reach the occurrence of intersystem crossing can transit to the first excited triplet state of the TTA material in a lower energy state. Therefore, the triplet excitons and the singlet excitons in the wide band gap material, TTA material and resonance type TADF material in the light-emitting layer are efficiently utilized,and finally returning to the ground state from the first excited singlet state of the resonance type TADF material to generate fluorescence, thereby improving the luminous efficiency of the organic electroluminescent device.
In addition, the nth excited triplet state exciton in the TTA material can be rapidly transited to the first excited singlet state, and part of electrons which cannot generate reverse intersystem crossing in the resonance TADF material can also be transited to the first excited triplet state of the TTA material with a lower energy state, so that the concentration of the high-energy triplet state exciton in the whole system is low, the service life is short, the efficiency roll-off of the organic electroluminescent device is favorably inhibited, and the color purity is improved. Furthermore, the present invention adopts a resonance type TADF as a dye, which does not have a significant intramolecular charge transfer excited state inside the molecule, and thus can obtain a narrow emission spectrum.
The invention innovates the composition of the organic luminescent layer, enables the TTA material to be used as a sensitizer to assist the wide band gap material to sensitize the resonance type TADF material, can improve the service life of the organic electroluminescent device, reduce roll-off, narrow spectrum and improve color purity, and has very important significance for industrial application.
The wide band gap material of the present invention is a compound including at least one group selected from a carbazolyl group, a carbolinyl group, a spirofluorenyl group, a fluorenyl group, a silicon group, and a phosphinyl group.
The invention is not limited to a specific structure of the wide bandgap material, preferably the wide bandgap material is selected from compounds having one of the following structures:
Figure BDA0002879579230000041
Figure BDA0002879579230000051
the calculation method of the spin-orbit coupling constant SOC between the n-th excited triplet state and the first excited singlet state of the TTA material specifically uses theoretical calculation software such as Gaussian, ADF, Gamess, VASP and the like to calculate the S-state of the TTA material 0 ，S 1 ，T 1 ，T n Or S 1 -T n And after the optimal configuration in the transition state, calculating by software such as Gaussian, ORCA, PySOC, ADF, MOMAP and the like to obtain a spin-orbit coupling constant SOC between the first excited singlet state and the nth excited triplet state of the material.
As described above, the TTA material of the present invention has an SOC of not less than 0.3cm -1 . In one embodiment, the TTA material that satisfies the SOC has a structure of formula 1,
Figure BDA0002879579230000061
in the formula 1, A is selected from anthryl, naphthyl, perylenyl, pyrenyl, fluorenyl, phenanthryl, fluoranthenyl, phenylpropenanthryl,
Figure BDA0002879579230000063
One of the group and acenaphthylene, X is independently selected from a group with heteroatom, and m is more than or equal to 1.
In formula 1, m X may be substituted for the hydrogen atom in a to form a bond with a. Wherein m X's may be different from each other, the same as each other, or partially the same. Optionally, m is an even number, and m xs are identical to each other and symmetrically connected to X, thereby facilitating maintaining the stability of the TTA material.
Anthracenyl, naphthyl, perylenyl, pyrenyl, fluorenyl, phenanthrenyl, fluoranthenyl, phenylpropenanthryl, phenanthrenyl, and the like, represented by A,
Figure BDA0002879579230000064
Acenaphthylene is a material in the art with a TTA luminescent mechanism. The above X is a group having a hetero atom, and the present invention is not limited to a specific structure of X as long as X has a hetero atom, and may be, for example, 1 to 10 hetero atoms. And the number and type of heteroatoms in each X may be independently selected and not before each other. Specifically, the lone pair electrons of the heteroatoms in X can effectively enhance the proportion of n-pi in a single triplet state in the TTA material, so that the TTA material conforming to the structure has the SOC meeting the requirement, and the luminous efficiency, the service life and the color of the organic electroluminescent device can be optimizedAnd (4) purity.
Further, X is selected from a cyclic group in which the ring-forming atoms include a hetero atom or an aromatic group substituted with a group having a hetero atom.
