CN113725377A

CN113725377A - Light emitting device, light emitting substrate, and light emitting apparatus

Info

Publication number: CN113725377A
Application number: CN202111013747.7A
Authority: CN
Inventors: 刘杨; 陈雪芹; 邱丽霞
Original assignee: BOE Technology Group Co Ltd
Current assignee: BOE Technology Group Co Ltd
Priority date: 2021-08-31
Filing date: 2021-08-31
Publication date: 2021-11-30
Anticipated expiration: 2041-08-31
Also published as: CN113725377B

Abstract

The invention relates to the technical field of illumination and display, in particular to a light-emitting device, a light-emitting substrate and a light-emitting device. The light emitting efficiency can be improved. A light emitting device comprising: a first electrode and a second electrode which are arranged in a stacked manner, and a light-emitting layer which is arranged between the first electrode and the second electrode; the material of the light-emitting layer comprises a host material and a guest material, the host material comprises a first host material and a second host material, the majority carrier of the first host material is a hole, and the majority carrier of the second host material is an electron; an absolute value of a difference between a HOMO level of the first host material and a HOMO level of the second host material is less than or equal to 0.4eV, and an absolute value of a difference between a LUMO level of the first host material and a LUMO level of the second host material is less than or equal to 0.4 eV; an absolute value of a difference between the HOMO level of the guest material and the HOMO level of the first host material is less than or equal to 0.4 eV; the absolute value of the difference between the LUMO level of the guest material and the LUMO level of the second host material is less than or equal to 0.4 eV.

Description

Light emitting device, light emitting substrate, and light emitting apparatus

Technical Field

The invention relates to the technical field of illumination and display, in particular to a light-emitting device, a light-emitting substrate and a light-emitting device.

Background

Organic Light Emitting Diodes (OLEDs) have the characteristics of self-luminescence, wide viewing angle, fast response time, high Light Emitting efficiency, low operating voltage, thin substrate thickness, capability of manufacturing large-sized and bendable substrates, and simple manufacturing process, and are known as the next generation of "star" display technology.

Disclosure of Invention

The invention mainly aims to provide a light-emitting device, a light-emitting substrate and a light-emitting device. The light emitting efficiency can be improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

in one aspect, an embodiment of the present invention provides a light emitting device, including: a first electrode and a second electrode which are arranged in a stacked manner, and a light-emitting layer which is arranged between the first electrode and the second electrode; the material of the light-emitting layer comprises a host material and a guest material, the host material comprises a first host material and a second host material, the polarity of a majority carrier in the first host material is opposite to that of a majority carrier in the second host material, and the majority carrier of the first host material is a hole; wherein an absolute value of a difference between a HOMO level of the first host material and a HOMO level of the second host material is less than or equal to 0.4eV, and an absolute value of a difference between a LUMO level of the first host material and a LUMO level of the second host material is less than or equal to 0.4 eV; an absolute value of a difference between the HOMO level of the guest material and the HOMO level of the first host material is less than or equal to 0.4 eV; an absolute value of a difference between a LUMO level of the guest material and a LUMO level of the second host material is less than or equal to 0.4 eV.

In some embodiments, there is an overlap region between the normalized emission spectrum of the first host material and the normalized absorption spectrum of the second host material; the integrated area of the overlap region is greater than or equal to 10% of the integrated area of the normalized emission spectrum of the first host material.

In some embodiments, the second host material is a TADF material.

In some embodiments, no exciplex is formed between the first host material and the second host material.

In some embodiments, the difference between the lowest singlet exciton energy of the first host material and the lowest singlet exciton energy of the second host material is greater than or equal to 0.1eV, and the difference between the lowest triplet exciton energy of the first host material and the lowest triplet exciton energy of the second host material is greater than or equal to 0.1 eV.

In some embodiments, the first host material has a lowest singlet exciton energy greater than or equal to 2.7eV less than or equal to 3.3eV, the second host material has a lowest singlet exciton energy greater than or equal to 2.3eV less than or equal to 2.8 eV; the first host material has a lowest triplet exciton energy greater than or equal to 2.5eV less than or equal to 3.1eV, and the second host material has a lowest triplet exciton energy greater than or equal to 2.2eV less than or equal to 2.7 eV.

In some embodiments, the guest material is a phosphorescent material; the difference between the lowest triplet exciton energy of the second host material and the lowest triplet exciton energy of the guest material is greater than or equal to 0.1 eV.

In some embodiments, the guest material has a lowest triplet exciton energy greater than or equal to 2.1eV and less than or equal to 2.6 eV.

In some embodiments, the first host material has a HOMO level greater than or equal to-5.6 eV less than or equal to-5.3 eV, and the second host material has a HOMO level greater than or equal to-5.8 eV less than or equal to-5.4 eV; the first host material has a LUMO level greater than or equal to-2.4 eV and less than or equal to-2.0 eV, and the second host material has a LUMO level greater than or equal to-2.6 eV and less than or equal to-2.2 eV.

In some embodiments, the guest material has a HOMO level greater than or equal to-5.5 eV and less than or equal to-5.0 eV and a LUMO level greater than or equal to-3.0 eV and less than or equal to-2.5 eV.

In some embodiments, the first host material is selected from any of the compounds represented by the following formula (I):

wherein R is₁、R₂、R₃And R₄Same or different, each independently selected from deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any one of the heteroaryl groups of (1), L₁And L₂Same or different, each independently selected from single bond, substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀Any one of the heteroarylenes of (a); ar (Ar)₁And Ar₂Same or different, each independently selected from substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a); at R₁、R₂、R₃、R₄、L₁、L₂And Ar₁And Ar₂Wherein the substituted substituent is selected from C₁～C₁₀Any of (a) alkyl groups.

In some embodiments, the second host material is selected from any one of the compounds represented by the following formulas (II-1) and (II-2):

wherein, X₁Is N, X₂Is selected from C (R)₅)₂、N(R₆)、O、S、C＝O、S＝O、P(R₇)₃P-O, Se and Si (R)₈)2 any one of, X₃、X₄And X₅The same or different, are respectively and independently selected from C (R)₉) Or N, and at least one is N; r₅、R₆、R₇、R₈、R₉、R₁₀And R₁₁Same or different, each independently selected from hydrogen, deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a); l is₃Selected from single bond, substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀Any one of the heteroarylenes of (a); at R₅、R₆、R₇、R₈、R₉、R₁₀、R₁₁And L₃Wherein the substituted substituent is selected from C₁～C₁₀Any of (a) alkyl groups.

In some embodiments, the difference between the decomposition temperature and the sublimation temperature of the first host material is greater than or equal to 20 ℃, the difference between the decomposition temperature and the sublimation temperature of the second host material is greater than or equal to 20 ℃, and the absolute value of the difference between the sublimation temperature of the first host material and the sublimation temperature of the second host material is less than or equal to 30 ℃.

In some embodiments, the mass ratio of the first host material to the second host material is 1:9 to 9: 1.

In some embodiments, the guest material is selected from any of the compounds represented by the following formula (III):

wherein, X₆Is selected from N (R)₁₅)、C(R₁₆)₂、O、S、C＝O、S＝O、P(R₁₇)₃、P＝O、Se、Si(R₁₈)₂Any one of (1), A₁～A₈The same or different, are respectively and independently selected from C (R)₁₉) Or N, and A₁～A₈At least one of which is N; r₁₂、R₁₃、R₁₄、R₁₅、R₁₆、R₁₇、R₁₈And R₁₉Same or different, each independently selected from hydrogen, deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl, substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a); at R₁₂、R₁₃、R₁₄、R₁₅、R₁₆、R₁₇、R₁₈And R₁₉Wherein the substituted substituent is selected from C₁～C₁₀Any one of alkyl groups of (a); n is 1 or 2.

In some embodiments, the guest material is present in the light-emitting layer in a mass proportion of 5% to 15%.

In some embodiments, further comprising: a hole blocking layer and an electron blocking layer; the difference between the lowest singlet exciton energy of the hole blocking layer and the lowest singlet exciton energy of the first host material is greater than or equal to 0.1 eV; the difference between the lowest triplet exciton energy of the hole blocking layer and the lowest triplet exciton energy of the first host material is greater than or equal to 0.1 eV; the difference between the lowest singlet exciton energy of the electron blocking layer and the lowest singlet exciton energy of the second host material is greater than or equal to 0.1 eV; the difference between the lowest triplet exciton energy of the electron blocking layer and the lowest triplet exciton energy of the second host material is greater than or equal to 0.1 eV.

In some embodiments, the material of the hole blocking layer is selected from any one of triazine compounds; the material of the electron blocking layer is any one of triphenylamine compounds.

In another aspect, there is provided a light emitting substrate including: a substrate; a plurality of light emitting devices disposed on the substrate; wherein at least one light emitting device is a light emitting device as described above.

In still another aspect, a light emitting device is provided, which includes the light emitting substrate as described above.

The embodiment of the invention provides a light-emitting device, a light-emitting substrate and a light-emitting device. By making the respective HOMO levels and LUMO levels of the first host material, the second host material, and the guest material satisfy the above-described relationship, the respective HOMO levels and LUMO levels of the first host material, the second host material, and the guest material can be matched, and compared with the energy levels of the HOMO levels and LUMO levels of the first host material, the second host material, and the guest material that are not collocated (matched), fewer holes and electrons are directly captured by the guest material, and sufficient transfer of energy from the host material to the guest material can be achieved, so that device efficiency can be improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a cross-sectional structural view of a light-emitting substrate according to an embodiment of the present invention;

fig. 2 is a top view structural diagram of a light-emitting substrate according to an embodiment of the present invention;

fig. 3 is a diagram illustrating a relationship between energy levels of layers in a light-emitting functional layer according to an embodiment of the present invention;

fig. 4 is a cross-sectional structural view of another light-emitting substrate according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. 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.

In the following, the terms "first", "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

Example embodiments are described herein with reference to cross-sectional and/or plan views as idealized example figures. In the drawings, the thickness of layers and regions are exaggerated for clarity. Variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, the exemplary embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an etched region shown as a rectangle will typically have curved features. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the exemplary embodiments.

Some embodiments of the present disclosure provide a light emitting device including a light emitting substrate, but may also include other components, such as a Circuit for providing an electrical signal to the light emitting substrate to drive the light emitting substrate to emit light, which may be referred to as a control Circuit, and a Circuit board and/or an IC (integrated Circuit) electrically connected to the light emitting substrate.

In some embodiments, the light emitting device may be a lighting device, in which case the light emitting device serves as a light source, performing a lighting function. For example, the light emitting device may be a backlight unit in a liquid crystal display device, a lamp for interior or exterior illumination, or various signal lamps, etc.

In other embodiments, the light emitting device may be a display device, in which case, the light emitting substrate is a display substrate for implementing an image (i.e., picture) display function. The light emitting device may comprise a display or a product comprising a display. The Display may be a Flat Panel Display (FPD), a micro Display, or the like. The display may be a transparent display or an opaque display, depending on whether the user can see the scene division at the back of the display. The display may be a flexible display or a normal display (which may be referred to as a rigid display) depending on whether the display can be bent or rolled. For example, a product containing a display may include: computer monitors, televisions, billboards, laser printers with display capability, telephones, cell phones, Personal Digital Assistants (PDAs), laptop computers, Digital cameras, camcorders, viewfinders, vehicles, large area walls, theater screens or stadium signs, and the like.

Some embodiments of the present invention provide a light emitting substrate 1, as shown in fig. 1 and 2, the light emitting substrate 1 including a substrate 11, a pixel defining layer 12 disposed on the substrate 11, and a plurality of light emitting devices 13. The pixel defining layer 12 has a plurality of openings Q, and a plurality of light emitting devices 13 may be disposed corresponding to the plurality of openings Q. The plurality of light emitting devices 13 here may be all or part of the light emitting devices 13 included in the light emitting substrate 1; the plurality of openings Q may be all or part of the openings on the pixel defining layer 12.

The substrate 11 may be a flexible substrate or a rigid substrate, and in the case where the substrate 11 is a flexible substrate, the material of the substrate 11 may be a PI (Polyimide) material. In the case where the substrate 11 is a rigid substrate, the substrate 11 may be glass. Here, the substrate 11 may be a substrate on which a pixel driver circuit has been formed.

The light-emitting substrate 1 may be a top-emission type light-emitting substrate (light emitted from the light-emitting device 13 is emitted from a side away from the substrate 11), a bottom-emission type light-emitting substrate (light emitted from the light-emitting device 13 is emitted from a side of the substrate 11), or a double-emission type light-emitting substrate.

As shown in fig. 1, for example, the light-emitting substrate 1 is a top-emission light-emitting substrate, and the light-emitting substrate 1 may further include: and a light extraction layer 14 disposed on a side of the light emitting device 13 away from the substrate 11. The light extraction layer 14 is configured to extract light emitted from each light emitting device 13.

Each of the light emitting devices 13 may include a first electrode 131, a second electrode 132, and a light emitting function layer 133 disposed between the first electrode 131 and the second electrode 132, the light emitting function layer 133 including a light emitting layer 133 a.

In some embodiments, as shown in fig. 1, the first electrode 131 can be an anode, and in this case, the second electrode 132 is a cathode. In other embodiments, as shown in fig. 2, the first electrode 131 can be a cathode, and in this case, the second electrode 132 is an anode.

In some embodiments, the material of the anode may be selected from a high work function material, such as ITO (Indium Tin Oxides), IZO (Indium Zinc Oxide), or a composite material (such as Ag/ITO, Al/ITO, Ag/IZO or Al/IZO, wherein "Ag/ITO" designates a stacked structure of a metallic silver electrode and an ITO electrode stack), and the material of the cathode may be selected from a low work function material, such as metallic Al, Ag or Mg, or a low work function metallic alloy material (such as magnesium aluminum alloy, magnesium silver alloy), and the like.

For an OLED light emitting device, the light emitting principle of the light emitting device 13 is: in a circuit in which an anode and a cathode are connected, holes are injected into the light-emitting layer 133a through the anode, electrons are injected into the light-emitting layer 133a through the cathode, the formed electrons and holes form excitons in the light-emitting layer 133a, and the excitons transition back to the ground state by radiation to emit photons.

As shown in fig. 1 and 2, in order to improve the efficiency of injecting electrons and holes into the light emitting layer 133a, the light emitting function layer 133 may further include: at least one of a Hole Injection Layer (HIL)133b, an Electron Injection Layer (EIL)133c, a Hole Transport Layer (HTL)133d, and an Electron Transport Layer (ETL)133 e. Illustratively, the light emitting function layer 133 may include a Hole Transport Layer (HTL)133d disposed between the anode and the light emitting layer 133a, and an Electron Transport Layer (ETL)133e disposed between the cathode and the light emitting layer 133 a. In order to further improve the efficiency of the electron and hole injection light emitting layer 133a, the light emitting function layer 133 may further include a Hole Injection Layer (HIL)133b disposed between the anode and the hole transport layer 133d, and an Electron Injection Layer (EIL)133c disposed between the cathode and the electron transport layer 133 e.

In some embodiments, the electron transport layer 133e may be selected from organic materials having good electron transport properties, and may also be doped with LiQ in the organic materials₃Li and Ca, and the like, and the thickness of the alloy is 10-70 nm. The hole transport layer 133d may be selected fromN, N ' -diphenyl-N, N ' - (1-naphthyl) -1,1 ' -biphenyl-4, 4 ' -diamine (N, N ' -Bis- (1-naphthyl) -N, N ' -Bis-phenyl- (1,1 ' -biphenyl) -4,4 ' -diamine) and 4,4 ' -cyclohexylbis [ N, N-Bis (4-methylphenyl) aniline](4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline]) Any one of the above.

In other embodiments, the material of the electron injection layer 133c may be selected from low work function metals, such as Li, Ca, Yb, and the like, or metal salts LiF, LiQ₃And the thickness can be 0.5 to 2 nm. The material of the hole injection layer 133b may be selected from CuPc (copper phthalocyanine), HATCN (2,3,6,7,10, 11-hexacyano-1, 4,5,8,9, 12-hexaazatriphenylene, hexaazatriphenylene hexacyano), MnO₃The material may be P-doped, and the thickness may be 5 to 30 nm.

The light-emitting substrate 1 may further include a driving circuit connected to each light-emitting device 13, and the driving circuit may be connected to the control circuit to drive each light-emitting device 13 to emit light according to an electrical signal input by the control circuit. The driving circuit may be an active driving circuit or a passive driving circuit.

The light emitting substrate 1 may emit white light, monochromatic light (light of a single color), light of adjustable color, or the like.

In a first example, the light emitting substrate 1 may emit white light. At this time, as shown in fig. 1, the plurality of light emitting devices 13 includes a light emitting device 13R emitting red light, a light emitting device 13G emitting green light, and a light emitting device 13B emitting blue light. At this time, by controlling the red light-emitting device 13R, the green light-emitting device 13G, and the blue light-emitting device 13B to emit light simultaneously, the mixing of the red light-emitting device 13R, the green light-emitting device 13G, and the blue light-emitting device 13B can be realized to make the light-emitting substrate 1 exhibit white light.

In this example, the light-emitting substrate 1 can be used for illumination, that is, can be applied to an illumination device.