Wherein the cyclic group in which the ring-forming atoms include hetero atoms means substituted or unsubstituted C 3 -C 30 The heterocyclic group of (1). C 3 -C 30 The heterocyclic group of (A) means a cyclic group in which the ring-forming atoms include 3 to 30 carbon atoms and the ring-forming atoms include a hetero atom, C 3 -C 30 The heterocyclic group of (a) can be a heteroaryl group such as pyrimidinyl, pyrazinyl, thienyl, pyrrolyl, carbazolyl, indolyl, indazolyl, pyridyl, acridinyl, pyrazolyl, imidazolyl, thiazolyl, thienyl, and the like, or a non-heteroaryl group such as piperazinyl, furyl, and the like. The invention is not limited to C 3 -C 30 The specific atom bonded to A in the heterocyclic group of (2) may be a heteroatom of the ring-forming atom in X directly bonded to A, or may be another atom of the ring-forming atom of X directly bonded to A. When C is present 3 -C 30 When the heterocyclic group of (A) has a substituent, the present invention is not particularly limited with respect to the kind and number of the substituent, and the substituent may be independently selected from the group consisting of halogen, cyano, and C 1 -C 10 Alkyl of (C) 2 -C 6 Alkenyl of, C 1 -C 6 Alkoxy or thioalkoxy of C 6 -C 30 Aryl of (C) 3 -C 30 One or more of the heteroaryl groups of (a).
An aryl substituted by a group bearing a heteroatom means C substituted by a functional substituent 6 -C 30 Aryl group of (1). The functional substituent in the present invention means C 3 -C 30 A straight chain group containing a hetero atom, a branched group containing a hetero atom. C 3 -C 30 The heterocyclic group is the same as described above and is not described herein; by heteroatom-containing straight chain radical is meant a straight chain radical having from 0 to 30 carbon atoms containing a heteroatom, e.g. -NH 2 、-O-CH 3 、-CH 2 -CH 2 -NH 2 、-CH 2 -O-CH 3 、-NH-CH 3 Etc.; heteroatom-containing branched group means the number of carbon atoms containing a heteroatomBranched radicals of 3 to 30, e.g. -O-CH (CH) 3 )-CH 3 、-CH 2 -CH(NH 2 )-CH 3 、-CH(OH)-CH 3 、-NH-CH(CH 3 )-CH 3 And the like. The invention is not restricted to the substitution of C 6 -C 30 And in addition to the functional substituents, C 6 -C 30 The other hydrogen atoms of the aryl radicals in question may also be simultaneously substituted by non-functional substituents, but it must be ensured that C 6 -C 30 Has a site in the aryl group to replace the hydrogen atom in a.
The heteroatom referred to herein means an atom other than carbon and hydrogen atoms, and the TTA material in which the heteroatom is a nitrogen atom, an oxygen atom, a phosphorus atom, a sulfur atom, a selenium atom, and a tellurium atom is exemplified herein. The inventor finds that for the same group element, the larger the atomic number is, the more remarkable the improvement effect on the organic electroluminescent device is.
Further, the present invention prefers TTA materials with a very strong induction effect. In formula 1, when the distance from at least one heteroatom in X to the centroid of a is less than or equal to 10 angstroms, the TTA material exhibits a stronger induction effect, and lone pair electrons of the heteroatom in X can further enhance the ratio of n-pi in a single triplet state in the TTA material, so that the SOC is larger, and the light-emitting efficiency and the lifetime of the organic electroluminescent device can be further optimized. The SOC of the TTA material is greater when the distance of at least one heteroatom in X to the centroid of a is smaller, e.g., 7 angstroms or less. It can be understood that, when the number of the heteroatoms less than or equal to 10 angstroms away from the centroid of the distance a in X is larger, the more significant the TTA material has effects of improving the light emitting efficiency of the organic electroluminescent device and prolonging the service life of the organic electroluminescent device.
The centroid of a as referred to herein refers to the closest point to all atoms in group a, and in the case of a disubstituted naphthalene, the centroid of a naphthalene group is the closest point to a total of 22 atoms (14 carbon atoms and 8 hydrogen atoms) of the naphthalene, which can be determined, for example, by software such as Gaussian, Mercury, and Diamond (e.g., Centroids function in Mercury). The Distance of each heteroatom from the centroid of the group a in the TTA material having the structure of formula 1 can also be determined by software such as Gaussian, Mercury, and Diamond (e.g., measurement Distance function in Mercury, modification Bond function in Gaussian).