In a second example, the light-emitting substrate 1 may emit monochromatic light. At this time, from among the plurality of light emitting devices 13, at least one light emitting device 13 is a light emitting device 13G emitting green light, it can be known that the light emitting substrate 1 can emit green light, that is, the plurality of light emitting devices 13 are all the light emitting devices 13G emitting green light. In this example, the light-emitting substrate 1 can be used for illumination, that is, can be applied to an illumination device, and can also be used for displaying an image or a screen of a single color, that is, can be applied to a display device.

In a third example, the light-emitting substrate 1 can emit light with adjustable color (i.e. color light), and the light-emitting substrate 1 is similar to the structure of the plurality of light-emitting devices 13 described in the first example, and the color and the brightness of the mixed light emitted by the light-emitting substrate 1 can be controlled by controlling the brightness of each light-emitting device 13, so as to realize color light emission.

In this example, the light-emitting substrate 1 can be used for displaying images or pictures, i.e., can be applied to a display device, and of course, the light-emitting substrate 1 can also be used in a lighting device.

In a third example, taking the light-emitting substrate 1 as a display substrate, such as a full-color display panel, as shown in fig. 2, the light-emitting substrate 1 includes a display area a and a peripheral area S disposed around the display area a. The display area a includes a plurality of sub-pixel regions P, each of the sub-pixel regions P corresponds to one opening, one opening corresponds to one light emitting device 13, and a pixel driving circuit 200 for driving the corresponding light emitting device to emit light is disposed in each of the sub-pixel regions P. The peripheral region S is used for wiring such as the gate driver circuit 100 connected to the pixel driver circuit 200.

Based on the above structure, some embodiments of the present disclosure provide a light emitting device, in which the material of the light emitting layer 133a in the light emitting device 13 includes a host material H and a guest material D (also referred to as a dopant material), that is, the material of the light emitting layer 133a is a material of a host-guest doping system. The host material H is a material capable of energy transfer with the guest material D, has good hole and electron transport capabilities, good thermal stability and film formation properties, and has a large proportion in the light-emitting layer 133 a. The guest material D occupies a small amount of the light-emitting layer 133 a.

For the host-guest doping system, there are two light emitting mechanisms of energy transfer from the host material H to the guest material D and formation of excitons directly on the guest material D.

Specifically, under the action of the applied electric field, electrons and holes are respectively injected into the light-emitting functional layer 133 from the cathode and the anode, and the specific process is as follows: as shown in fig. 3, electrons transition from the fermi level of the cathode to the LUMO (Lowest Unoccupied Molecular Orbital) level of the light-emitting functional layer, and holes transition from the fermi level of the anode to the HOMO (Highest Occupied Molecular Orbital) level of the light-emitting functional layer. Next, electrons are sequentially transported at the LUMO level of the electron injection layer 133c and the electron transport layer 133e and are finally injected into the light emitting layer 133a, holes are sequentially transported at the HOMO level of the hole injection layer 133b and the hole transport layer 133d, and transitions are injected into the light emitting layer 133 a. After the electrons and holes are injected into the light-emitting layer 133a, they are bound together by coulomb force on the same molecule or adjacent molecules, and thus electron-hole pairs, i.e., excitons, are formed. The excitons may be formed on the host material H first (in which case the electrons and holes are captured by the host material H first), or may be formed directly on the guest material D (in which case the electrons and holes are captured directly by the guest material D).

When excitons are first formed on the host material H, this system includes Foster energy transfer of the host material H to the guest material D, which can be achieved in a longer distance by means of coulomb effect of charges, and Dexter energy transfer, which requires overlapping of electron clouds and can be achieved only between adjacent molecules. The purpose of improving the luminous efficiency can be achieved by using a physical doping method and utilizing the effective energy transfer among materials. When excitons are directly formed on the guest material D, electrons and holes are directly recombined on the guest material D to emit light.

For the host-guest doped system, whether electrons and holes are captured by the host material H or directly captured by the guest material D first depends on the energy matching relationship between layers in the light-emitting functional layer 133, and one function of the host material H is to transport electrons and holes injected into the light-emitting layer 133a (i.e., the host material H may be a bipolar molecule (i.e., a molecule including a donor group and an acceptor group, which can simultaneously transport holes and electrons), or the host material H may be a dual host material including a p-type material (i.e., a hole-transporting material) and an n-type material (an electron-transporting material), so as to transport electrons and holes, so that the electrons and holes have a wider recombination region, and thus, the host-guest doped system is more prone to the light-emitting mechanism of energy transfer from the host material H to the guest material D, while the light emitting mechanism in which excitons are formed directly on the guest material D is not desired, the HOMO (Highest Occupied Molecular Orbital) level and the LUMO (Lowest Unoccupied Molecular Orbital) level of the material of the layer adjacent to the light emitting layer 133a in the light emitting functional layer 133 are made to match the HOMO level and the LUMO level of the host material D in the light emitting layer 133a, that is, taking the layers adjacent to the light emitting layer 133a in the light emitting functional layer as the electron transport layer 133e and the hole transport layer 133D as an example, the LUMO level of the material of the electron transport layer 133e is made to match the LUMO level of the host material D of the light emitting layer 133a, and the HOMO level of the material of the hole transport layer 133D is made to match the HOMO level of the host material H in the light emitting layer 133 a. At this time, illustratively, the difference between the LUMO level of the material of the electron transport layer 133e and the LUMO level of the host material H of the light emitting layer 133a is less than or equal to 0.5eV, so that electrons in the electron transport layer 133e can be injected onto the host material H of the light emitting layer 133a against the energy barrier (energy barrier of LUMO level) between the electron transport layer 133e and the host material of the light emitting layer 133a under a certain electric field, the difference between the HOMO level of the material of the hole transport layer 133d and the HOMO level of the host material H of the light emitting layer 133a can also be less than or equal to 0.5eV, holes in the hole transport layer 133d can be injected onto the host material H of the light emitting layer 133a under a certain electric field against an energy barrier (energy barrier of HOMO energy level) between the hole transport layer 133d and the host material H of the light emitting layer 133, so that electrons and holes are formed on the host material H first.

However, it is found through research that, in the case that the energy levels of the host and guest materials are not reasonably matched, a certain proportion of holes and electrons in the light-emitting layer 133a are directly captured by the guest material D, so that the number of effective carriers (the number of carriers that can be used for energy transfer to achieve light emission) in the light-emitting layer 133a is reduced, and the light-emitting efficiency is reduced.

In addition, for a dual host system, it is more advantageous to design materials suitable for electron transport and hole transport than the host materials of the ambipolar molecules, and thus, in some embodiments, host material H includes first host material H1 and second host material H2. The majority carriers in the first host material H1 and the majority carriers in the second host material H2 are of opposite polarity, and the majority carriers of the first host material H1 are holes.

That is, the first host material H1 and the second host material H2 may be a p-type material and an n-type material, respectively, and as for the semiconductor material, there are two types of carriers, that is, holes and electrons, generally present in the material, and the semiconductor material may be divided into a p-type material and an n-type material according to whether the hole proportion in the material is more than the electron proportion, the majority of the holes in the p-type material being holes, which may also be referred to as majority carriers, and the holes being electrons, which may also be referred to as minority carriers, and the electrons being electrons, which may also be referred to as majority carriers, in the n-type material.

Based on the above, it is important how to reasonably match the energy levels among the first host material H1, the second host material H2, and the guest material D, so as to achieve sufficient energy transfer from the host material H to the guest material D, and further improve the efficiency of the light emitting device 13.

In some embodiments of the present disclosure, the absolute value of the difference between the HOMO level of the first host material H1 and the HOMO level of the second host material H2 is less than or equal to 0.4eV, and the absolute value of the difference between the LUMO level of the first host material H1 and the LUMO level of the second host material H2 is less than or equal to 0.4 eV. An absolute value of a difference between the HOMO level of the guest material D and the HOMO level of the first host material H1 is less than or equal to 0.4 eV; the absolute value of the difference between the LUMO level of the guest material D and the LUMO level of the second host material H2 is less than or equal to 0.4 eV.

That is, in the embodiments of the present disclosure, the relationship between the energy level of the first host material H1, the energy level of the second host material H2, and the energy level of the guest material D is as follows:

∣HOMO_H1-HOMO_H2∣≤0.4eV；

∣LUMO_H1-LUMO_H2∣≤0.4eV；

∣HOMO_H1-HOMO_D∣≤0.4eV；

∣LUMO_H2-LUMO_D∣≤0.4eV。

wherein, the HOMO_H1Denotes the HOMO energy level, HOMO, of the first host material H1_H2Denotes the HOMO energy level, LUMO, of the second host material H2_H1Denotes the LUMO energy level, LUMO, of the first host material H1_H2Denotes the LUMO energy level, HOMO, of the second host material H1_DRepresents the HOMO level, LUMO, of guest material D_DRepresenting the LUMO energy level of guest material D.