In particular embodiments, the TTA materials of the present invention may be, and are not limited to, compounds described by one of the following structures:
Figure BDA0002879579230000062
Figure BDA0002879579230000071
Figure BDA0002879579230000081
Figure BDA0002879579230000091
Figure BDA0002879579230000101
Figure BDA0002879579230000111
Figure BDA0002879579230000121
Figure BDA0002879579230000131
Figure BDA0002879579230000141
Figure BDA0002879579230000151
Figure BDA0002879579230000161
Figure BDA0002879579230000171
Figure BDA0002879579230000181
Figure BDA0002879579230000191
Figure BDA0002879579230000201
in addition, the performance of the organic electroluminescent device can be further optimized by controlling the proportions of the wide bandgap material, the TTA material, and the resonance type TADF material in the light-emitting layer.
In the implementation process of the invention, the proportion of the wide band gap material, the TTA material and the resonance type TADF material in the luminescent layer is reasonably controlled, which is beneficial to further improving the efficiency and the color purity of the device. The inventors have found that when the mass of the wide bandgap material is 10-200% of the mass of the TTA material, and the mass of the resonant TADF material is 0.5-30% of the mass of the TTA material, the efficiency and lifetime of the organic electroluminescent device are greatly improved.
In general, different host materials and dyes in the light emitting layer in an organic electroluminescent device have an effect on the performance of the device. In the invention, the SOC is more than 0.3cm -1 Respectively as main bodies of TTA material and resonance type TADF materialMaterials and dyes, and thus, generally speaking, excellent efficiency and lifetime of the device can be substantially guaranteed when the mass of the wide bandgap material is 10-100% of the mass of the TTA material, and/or when the mass of the resonant TADF material is 0.5-10% of the mass of the TTA material.
In the organic electroluminescent device, the thickness of the luminescent layer is generally controlled to be 5-100nm, so that the luminous efficiency and the service life of the organic electroluminescent device are ensured.
The hole transport region and the electron transport region of the present invention will be described below. The hole transport region is located between the anode and the light emitting layer. The hole transport region may be a Hole Transport Layer (HTL) of a single layer structure including a single layer containing only one compound and a single layer containing a plurality of compounds. The hole transport region may also be a multilayer structure including at least two layers of a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), and an Electron Blocking Layer (EBL).
The materials of the hole transport region, including HIL, HTL and EBL, may be selected from, but are not limited to, phthalocyanine derivatives such as CuPc, conductive polymers or polymers containing conductive dopants such as polyphenylenevinylene, polyaniline/dodecylbenzenesulfonic acid (Pani/DBSA), poly (3, 4-ethylenedioxythiophene)/poly (4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphorsulfonic acid (Pani/CSA), polyaniline/poly (4-styrenesulfonate) (Pani/PSS), aromatic amine derivatives.
Wherein the aromatic amine derivatives are compounds represented by HT-1 to HT-34 below. If the material of the hole transport region 3 is an aromatic amine derivative, it may be one or more of compounds shown in HT-1 to HT-34 and PH-47 to PH-85.
Figure BDA0002879579230000202
Figure BDA0002879579230000211
Figure BDA0002879579230000221
Figure BDA0002879579230000231
The hole injection layer is located between the anode and the hole transport layer. The hole injection layer may be a single compound material or a combination of a plurality of compounds. For example, the hole injection layer may employ one or more compounds of the above-mentioned HT-1 to HT-34, or employ one or more compounds of the following HI1-HI 3; one or more of the compounds HT-1 to HT-34 may also be used to dope one or more of the compounds HI1-HI3 described below. The thickness of the hole injection layer is generally 5 to 30nm, and the thickness of the hole transport layer is generally 5 to 50 nm.
Figure BDA0002879579230000232
The electron transport region may be an Electron Transport Layer (ETL) of a single-layer structure including a single-layer electron transport layer containing only one compound and a single-layer electron transport layer containing a plurality of compounds. The electron transport region may also be a multilayer structure including at least two layers of an Electron Injection Layer (EIL), an Electron Transport Layer (ETL), and a Hole Blocking Layer (HBL). In one aspect, the electron transport layer material may be selected from, but is not limited to, the combinations of one or more of ET-1 to ET-57 and PH-1 to PH-46 listed below. The thickness of the electron transport layer is generally 5 to 30 nm.
Figure BDA0002879579230000233
Figure BDA0002879579230000241
The light emitting device may further include an electron injection layer between the electron transport layer and the cathode in the structure, and the electron injection layer includes, but is not limited to, one or more of the following combinations. The thickness of the electron injection layer is generally 0.5 to 5 nm.