The HOMO level and the LUMO level of each of the first host material H1, the second host material H2, and the guest material D, and the emission color of the guest material D are not particularly limited as long as the HOMO level and the LUMO level of each of the first host material H1, the second host material H2, and the guest material D satisfy the above-described relationship in one host-guest doping system.

Experiments show that by enabling the HOMO levels and the LUMO levels of the first host material H1, the second host material H2, and the guest material D to satisfy the above-mentioned relationship, the HOMO levels and the LUMO levels of the first host material H1, the second host material H2, and the guest material D can be matched, and compared with the energy levels of the HOMO levels and the LUMO levels of the first host material H1, the second host material H2, and the guest material D, fewer holes and electrons are directly captured by the guest material D, and energy sufficient transfer from the host material H to the guest material D can be realized, so that device efficiency can be improved.

The mechanism for realizing the luminescence of the guest material D by the energy transfer from the host material H to the guest material D is as follows: under photoexcitation or electroluminescence, holes and electrons form excitons on the host material H, and the excitons are transferred from the host material H to the guest material D by energy transfer from the host material H to the guest material D, and then emit light by radiative transition of the guest material D.

It was found through research that Foster energy transfer is dominant in the photoluminescence process, while the luminescence performance of the device is affected by Dexter energy transfer and charge trapping (i.e., charge trap trapping, i.e., electrons and holes are formed directly on the guest material D) in the electroluminescence process.

Specifically, in the photoluminescence process, under the irradiation of incident light, the host material H absorbs photons to generate excitons, the excitons transfer energy to the guest material D through Foster energy transfer, so that the excitons are excited and form excitons on the guest material D, and the excitons are de-excited to emit radiation. Dexter energy transfer is the energy transfer process completed while directly transferring electrons or holes in an excited state to other molecules in a ground state to form new excitons, and it transfers energy by direct exchange of carriers.

In the above energy transfer process, there are mainly three possible energy transfer paths, and the first, first host material H1 and second host material H2 transfer exciton energy formed on the respective materials to guest material D, respectively. Second, the first host material H1 and the second host material H2 form an exciplex, and exciton energy formed on the exciplex is transferred to the guest material D. Third, one of the first host material H1 and the second host material H2 transfers exciton energy formed thereon to the other (e.g., the first host material H1 transfers exciton energy formed thereon to the second host material H2), excites the other (the second host material H2) to form excitons, and then transfers exciton energy formed thereon to the guest material D through the other (the second host material H2).

Wherein, the energy transmission paths can exist in the energy transmission process at the same time, or only any two of the energy transmission paths exist in combination or one of the energy transmission paths in the whole energy transmission process.

In some embodiments, there is an overlap region between the normalized emission spectrum of the first host material H1 and the normalized absorption spectrum of the second host material H2, the integrated area of the overlap region being greater than or equal to 10% of the integrated area of the normalized emission spectrum of the first host material H1.

The emission spectrum of the first host material H1 is a photoluminescence emission spectrum emitted when the first host material is made into a sheet and excited by light having a wavelength of 320 nm.

The absorption spectrum of the second host material H2 is a spectrum that can be absorbed by the second host material H2 when irradiated with light (including ultraviolet light and visible light) of 200 to 800nm wavelength band, and the spectrum reflects the absorbance (as ordinate) of the second host material H2 to light of different wavelengths (as abscissa) when irradiated with light of 200 to 800nm wavelength band.

The spectrum normalization is a normalization process of normalizing the spectrum, that is, setting the total intensity of the photoluminescence emission spectrum of the first host material H1 to one and the total absorbance of the absorption spectrum of the second host material H2 to one, so that both the fluorescence intensity and the absorbance of the absorption spectrum on the ordinate of the photoluminescence emission spectrum become decimal. Thus, the emission spectrum of the first host material H1 and the absorption spectrum of the second host material H2 show spectra in the same coordinate system, which are the normalized emission spectrum of the first host material H1 and the normalized absorption spectrum of the second host material H2.

Since the first host material H1 has an overlapping region between the normalized emission spectrum and the normalized absorption spectrum of the second host material H2, and the area of the overlapping region is large, effective Foster energy transfer can occur between the first host material H1 and the second host material H2, and the energy transfer efficiency is improved.

In some embodiments, the second host material H2 is a TADF (Thermally Activated Delayed Fluorescence) material. The TADF material is a material having a small energy gap between a singlet excited state and a triplet excited state, and in this material, sufficient reverse intersystem crossing from the triplet excited state to the singlet excited state can be generated by thermal excitation, so that triplet excitons can be converted into singlet excitons.

Specifically, in the TADF material, the probability of radiative recombination of singlet excitons is much less than the probability of intersystem crossing, i.e., most of the singlet excitons become triplet excitons through intersystem crossing, and the triplet excitons formed directly in addition to the triplet excitons cannot be radiatively recombined due to spin forbidden; subsequently, the triplet excitons are changed to singlet excitons by reverse intersystem crossing after thermal excitation. This complex process allows for a substantial extension of exciton lifetime, with eventual radiative deactivation of singlet excitons to produce delayed fluorescence.

In some embodiments, where efficient Foster energy transfer occurs between the first and second host materials H1 and H2, the difference between the lowest singlet exciton energy S1 of the first host material H1 and the lowest singlet exciton energy S1 of the second host material H2 is greater than or equal to 0.1eV, and the difference between the lowest triplet exciton energy T1 of the first host material H1 and the lowest triplet exciton energy T1 of the second host material H2 is greater than or equal to 0.1 eV.

In these embodiments, by making the first host material H1 have the lowest singlet exciton energy S1 and the lowest triplet exciton energy T1 higher than the second host material H2, reverse transfer of energy from the second host material H2 to the first host material H1 can be effectively avoided, while by making the difference between the lowest triplet exciton energy T3 of the first host material H1 and the lowest triplet exciton energy T1 of the second host material H2 be 0.1eV or more, the triplet excitons can also be confined on the second host material H2, and in the case where the second host material is a TADF material, the second host material H2 can convert the triplet excitons into the singlet excitons through reverse intersystem crossing, so that the effective utilization of the triplet excitons can be achieved. In addition, for the guest material D being a phosphorescent material, the triplet exciton energy is mainly utilized for the light emission of the guest material, and thus, in some embodiments, the singlet exciton energy of the first host material H1 and the singlet exciton energy of the second host material H2 are not limited as long as the difference between the lowest triplet exciton energy T1 of the first host material and the lowest triplet exciton energy T1 of the second host material H2 satisfies the above condition.

In some embodiments, the lowest singlet exciton energy S1 of the first host material H1 is greater than or equal to 2.7eV less than or equal to 3.3eV and the lowest singlet exciton energy S1 of the second host material H2 is greater than or equal to 2.3eV less than or equal to 2.8 eV. The first host material H1 has a lowest triplet exciton energy T1 of greater than or equal to 2.5eV less than or equal to 3.1eV and the second host material H2 has a lowest triplet exciton energy T1 of greater than or equal to 2.2eV less than or equal to 2.7 eV.

In some embodiments, the guest material D is a phosphorescent material, and the difference between the lowest triplet exciton energy T1 of the second host material H2 and the lowest triplet exciton energy T1 of the guest material D is greater than or equal to 0.1 eV.

In these embodiments, since the guest material D is a phosphorescent material, by making the second host material H2 have the lowest triplet exciton energy T1 higher than that of the guest material D, energy can be effectively prevented from being reversely transferred from the guest material D to the second host material H2, and triplet excitons can be confined on the guest material D, so that the guest material D can realize light emission by making full use of the energy of the triplet excitons.

In order to realize the ideal Foster energy transfer from the host material H to the guest material D, the energy levels of the host material H and the guest material D are required to be matched, and the spectral characteristics of the host material H and the guest material D are reflected in that the emission spectrum of the host material H and the absorption spectrum of the guest material D are well overlapped. Taking the third energy transfer approach as an example, the normalized emission spectrum of the second host material H2 has a larger overlap with the normalized absorption spectrum of the guest material D. The explanation of the normalized emission spectrum of the second host material H2 and the normalized absorption spectrum of the guest material D and the correlation therebetween can be referred to the explanation and explanation of the normalized emission spectrum of the first host material H1 and the normalized absorption spectrum of the second host material H2, which are not described herein again.

In some embodiments, no exciplex is formed between the first host material H1 and the second host material H2. The exciplex is an aggregate of two molecules or atoms of different species, the two molecules or atoms have strong action in an excited state, a new energy level is generated, an emission spectrum is different from that of a single species, and no fine structure exists.

In these embodiments, since no exciplex is formed between the first host material H1 and the second host material H2, the first host material H1 and the second host material H2 do not generate spectra different from their intrinsic spectra, so that the change of the light emitting properties of the first host material H1 and the second host material H2 can be avoided, and the color purity of the light emitted by the final guest material D can be improved.

Here, the above-described first host material H1 and second host material H2 may be mixed in any ratio as long as the first host material H1 and second host material H2 can form Foster energy transfer.

In some embodiments, the mass ratio of the first host material H1 to the second host material H2 is 1:9 to 9: 1.

In some embodiments, the HOMO level of the first host material H1 is greater than or equal to-5.6 eV and less than or equal to-5.3 eV, and the HOMO level of the second host material H2 is greater than or equal to-5.8 eV and less than or equal to-5.4 eV. That is, -5.6eV less than or equal to HOMO_H1≤-5.3eV，-5.8eV≤HOMO_H2≤-5.4eV。

Specifically, the HOMO level of the first host material H1 may be-5.6 eV, -5.5eV, -5.4eV, or-5.3 eV, the HOMO level of the second host material H2 may be-5.8 eV, -5.7eV, -5.6eV, or-5.4 eV, and since the absolute value of the difference between the HOMO level of the first host material H1 and the HOMO level of the second host material H2 is less than or equal to 0.4eV, the HOMO level of the second host material H2 may be any of-5.8 eV to-5.4 eV in the case where the HOMO level of the first host material H1 is-5.6 eV, the HOMO level of the second host material H2 may be any of-5.8 eV to-5.4 eV, the HOMO level of the first host material H1 is-5.5 eV, the HOMO level of the second host material H2 may be any of-5.8 eV to-5.4 eV, and the HOMO level of the second host material H358 eV may be any of-5.8 eV to-5.8 eV, when the HOMO level of the material H1 is-5.3 eV, the HOMO level of the second host material H2 may be any value from-5.7 eV to-5.4 eV.

In these embodiments, the first host material H1 and the second host material H2 may be selected from materials having HOMO energy levels in the above-described range, that is, the first host material H1 and the second host material H2 may be green host materials.

In some embodiments, the LUMO level of the first host material H1 is greater than or equal to-2.4 eV and less than or equal to-2.0 eV and the LUMO level of the second host material H2 is greater than or equal to-2.6 eV and less than or equal to-2.2 eV. That is, -2.4eV less than or equal to the LUMO_H1≤-2.0eV，-2.6eV≤LUMO_H2≤-2.2eV。

Specifically, the LUMO level of the first host material H1 may be-2.4 eV, -2.3eV, -2.2eV, -2.1eV, or-2.0 eV, the LUMO level of the second host material H2 may be-2.6 eV, -2.5eV, -2.4eV, -2.3eV, or-2.2 eV, and since the absolute value of the difference between the LUMO level of the first host material H1 and the LUMO level of the second host material H2 is less than or equal to 0.4eV, in the case where the LUMO level of the first host material H1 is-2.4 eV, the LUMO level of the second host material H2 may be any of-2.6 eV to-2.2 eV, and in the case where the LUMO level of the first host material H1 is-2.3 eV, the LUMO level of the second host material H2 may be any of-2.6 eV to-2.2 eV, and in the case where the LUMO level of the first host material H1 is-2.78 eV, the LUMO level of the second host material H2 may be any of-2.6 eV to-2.2 eV, the LUMO level of the second host material H2 may be any of-2.5 eV to-2.2 eV in the case where the LUMO level of the first host material H1 is-2.1 eV, and the LUMO level of the second host material H2 may be any of-2.1 eV to-2.2 eV in the case where the LUMO level of the first host material H1 is-2.0 eV.

In these embodiments, the first host material H1 and the second host material H2 may be selected from materials having LUMO energy levels within the above-described range, that is, the first host material H1 and the second host material H2 may be green host materials.

It was found through experiments that by defining the HOMO level and the LUMO level of the first host material H1, and the HOMO level and the LUMO level of the second host material H2 in the above ranges, and by controlling the absolute value of the difference between the HOMO level of the first host material H1 and the HOMO level of the second host material H2 to be less than or equal to 0.4eV, and the absolute value of the difference between the LUMO level of the first host material H1 and the LUMO level of the second host material H2 to be less than or equal to 0.4eV, in the case where Foster energy transfer occurs between the first host material H1 and the second host material H2, the PLQY (Photoluminescence Quantum Yield) of the host material H can be increased to the maximum extent.

The photoluminescence quantum yield can be used for characterizing the luminous efficiency of a sample, namely measuring the efficiency of the sample for effectively utilizing absorbed light, and can be mathematically expressed as the ratio of the number of emitted photons to the number of absorbed photons, which is the ratio of the number of emitted photons to the number of absorbed photons of the second host material H2 during Foster energy transfer of the first host material H1 and the second host material H2.

In other embodiments, guest material D has a HOMO level greater than or equal to-5.5 eV and less than or equal to-5.0 eV and a LUMO level greater than or equal to-3.0 eV and less than or equal to-2.5 eV. That is, -5.5eV ≦ HOMO_D≤-5.0eV，-3.0eV≤LUMO_D≤-2.5eV。

In these embodiments, the guest material D may be a green light emitting material. It was found through experiments that in the case where the HOMO level of the first host material H1 is greater than or equal to-5.6 eV and less than or equal to-5.3 eV, the LUMO level of the first host material H1 is greater than or equal to-2.4 eV and less than or equal to-2.0 eV, the HOMO level of the second host material H2 is greater than or equal to-5.8 eV and less than or equal to-5.4 eV, and the LUMO level of the second host material H2 is greater than or equal to-2.6 eV and less than or equal to-2.2 eV, the PLQY of the guest material D can be maximally increased by defining the HOMO level and the LUMO level of the guest material D within the above ranges.

PLQY of guest material D herein has the same meaning as PLQY of second host material H2 described above, and specific reference may be made to the above description.

Note that, since the absolute value of the difference between the HOMO level of the guest material D and the HOMO level of the first host material H1 is less than or equal to 0.4eV, the absolute value of the difference between the LUMO level of the guest material D and the LUMO level of the second host material H2 is less than or equal to 0.4 eV; accordingly, in the case where the HOMO level of the first host material H1 is-5.6 eV, the HOMO level of the guest material D may be any of-5.5 eV to-5.2 eV, in the case where the HOMO level of the first host material H1 is-5.5 eV, the HOMO level of the guest material D may be any of-5.5 eV to-5.1 eV, in the case where the HOMO level of the first host material H1 is-5.4 eV, the HOMO level of the guest material D may be any of-5.5 eV to-5.0 eV, and in the case where the HOMO level of the first host material H1 is-5.3 eV, the HOMO level of the guest material D may be any of-5.5 eV to-5.0 eV. In the case where the LUMO level of the second host material H2 is-2.6 eV, the LUMO level of the guest material D may be any value from-3.0 eV to-2.5 eV, in the case where the LUMO level of the second host material H2 is-2.5 eV, the LUMO level of the guest material D may be any value from-2.9 eV to-2.5 eV, in the case where the LUMO level of the second host material H2 is-2.4 eV, the LUMO level of the guest material D may be any value from-2.8 eV to-2.5 eV, in the case where the LUMO level of the second host material H2 is-2.3 eV, the LUMO level of the guest material D may be any value from-2.7 eV to-2.5 eV, in the case where the LUMO level of the second host material H2 is-2.2 eV, the LUMO level of the guest material D may be any value from-2.6 eV to-2.5 eV.

In some embodiments, the guest material is present in the light-emitting layer in a mass fraction of 5% to 15%. By limiting the mass ratio of the guest material D within the above range, a long life can be ensured while ensuring high efficiency.

In some embodiments, the first host material H1 is selected from any one of the compounds shown below in formula (I):

wherein R is₁、R₂、R₃And R₄Same or different, each independently selected from deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any one of the heteroaryl groups of (1), L₁And L₂Are the same or different and are each independently selected from the group consisting of single bond, substituted orUnsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀Any one of the heteroarylenes of (a); ar (Ar)₁And Ar₂Same or different, each independently selected from substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a); at R₁、R₂、R₃、R₄、L₁、L₂And Ar₁And Ar₂Wherein the substituted substituent is selected from C₁～C₁₀Any of (a) alkyl groups.

Wherein, in R₁、R₂、R₃And R₄In the case of deuterium, the formula represents that each benzene ring corresponding to two carbazoles has one hydrogen substituted by deuterium, and the structural formula can be shown as the following formula, wherein R is₁Deuterium as such may be attached to carbon number 1, 2,3 or 4, R₂May be attached to carbon 5, 6,7 or 8, R₃May be attached to

carbon number

9, 10,11 or 12, R₄May be attached to

carbon number

13, 14, 15 or 16.