LiQ,LiF,NaCl,CsF,Li 2 O,Cs 2 CO 3 ,BaO,Na,Li,Ca。
The thicknesses of the various layers described above may be those conventional in the art.
The invention also provides a preparation method of the organic electroluminescent device, which comprises the steps of depositing the anode, the hole transmission area, the luminescent layer, the electron transmission area and the cathode on the substrate in sequence, and then packaging. When the luminescent layer is prepared, the evaporation rate of the wide band gap material, the evaporation rate of the TTA material and the evaporation rate of the resonance type TADF material are adjusted by a multi-source co-evaporation method to enable the dye to reach a preset doping proportion, and the luminescent layer is formed by any one of the above-mentioned methods of the co-evaporation of the wide band gap material source, the TTA material source and the resonance type TADF material source. And the anode, the hole transport region, the electron transport region and the cathode are deposited in the same manner as the prior art.
The embodiment of the invention also provides a display device which comprises the organic electroluminescent device provided as above. The display device can be specifically a display device such as an OLED display, and any product or component with a display function including the display device, such as a television, a digital camera, a mobile phone, a tablet computer, and the like. The display device has the same advantages as the organic electroluminescent device compared with the prior art, and the description is omitted here. For example, the organic electroluminescent device can be used as a red light quantum dot film and a green light quantum dot film in a backlight excitation device, so that the color development area is improved.
The following will describe the specific preparation method of TTA material represented by formula 1 of the present invention in detail by taking a plurality of synthesis examples as examples, but the preparation method of the present invention is not limited to these synthesis examples.
Various chemicals used in the present invention, such as palladium tetratriphenylphosphine, sodium carbonate, toluene, t-butyllithium, tetrahydrofuran, ethanol, and basic chemical materials such as various reaction materials, were purchased from Beijing Bailingwei science and technology Co., Ltd and Beijing Yinaoka science and technology Co., Ltd. 1 H-NMR spectra were obtained by JEOL LtdMeasured by a nuclear magnetic resonance spectrometer JNM-ECA 600. Mass spectra were measured using a high performance liquid-electrospray-ion trap/time-of-flight tandem mass spectrometer from Shimadzu, japan.
Synthesis example 1: synthesis of Compound A4
Figure BDA0002879579230000251
5-bromo-2-phenylpyridine (10g) was dissolved in super-dry tetrahydrofuran (200mL) under argon, and n-butyllithium (2.5M, 17mL) was slowly added to the above solution at-80 ℃. Then, anthracene-9, 10-dione (3.4g) was added in one portion. The resulting mixture was stirred for 2 hours, during which time the temperature was raised to 20 ℃. Subsequently, cold water (100mL) was added and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (100 mL). The organic portion was dried over magnesium sulfate and the volatiles were removed in vacuo to leave a foamy solid. To the solid were added potassium iodide (14g), sodium hypophosphite (10g) and acetic acid (150mL), and the mixture was heated under reflux for 2 h. After cooling, the precipitate was collected and washed with copious amounts of THF/H2O (7: 3). After drying, 3.4g of yellow compound A4 were collected. The compound A4 has a hydrogen spectrum by nuclear magnetic resonance ( 1 HNMR) and High Resolution Mass Spectrometry (HRMS) were characterized as follows:
the compound 1 has a hydrogen spectrum by nuclear magnetic resonance ( 1 HNMR) and High Resolution Mass Spectrometry (HRMS) characterization as follows:
1 H NMR(600MHz,CDCl 3 -d6,δppm):8.86(s,2H),8,208(s,4H),8.085–8.028(m,2H),7.964(d,2H),7.743(s,4H),7.582–7.513(m,6H),7.427(d,4H)；
HRMS(ESI)m/z:[M+H] + calcd for C 36 H 24 N 2 ,484.19；found,485.20.