With R₃And R₄All are benzene rings as examples, and the structural formula is shown as the following formula, wherein R₁May be attached to carbon number 1, 2,3 or 4, R₂May be attached to carbon 5, 6,7 or 8, R₃May be attached to

carbon number

9, 10,11 or 12, R₄May be attached to

carbon number

13, 14, 15 or 16.

At L₁And L₂Selected from single bonds, the structural formula can be shown as the following formula, namely two carbazolyl groups are respectively reacted with Ar₁And Ar₂Are directly connected.

At L₁And L₂Selected from substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀In the case of any of the heteroarylenes of (1), L₁And L₂May be both phenylene in which case Ar₁May be located at the ortho, meta or para position of the carbazole, Ar, on the phenylene group to which it is attached₂May be located in the ortho, meta or para position of the carbazole in the phenylene group to which it is attached. The specific structural formula is shown as follows.

Or, L₁And L₂May each have a plurality of benzene rings, e.g., a condensed ring, biphenyl, etc., and L is₁And L₂Heterocyclic rings such as carbazole, dibenzofuran, and the like may also be used. Exemplified by L₁And L₂For example, the condensed ring of formula (I) can be represented by the following formula (I) _1, wherein L₁And L₂For biphenyl as an example, formula (I) can be represented by the following formula (I) _2, with L₁And L₂For carbazole, the formula (I) may be represented by the following formula (I) _ 3.

In the same way, Ar₁And Ar₂May have L as described above₁And L₂The structures listed are identical except that Ar₁And Ar₂At the end of the molecule, at L₁And L₂In the case of arylene, Ar₁And Ar₂Is aryl at L₁And L₂In the case of a heteroarylene group, Ar₁And Ar₂Is heteroaryl.

In addition, in R₁、R₂、R₃、R₄、L₁、L₂And Ar₁And Ar₂Wherein the substituted substituent is C₁～C₁₀Alkyl of (2) means that, at R₁、R₂、R₃、R₄、L₁、L₂And Ar₁And Ar₂In the case of being selected from substituted alkyl, aryl or heteroaryl, the substituted substituent may be methyl, ethyl, t-butyl, etc.

Exemplified by R₁、R₂、R₃、R₄And Ar₁And Ar₂Are each selected from substituted phenyl, L₁And L₂Are each selected from substituted phenylene radicals, R₁、R₂、R₃、R₄And Ar₁And Ar₂Wherein the substituted substituent is t-butyl, L₁And L₂The substituent(s) substituted in (1) is, for example, methyl, and the formula (I) can be represented by the following formula. Wherein, the number of each substituent can be one or more, and each substituent can be positioned at ortho-position, para-position or meta-position of the benzene ring.

Above only shows R₁、R₂、R₃、R₄And Ar₁And Ar₂Wherein the substituents are the same, L₁And L₂In the same manner as in the case of the substituted substituent, it can be understood by those skilled in the art that R is₁、R₂、R₃、R₄And Ar₁And Ar₂Wherein the substituents may be different, L₁And L₂The substituents in (1) may also be different.

It is to be noted that the connection relationship between the two carbazolyl groups in the formula (I) may be represented by any one of the following formulae.

In some embodiments, Ar₁And Ar₂Each independently selected from any one of substituted or unsubstituted dibenzofuran, dibenzothiophene and dibenzopyrrole.

In these embodiments, by introducing an electron-donating group such as dibenzofuran to N of carbazole, the HOMO level of the molecule and the triplet exciton energy T1 can be increased, so that the HOMO barrier when the hole transport layer transfers holes to P-type can be reduced, which is more favorable for holes to jump to the first host material H1, and by increasing the triplet exciton energy T1, exciton reverse transfer (for example, from the second host material H2 to the first host material H1) can be prevented, so that efficiency reduction due to exciton quenching can be avoided.

In some embodiments, the second host material H2 is selected from any one of the compounds represented by the following formulas (II-1) and (II-2):

wherein, X₁Is N, X₂Is selected from C (R)₅)₂、N(R₆)、O、S、C＝O、S＝O、P(R₇)₃P-O, Se and Si (R)₈)₂Any one of (1), X₃、X₄And X₅The same or different, are respectively and independently selected from C (R)₉) Or N, and at least one is N; r₅、R₆、R₇、R₈、R₉、R₁₀And R₁₁Same or different, each independently selected from hydrogen, deuterium, substituted or unsubstituted_C1～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a); l is₃Selected from single bond, substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀Any one of the heteroarylenes of (a); at R₅、R₆、R₇、R₈、R₉、R₁₀、R₁₁And L₃Wherein the substituted substituent is selected from C₁～C₁₀Any of (a) alkyl groups.

Wherein, the formula (II-1) can be written as the following structures:

the formula (II-2) can be written as the following structures:

wherein, C is substituted or unsubstituted₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀For heteroaryl groups, reference may be made to the above description of alkyl, aryl and heteroaryl groups of formula (I), which are not further described herein.

At L₃Selected from single bonds, represents a benzo five-membered ring (including indene, indole, benzofuran/thiophene) carbazole directly linked to the azine.

At L₃Selected from substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀In the case of any of the heteroarylenes of (a), the description of arylene and heteroarylene may also refer to the description of arylene and heteroarylene in formula (I) above, and will not be repeated here.

In addition, for R here₅、R₆、R₇、R₈、R₉、R₁₀、R₁₁And L₃The description of the substituted substituents in (1) may also be referred to the above for R₁、R₂、R₃、R₄、L₁、L₂To do so byAnd Ar₁And Ar₂The description of the substituted substituents in (1) is also omitted herein for brevity.

In some embodiments, L₃Selected from single bonds. Namely, the benzo five-membered ring carbazole is directly connected with azine, the structure can increase the molecular distortion degree, and the physical property shows that the energy gap delta Est of the singlet excited state and the triplet excited state of the molecule can be further reduced, so that the triplet exciton energy can be more fully utilized.

In some embodiments, the difference between the decomposition temperature Td and the sublimation temperature Ts of the first host material H1 is greater than or equal to 20 ℃, the difference between the decomposition temperature Td and the sublimation temperature Ts of the second host material H2 is greater than or equal to 20 ℃, and the absolute value of the difference between the sublimation temperature Ts of the first host material H1 and the sublimation temperature Ts of the second host material H2 is less than or equal to 30 ℃.

Evaporation is a method of obtaining a thin film material by heating the material in a vacuum environment, vaporizing the material, and depositing the vaporized material on a substrate (herein referred to as a substrate).

In an actual manufacturing process, for a light emitting layer including the first host material H1, the second host material H2, and the guest material D, the first host material H1 and the second host material H2 are mixed and then evaporated together, the sublimation temperatures Ts of the first host material H1 and the second host material H2 determine the evaporation temperature, and if the sublimation temperatures of the first host material H1 and the second host material H2 are greatly different, the problem of uneven evaporation occurs. In these embodiments, by selecting the first host material H1 and the second host material H2 having a small difference in sublimation temperature, the problem of uneven evaporation can be avoided, and at the same time, since the difference between the decomposition temperature Td of the first host material H1 and the sublimation temperature Ts is greater than or equal to 20 ℃, and the difference between the decomposition temperature Td of the second host material H2 and the sublimation temperature Ts is greater than or equal to 20 ℃, during evaporation, it is also possible to prevent decomposition of one of the first host material H1 and the second host material H2 due to an excessively low decomposition temperature Td, and improve the evaporation stability.

In some embodiments, the sublimation temperature Ts of the first host material H1 and the sublimation temperature Ts of the second host material H2 are both 120 ℃ to 250 ℃, and the decomposition temperature Td of the first host material H1 and the decomposition temperature Td of the second host material H2 are both 270 ℃ to 360 ℃.

In some embodiments, the absolute value of the difference between the glass transition temperature Tg of the first host material H1 and the glass transition temperature Tg of the second host material H2 is less than or equal to 30 ℃, and the glass transition temperature Tg of the first host material H1 is between 80 ℃ and 160 ℃.

In these embodiments, by selecting the first host material H1 having a glass transition temperature Tg of 80 to 160 ℃ and controlling the absolute value of the difference between the glass transition temperatures Tg of the first host material H1 and the second host material H2 to be in the range of 30 ℃, it is possible to make the first host material H1 and the second host material H2 have higher glass transition temperatures Tg, and as the glass transition temperature Tg is higher, the film formed by evaporation is more uniform and the stability is better.

In some embodiments, guest material D is selected from any of the compounds represented by formula (III) below:

wherein, X₆Is selected from N (R)₁₅)、C(R₁₆)₂、O、S、C＝O、S＝O、P(R₁₇)₃、P＝O、Se、Si(R₁₈)₂Any one of (1), A₁～A₈The same or different, are respectively and independently selected from C (R)₁₉) Or N, and A₁～A₈At least one of which is N; r₁₂、R₁₃、R₁₄、R₁₅、R₁₆、R₁₇、R₁₈And R₁₉Same or different, each independently selected from hydrogen, deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl, substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a); at R₁₂、R₁₃、R₁₄、R₁₅、R₁₆、R₁₇、R₁₈And R₁₉Wherein the substituted substituent is selected from C₁～C₁₀Alkyl groups of (a); n is 1 or 2.

Wherein, C is substituted or unsubstituted₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀For heteroaryl groups, see above for formula

(I) The description of the alkyl, aryl and heteroaryl groups in (A) is not repeated here.

In addition, for R here₁₂、R₁₃、R₁₄、R₁₅、R₁₆、R₁₇、R₁₈And R₁₉The description of the substituted substituents in (1) may also be referred to the above for R₁、R₂、R₃、R₄、L₁、L₂And Ar₁And Ar₂The description of the substituted substituents in (1) is also omitted herein for brevity.

In these embodiments, the guest material D with such a structure has a high PLQY, and the aza-dibenzofuran/thiophene bipyridine belongs to a partially rigid group, and its introduction can reduce molecular deformation and vibration amplitude of molecules of the guest material from a ground state to an excited state, thereby reducing a half-peak width of a spectrum, improving color purity of a green device, and further improving a color gamut.

In addition, experiments show that the guest material D provided by the invention is low in evaporation temperature, does not cause molecular cracking after long-time evaporation, and improves the stability of the evaporation process. Moreover, by introducing the aza-dibenzofuran/thiophene bipyridyl group, the HOMO level of the guest material D can be increased (i.e., the HOMO level of the guest material D is made shallower), and compared with the HOMO level of the guest material D in the related art, the HOMO level of the guest material D is deeper, so that holes and electrons are easily formed in the guest material D, and trapping of electrons and holes can be avoided, thereby increasing energy transfer efficiency and further increasing light emitting efficiency.

In some embodiments, as shown in fig. 4, the light emitting device 13 further includes a hole blocking layer 133f and an electron blocking layer 133 g. The difference between the lowest singlet exciton energy S1 of the hole blocking layer 133f and the lowest singlet exciton energy S1 of the first host material H1 is greater than or equal to 0.1 eV; the difference between the lowest triplet exciton energy T1 of the hole blocking layer 133f and the lowest triplet exciton energy T1 of the first host material H1 is greater than or equal to 0.1 eV; the difference between the lowest singlet exciton energy S1 of the electron blocking layer 133g and the lowest singlet exciton energy S1 of the second host material H2 is greater than or equal to 0.1 eV; the difference between the lowest triplet exciton energy T1 of the electron blocking layer 133g and the lowest triplet exciton energy T1 of the second host material H2 is greater than or equal to 0.1 eV.

In these embodiments, both the triplet excitons and the singlet excitons can be confined in the light-emitting layer 133a, thereby avoiding the problem that the excitons in the light-emitting layer 133a leak out of the light-emitting layer 133a to lower the exciton utilization rate, which is disadvantageous for the improvement of the light-emitting efficiency.

In some embodiments, the absolute value of the difference between the LUMO level of the second host material H2 and the LUMO level of the electron blocking layer 133g is greater than or equal to 0.5eV, and the absolute value of the difference between the HOMO level of the hole blocking layer 133f and the HOMO level of the first host material H1 is greater than or equal to 0.5 eV.

In these embodiments, by defining the LUMO level of the electron blocking layer 133g and the HOMO level of the hole blocking layer 133f, the electron blocking layer 133g may more conveniently transport holes to block electrons, and the hole blocking layer 133f may more conveniently transport electrons to block holes, so that excitons of the light emitting layer may be prevented from leaking out of the light emitting layer to cause exciton quenching, and efficiency may be reduced.

In some embodiments, the material of the hole blocking layer is selected from any one of triazine compounds; the material of the electron blocking layer 133g is selected from any one of triphenylamine-based compounds.

For example, the material of the hole blocking layer may be selected from any one of the following structural formulas:

as another example, the material of the electron blocking layer may be selected from any one of the following structural formulas:

in order to objectively evaluate the technical effects of the embodiments of the present disclosure, hereinafter, the technical solutions provided by the present disclosure will be exemplarily described in detail through the following experimental examples and comparative examples.

In the following experimental examples and comparative examples, the device structure and the test conditions of the device were the same, wherein the structure of the light emitting device is represented as: anode (ITO)/hole injection layer (material)/hole transport layer (material)/electron blocking layer (material)/light emitting layer (first host material: second host material (mass ratio 1: 1): guest material (10%))/hole blocking layer (material)/electron transport layer (material)/electron injection layer (material)/cathode (magnesium/silver).

Wherein the first host material: second host material (1: 1): the guest material (10%) means that the mass ratio of the first host material to the second host material is 1: 1, the mass ratio of the guest material in the light-emitting layer is 10%. Magnesium/silver refers to a mixed material of magnesium and silver.

Except that the first host material H1, the second host material H2, and the guest material D used in the comparative example and the experimental example were not completely the same. In experimental example 1, the structure of the first host material is shown as P1 below, the structure of the second host material is shown as N1 below, and the structure of the guest material is shown as D1 below; in experimental example 2, the structure of the first host material is shown as P2 below, the structure of the second host material is shown as N2 below, and the structure of the guest material is shown as D2 below, in comparative example 1, the structure of the first host material is shown as P1 below, the structure of the second host material is shown as N1 below, and the structure of the guest material is shown as D3 below, in comparative example 2, the structure of the first host material is shown as P2 below, the structure of the second host material is shown as N3 below, and the structure of the guest material is shown as D2 below.

The physical properties of the first host material, the second host material, and the guest material used in comparative examples 1 to 2 and experimental examples 1 to 2 are shown in table 1 below.

TABLE 1

Name of Material	HOMO/eV	LUMO/eV	T1/eV	Tg/℃	Ts/℃	Td/℃
							P1	-5.42	-2.12	2.66	86	131	311
P2	-5.46	-2.13	2.68	89	135	306
							P3	-5.43	-2.09	2.61	90	138	314
N1	-5.51	-2.36	2.52	88	128	302
							N2	-5.54	-2.31	2.54	90	132	308
N3	-5.83	-2.54	2.50	91	144	312
							D1	-5.10	-2.71	2.42	120	262	411
D2	-5.12	-2.69	2.39	122	258	406
							D3	-5.20	-2.98	2.52	144	296	421

Based on the above materials, the first host material, the second host material, and the guest material used in comparative examples 1 to 2 and experimental examples 1 to 2 were formed into a thin film, and PLQY was measured by the integrating sphere method, and the measurement results are shown in table 2 below.

TABLE 2

Group name	PLQY	Excited state lifetime τ/μ s
			Experimental example 1	0.89	1.8
Experimental example 2	0.87	1.7
			Comparative example 1	0.72	2.1
Comparative example 2	0.81	1.9

Combining tables 1 and 2, it can be seen that: by controlling the absolute value of the difference between the HOMO level of the guest material and the HOMO level of the first host material to be in the range of less than 0.4eV and the absolute value of the difference between the LUMO level of the guest material and the LUMO level of the second host material to be in the range of less than 0.4eV in experimental examples 1 and 2, as compared to comparative example 1 in which the absolute value of the difference between the HOMO level of the guest material and the HOMO level of the first host material is greater than 0.4eV and the absolute value of the difference between the LUMO level of the guest material and the LUMO level of the second host material is greater than 0.4eV, the PLQY of the light emitting layer can be increased, and thus the light emitting efficiency can be improved.

Therefore, the energy levels of the first host material, the second host material and the guest material are reasonably matched, so that the PLQY of the whole light-emitting device can be improved, and the light-emitting efficiency is improved. And tests on the excited state lifetime show that the luminous efficiency can be improved to the maximum extent under the condition that the excited state lifetime is between 1.7 and 1.8 mu s.

In addition, IVL (current-voltage-luminance) and life test data of the light emitting devices of experimental examples 1 to 2 and comparative examples 1 to 2 are shown in table 3 below.

TABLE 3

Group of	V(V)	Cd/A	CIEx	CIEy	LT95(h)
						Experimental example 1	89％	126％	0.25	0.72	132％
Experimental example 2	92％	121％	0.25	0.72	125％
						Comparative example 1	100％	100％	0.25	0.72	100％
Comparative example 2	102％	104％	0.25	0.72	105％

As can be seen from table 3, the test data in comparative example 1 is used as a reference, and the voltage, efficiency and lifetime data are all set to be 100%, the voltage, efficiency and lifetime of comparative example 2 are all improved compared with those of comparative example 1, while the voltage of experimental example 1 and that of experimental example 2 are both reduced to a certain extent, and the efficiency and lifetime are obviously improved compared with those of comparative example 1 and experimental example 2. While the color coordinates of comparative example 1, comparative example 2, experimental example 1 and experimental example 2 are all (0.25, 0.72), it can be known that comparative example 1, comparative example 2, experimental example 1 and experimental example 2 all have high color purity.