synthesis example 2: synthesis of Compound A421
Figure BDA0002879579230000252
Under the protection of argon, 9 is added10-bis (3-bromophenyl) anthracene (5.36g), pyridine-3-boronic acid (3.10g), palladium chloride (PdCl) 2 0.266g), triphenyl phosphite (0.786g), potassium carbonate (12.4g), toluene (166mL), ethanol (120mL) and distilled water (153mL) were added to the glass flask in that order. The reaction mixture was heated at reflux for 5h, and the organic portion was separated. The volatiles were removed in vacuo leaving a grey residue which was purified by silica gel column chromatography using petroleum ether/ethyl acetate (1: 1) as eluent. 3.7g of white compound 2 are obtained. Under the protection of argon, 9, 10-bis (3-bromophenyl) anthracene (5.36g), pyridine-3-boric acid (3.10g) and palladium chloride (PdCl) 2 0.266g), triphenyl phosphite (0.786g), potassium carbonate (12.4g), toluene (166mL), ethanol (120mL) and distilled water (153mL) were added to the glass flask in that order. The reaction mixture was heated at reflux for 5h, and the organic portion was separated. The volatiles were removed in vacuo leaving a grey residue which was purified by silica gel column chromatography using petroleum ether/ethyl acetate (1: 1) as eluent. 3.7g of white Compound A421 are obtained.
The compound is prepared by nuclear magnetic resonance hydrogen spectrum ( 1 HNMR) and High Resolution Mass Spectrometry (HRMS) were characterized as follows:
1 H NMR(600MHz,CDCl 3 -d6,δ):8.97(s,2H),8.61(d,J＝7.2Hz,2H),7.97(d,J＝12.4Hz,2H),7.81(s,2H),7.78–7.74(m,8H),7.56(t,J＝10Hz,2H),7.39–7.37(m,6H)；
HRMS(ESI)m/z:[M+H] + calcd for C 36 H 24 N 2 ,484.19；found,485.22.
synthetic example 3: synthesis of Compound A422
Figure BDA0002879579230000253
5- (10-Bromoanthracen-9-yl) -2-phenylpyridine (4.09g), (4- (2-phenyl-1H-benzo [ d ] imidazol-1-yl) phenyl) boronic acid (3.14g) and tetrakis (triphenylphosphine) palladium (0) (1.5g) were dissolved in a mixture of ethanol (50mL) and toluene (100mL) under argon. A solution of sodium carbonate (6.5g) in water (50mL) was added to the solution and stirred at 85 ℃ for 24 h. After cooling to room temperature, water (100mL), dichloromethane (100mL) was added and stirred. After filtering the solution, the solution was partitioned between dichloromethane and water. The product was extracted from the organic layer and evaporated under reduced pressure. The product was purified by column chromatography on silica gel using petroleum ether/ethyl acetate (1: 1) as eluent to give 4.8g of yellow compound A422.
The compound is prepared by nuclear magnetic resonance hydrogen spectrum ( 1 HNMR) and High Resolution Mass Spectrometry (HRMS) were characterized as follows:
1 H NMR(600MHz,CDCl 3 -d6,δ):9.293(d,1H),8.484(d,2H),8.288(d,1H),8.225(d,1H),8.152–8.135(m,1H),7.977–7.905(m,6H),7.804–7.768(m,2H),7.741–7.697(m,4H),7.674–7.607(m,2H),7.588–7.491(m,9H)；
HRMS(ESI)m/z:[M+H]+calcd for C 44 H 29 N 3 ,599.24；found,599.3214.
hereinafter, the organic electroluminescent element according to the present invention will be further described with reference to specific examples.
Embodiments 1 to 30 respectively provide an organic electroluminescent device having a device structure including an ITO anode, a hole injection layer (HATCN, 5nm), a hole transport layer (NPB, 30nm), a light emitting layer, an electron transport layer (Bphen, 30nm), an electron injection layer (LiF, 1nm), and a cathode (Al, 150nm) in this order.
Figure BDA0002879579230000261
Wherein, the composition of the luminescent layer of each organic electroluminescent device is different, and the specific composition and the thickness of the luminescent layer are shown in table 1.
Comparative examples 1 to 8 provide organic electroluminescent devices having device structures in accordance with examples 1 to 8, and parameters of respective functional layers in accordance with examples 1 to 8 substantially in accordance with the same, except that the composition of the light-emitting layer was different from those of the examples. The selection of specific materials is shown in table 1.
The structures of sensitizer materials A1-A6, A9, A10, A12, A419 and A420 in Table 1 are shown as above, the structures of wide bandgap materials w-47, w-48 and w-49 are shown as above, and the structures of A001 and A002 and the structures of dye are shown as below, wherein BD1, BD3-BD6 are resonance type TADF materials, and BD2, BD7 are conventional fluorescent materials.