Therefore, the light-emitting efficiency of the light-emitting device can be improved, the voltage can be reduced, the service life can be prolonged, and the light-emitting device has a good application prospect by reasonably matching the energy levels of the first host material, the second host material and the guest material.

The IVL (Current-Voltage-Brightness) data are obtained by IVL equipment test, namely at a current density of 15mA/cm²In the case of the above data, CIEx and CIEy respectively represent the horizontal and vertical coordinates of the color coordinates, one color for each set of color coordinates, which can also be measured in an IVL device,the lifetime is tested in a dedicated lifetime device at a fixed current density (e.g., 15 mA/cm)²) The device is lit up and the time taken for the luminance of the light emitting device to decrease to 95% of the initial luminance is the lifetime of the device.

The scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of changes or substitutions within the technical scope of the present invention, and the present invention is intended to be covered thereby. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A light emitting device, comprising:

a first electrode and a second electrode which are arranged in a stacked manner;

a light-emitting layer provided between the first electrode and the second electrode;

the material of the light-emitting layer comprises a host material and a guest material, the host material comprises a first host material and a second host material, the polarity of a majority carrier in the first host material is opposite to that of a majority carrier in the second host material, and the majority carrier of the first host material is a hole;

wherein an absolute value of a difference between a HOMO level of the first host material and a HOMO level of the second host material is less than or equal to 0.4eV, and an absolute value of a difference between a LUMO level of the first host material and a LUMO level of the second host material is less than or equal to 0.4 eV;

an absolute value of a difference between the HOMO level of the guest material and the HOMO level of the first host material is less than or equal to 0.4 eV; an absolute value of a difference between a LUMO level of the guest material and a LUMO level of the second host material is less than or equal to 0.4 eV.

2. The light-emitting device according to claim 1,

the normalized emission spectrum of the first host material and the normalized absorption spectrum of the second host material have an overlap region therebetween;

the integrated area of the overlap region is greater than or equal to 10% of the integrated area of the normalized emission spectrum of the first host material.

3. The light-emitting device according to claim 1,

the second host material is a TADF material.

4. The light-emitting device according to claim 1,

no exciplex is formed between the first host material and the second host material.

5. The light-emitting device according to claim 1,

the difference between the lowest singlet exciton energy of the first host material and the lowest singlet exciton energy of the second host material is greater than or equal to 0.1eV, and the difference between the lowest triplet exciton energy of the first host material and the lowest triplet exciton energy of the second host material is greater than or equal to 0.1 eV.

6. The light-emitting device according to claim 5,

the first host material has a lowest singlet exciton energy greater than or equal to 2.7eV less than or equal to 3.3eV, and the second host material has a lowest singlet exciton energy greater than or equal to 2.3eV less than or equal to 2.8 eV;

the first host material has a lowest triplet exciton energy greater than or equal to 2.5eV less than or equal to 3.1eV, and the second host material has a lowest triplet exciton energy greater than or equal to 2.2eV less than or equal to 2.7 eV.

7. The light-emitting device according to claim 1,

the guest material is a phosphorescent material;

the difference between the lowest triplet exciton energy of the second host material and the lowest triplet exciton energy of the guest material is greater than or equal to 0.1 eV.

8. The light-emitting device according to claim 7,

the guest material has a lowest triplet exciton energy greater than or equal to 2.1eV and less than or equal to 2.6 eV.

9. The light-emitting device according to claim 1,

the HOMO level of the first host material is greater than or equal to-5.6 eV and less than or equal to-5.3 eV, and the HOMO level of the second host material is greater than or equal to-5.8 eV and less than or equal to-5.4 eV;

the first host material has a LUMO level greater than or equal to-2.4 eV and less than or equal to-2.0 eV, and the second host material has a LUMO level greater than or equal to-2.6 eV and less than or equal to-2.2 eV.

10. The light-emitting device according to claim 1,

the guest material has a HOMO level greater than or equal to-5.5 eV and less than or equal to-5.0 eV, and a LUMO level greater than or equal to-3.0 eV and less than or equal to-2.5 eV.

11. The light-emitting device according to any one of claims 1 to 10,

the first host material is selected from any one of compounds represented by the following formula (I):

wherein R is₁、R₂、R₃And R₄Same or different, each independently selected from deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any one of the heteroaryl groups of (1), L₁And L₂Same or different, each independently selected from single bond, substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀Any one of the heteroarylenes of (a); ar (Ar)₁And Ar₂Same or different, each independently selected from substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a);

at R₁、R₂、R₃、R₄、L₁、L₂And Ar₁And Ar₂Wherein the substituted substituent is selected from C₁～C₁₀Any of (a) alkyl groups.

12. The light-emitting device according to any one of claims 1 to 10,

the second host material is selected from any one of compounds represented by the following formulas (II-1) and (II-2):

wherein, X₁Is N, X₂Is selected from C (R)₅)₂、N(R₆)、O、S、C＝O、S＝O、P(R₇)₃P-O, Se and Si (R)₈)₂Any one of (1), X₃、X₄And X₅The same or different, are respectively and independently selected from C (R)₉) Or N, and at least one is N;

R₅、R₆、R₇、R₈、R₉、R₁₀and R₁₁Same or different, each independently selected from hydrogen, deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl and substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a);

L₃selected from single bond, substituted or unsubstituted C₆～C₃₀Arylene group and substituted or unsubstituted C₂～C₃₀Any one of the heteroarylenes of (a);

at R₅、R₆、R₇、R₈、R₉、R₁₀、R₁₁And L₃Wherein the substituted substituent is selected from C₁～C₁₀Any of (a) alkyl groups.

13. The light-emitting device according to any one of claims 1 to 10,

the difference between the decomposition temperature and the sublimation temperature of the first main body material is greater than or equal to 20 ℃, the difference between the decomposition temperature and the sublimation temperature of the second main body material is greater than or equal to 20 ℃, and the absolute value of the difference between the sublimation temperature of the first main body material and the sublimation temperature of the second main body material is less than or equal to 30 ℃.

14. The light-emitting device according to any one of claims 1 to 10,

the mass ratio of the first main body material to the second main body material is 1: 9-9: 1.

15. The light-emitting device according to any one of claims 1 to 10,

the guest material is selected from any one of compounds represented by the following formula (III):

wherein, X₆Is selected from N (R)₁₅)、C(R₁₆)₂、O、S、C＝O、S＝O、P(R₁₇)₃、P＝O、Se、Si(R₁₈)₂Any one of (1), A₁～A₈The same or different, are respectively and independently selected from C (R)₁₉) Or N, and A₁～A₈At least one of which is N;

R₁₂、R₁₃、R₁₄、R1₅、R₁₆、R₁₇、R₁₈and R₁₉Same or different, each independently selected from hydrogen, deuterium, substituted or unsubstituted C₁～C₁₀Alkyl, substituted or unsubstituted C₆～C₃₀Aryl, substituted or unsubstituted C₂～C₃₀Any of the heteroaryl groups of (a);

at R₁₂、R₁₃、R₁₄、R₁₅、R₁₆、R₁₇、R₁₈And R₁₉Wherein the substituted substituent is selected from C₁～C₁₀Any one of alkyl groups of (a);

n is 1 or 2.

16. The light-emitting device according to any one of claims 1 to 10,

the mass ratio of the guest material in the light-emitting layer is 5% to 15%.

17. The light-emitting device according to any one of claims 1 to 10, further comprising: a hole blocking layer and an electron blocking layer;

the difference between the lowest singlet exciton energy of the hole blocking layer and the lowest singlet exciton energy of the first host material is greater than or equal to 0.1 eV;

the difference between the lowest triplet exciton energy of the hole blocking layer and the lowest triplet exciton energy of the first host material is greater than or equal to 0.1 eV;

the difference between the lowest singlet exciton energy of the electron blocking layer and the lowest singlet exciton energy of the second host material is greater than or equal to 0.1 eV;

the difference between the lowest triplet exciton energy of the electron blocking layer and the lowest triplet exciton energy of the second host material is greater than or equal to 0.1 eV.

18. The light-emitting device according to claim 17,

the material of the hole blocking layer is selected from any one of triazine compounds;

the material of the electron blocking layer is any one of triphenylamine compounds.

19. A light-emitting substrate, comprising:

a substrate;

a plurality of light emitting devices disposed on the substrate;

wherein at least one light emitting device is a light emitting device as claimed in any one of claims 1 to 18.

20. A light-emitting device comprising the light-emitting substrate according to claim 19.