Figure BDA0002879579230000262
The electrical properties (EQE, spectrum and the like) of the device are obtained by adopting a Keithley2400 test carried by a Japanese Koimangson C9920-12 absolute electroluminescence quantum efficiency test system. The internal quantum efficiency of the material can be obtained by dividing the external quantum efficiency by 0.25, assuming a device light extraction efficiency of 0.25. The lifetime of the devices was tested at 1000nits initial brightness using a model ZJZCL-2 lifetime testing equipment of Shanghai university.
Figure BDA0002879579230000271
Figure BDA0002879579230000281
From table 1 it can be seen that:
1. compared with the comparative example, when the SOC is more than 0.3cm -1 When the TTA material is used as a sensitizer, the organic electroluminescent device has small efficiency roll-off under high brightness, narrower half-peak width and better color purity, and meanwhile, the device has high luminous efficiency and longer service life, and the overall characteristics of the device are obviously superior to those of comparative examples 1-8;
2. from examples 1 to 7 (the central group is an anthracene group, and the heteroatom is N), it can be seen that the larger the SOC is, the more excellent the overall performance of the organic electroluminescent device is;
although the SOC of the TTA material in example 22 is higher than that of the TTA material in example 3, the device performance of example 22 is slightly worse than that of example 3, probably because: compared with a nitrogen-containing heterocyclic ring, the TTA material in the embodiment 22 has poor stability of the methoxy group containing the heteroatom, so that the TTA material has some negative influence on the performance of the device in the embodiment 22;
although the SOC of the TTA material in example 24 was higher than that of the TTA material in example 6, the device performance of example 24 was slightly worse than that of example 6, probably because: the TTA material in example 24 has too many free mobile groups compared to the TTA material in example 6, and thus the TTA material in example 16 has relatively poor stability, which may have some negative impact on the device performance of example 24;
3. it can be seen from comparative examples 2 and 8-14 that the performance of the organic electroluminescent device is better when the mass of the resonance type TADF material is 0.5-10% of the mass of the TTA material, and the performance of the organic electroluminescent device is more remarkably improved especially when the mass is 0.5-5%; when the mass of the resonance type TADF material is more than 10% of the mass of the TTA material, the performance of the organic electroluminescent device tends to decrease, but the performance is excellent as compared with the comparative example;
therefore, when the mass of the resonance type TADF material is 0.5 to 10% of the mass of the TTA material, the organic electroluminescent device is more excellent in roll-off, lifetime, and half-peak width;
4. as can be seen from comparison of examples 2 and 15 to 20, when the mass of the wide band gap material is 10 to 100% of that of the TTA material, the performance of the organic electroluminescent device is better, and particularly, when the mass is 10 to 50%, the performance of the organic electroluminescent device is more prominent; when the mass of the wide band gap material is more than 100% of that of the TTA material, the performance of the organic electroluminescent device tends to decrease, but the performance is excellent compared to the comparative example;
therefore, when the mass of the wide band gap material is 10-100% of that of the TTA material, the organic electroluminescent device is superior in roll-off, lifetime and half-peak width;
5. in examples 1, 4, 5, the device performance of example 1 was better than that of example 4, and the device performance of example 4 was better than that of example 5, probably because: the TTA materials in examples 1, 4, and 5 all contained 1N atom, but since the N atom of the TTA material in example 1 and the centroid of anthracene (3.78 angstroms) were closer, the SOC of the TTA material in example 1 was larger, and thus more excellent performance was exhibited; since the centroid distance (5.16 angstroms) of the N atom and anthracene of the TTA material in example 4 is smaller than the centroid distance (7.93 angstroms) of the N atom and anthracene of the TTA material in example 5, the device performance of example 4 is more excellent than that of example 5;
similarly, in examples 2, 3 and 6, the centroid distance between the N atom of the TTA material and anthracene in example 2 (3.77 angstroms), the centroid distance between the N atom of the TTA material and anthracene in example 3 (5.16 angstroms), and the centroid distance between the N atom of the TTA material and anthracene in example 6 (7.95 angstroms), therefore, the device performance of example 2 is better than that of example 3, and the device performance of example 3 is better than that of example 6;
6. in examples 1 and 2, the device performance of example 2 was superior to that of example 1, probably because: compared with example 1, the heteroatom is more in example 2, so that the SOC of the TTA material in example 2 is larger, and the TTA material shows more excellent performance;
also, example 3 is superior to example 4 in device performance due to more heteroatoms in the TTA material in example 3 relative to example 4;
7. from examples 21 and 22, it can be seen that when the heteroatoms are the same family atoms, the heteroatoms with larger atomic number are more beneficial to improve the device performance, probably because: atoms with larger atomic numbers enhance SOC more significantly because lone-pair electrons are closer to the central group.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (12)

1. An organic electroluminescent device comprising a light-emitting layer; the light-emitting layer includes a wide band gap material, a triplet-triplet annihilation material, and a resonance-type thermally activated delayed fluorescence material;
a first excited singlet energy level of the wide band gap material is greater than a first excited singlet energy level of the triplet-triplet annihilation material, which is greater than a first excited singlet energy level of the resonant thermally activated delayed fluorescence material; a first excited triplet energy level of the wide bandgap material is greater than a first excited triplet energy level of the triplet-triplet annihilation material and a first excited triplet energy level of the resonant thermally activated delayed fluorescence material, the first excited triplet energy level of the resonant thermally activated delayed fluorescence material being greater than the first excited triplet energy level of the triplet-triplet annihilation material;
wherein the spin-orbit coupling constant SOC of the n-th excited triplet state and the first excited singlet state of the triplet-triplet annihilation material meets the following requirement, n is more than or equal to 2 and less than or equal to 6:
SOC≥0.30cm -1 ；
the difference of energy levels of a first excited singlet state and a first excited triplet state of the resonance type thermal activation delayed fluorescence material is less than or equal to 0.5 ev.
2. The organic electroluminescent device according to claim 1, wherein the triplet-triplet annihilation material has the structure of formula 1,
Figure FDA0003787449080000011
in the formula 1, A is selected from anthryl, naphthyl, perylenyl, pyrenyl, fluorenyl, phenanthryl, fluoranthenyl, benzophenanthryl,
Figure FDA0003787449080000013
One of the group and acenaphthylene, X is independently selected from a group with heteroatom, and m is more than or equal to 1.
3. The organic electroluminescent device according to claim 2, wherein in formula 1, X is selected from substituted or unsubstituted C 3 -C 30 Heterocyclic group of (1), C substituted by functional substituent 6 -C 30 One of the aryl groups of (a);
the functional substituent is selected from C 3 -C 30 At least one of a heterocyclic group, a straight chain group containing a hetero atom, and a branched group containing a hetero atom.
4. The organic electroluminescent device according to claim 2 or 3, wherein in formula 1, X contains 1 to 10 hetero atoms.
5. The organic electroluminescent device according to claim 2 or 3, wherein in formula 1, the distance between at least one heteroatom in X and the centroid of A is 10 angstrom or less.
6. The organic electroluminescent device according to claim 4, wherein in formula 1, the distance between at least one heteroatom in X and the centroid of A is ≤ 10 angstroms.
7. The organic electroluminescent device according to claim 5, wherein in formula 1, the distance between at least one heteroatom in X and the centroid of A is less than or equal to 7 angstroms.
8. The organic electroluminescent device according to claim 6, wherein in formula 1, the distance between at least one heteroatom in X and the centroid of A is less than or equal to 7 angstroms.
9. The organic electroluminescent device according to any one of claims 1 to 3, wherein the triplet-triplet annihilation material is a compound having one of the structures shown below:
Figure FDA0003787449080000012
Figure FDA0003787449080000021
Figure FDA0003787449080000031
Figure FDA0003787449080000041
Figure FDA0003787449080000051
Figure FDA0003787449080000061
Figure FDA0003787449080000071
Figure FDA0003787449080000081
Figure FDA0003787449080000091
Figure FDA0003787449080000101
Figure FDA0003787449080000111
Figure FDA0003787449080000121
Figure FDA0003787449080000131
Figure FDA0003787449080000141
Figure FDA0003787449080000151
10. the organic electroluminescent device according to any one of claims 1 to 3 and 6 to 8, wherein the mass of the wide band gap material in the light-emitting layer is 10 to 200% of the mass of the triplet-triplet annihilation material, and the mass of the resonance-type thermally activated delayed fluorescence material is 0.5 to 30% of the mass of the triplet-triplet annihilation material.
11. The organic electroluminescent device according to any one of claims 1 to 3 and 6 to 8, wherein the thickness of the light-emitting layer is 5 to 100 nm.
12. A display device comprising the organic electroluminescent element as claimed in any one of claims 1 to 11.
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