Patent Publication Number: US-2022231232-A1

Title: Organic electroluminescent device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to Chinese Patent Application No. CN 202011596467.9 filed on Dec. 30, 2020, and Chinese Patent Application No. CN 202111402521.6 filed on Nov. 24, 2021, the disclosure of which are incorporated herein by reference in their entireties. 
     TECHNICAL FIELD 
     The present disclosure relates to organic electronic devices, for example, organic electroluminescent devices. More particularly, the present disclosure relates to an electroluminescent device comprising a first compound having a structure of Formula 1 and a second compound having a structure of Formula 2, a display assembly comprising the electroluminescent device and a compound composition comprising the first compound and the second compound. 
     BACKGROUND 
     Organic electronic devices include, but are not limited to, the following types: organic light-emitting diodes (OLEDs), organic field-effect transistors (O-FETs), organic light-emitting transistors (OLETs), organic photovoltaic devices (OPVs), dye-sensitized solar cells (DSSCs), organic optical detectors, organic photoreceptors, organic field-quench devices (OFQDs), light-emitting electrochemical cells (LECs), organic laser diodes and organic plasmon emitting devices. 
     In 1987, Tang and Van Slyke of Eastman Kodak reported a bilayer organic electroluminescent device, which comprises an arylamine hole transporting layer and a tris-8-hydroxyquinolato-aluminum layer as the electron and emitting layer (Applied Physics Letters, 1987, 51 (12): 913-915). Once a bias is applied to the device, green light was emitted from the device. This device laid the foundation for the development of modern organic light-emitting diodes (OLEDs). State-of-the-art OLEDs may comprise multiple layers such as charge injection and transporting layers, charge and exciton blocking layers, and one or multiple emissive layers between the cathode and anode. Since the OLED is a self-emitting solid state device, it offers tremendous potential for display and lighting applications. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on flexible substrates. 
     The OLED can be categorized as three different types according to its emitting mechanism. The OLED invented by Tang and van Slyke is a fluorescent OLED. It only utilizes singlet emission. The triplets generated in the device are wasted through nonradiative decay channels. Therefore, the internal quantum efficiency (IQE) of the fluorescent OLED is only 25%. This limitation hindered the commercialization of OLED. In 1997, Forrest and Thompson reported phosphorescent OLED, which uses triplet emission from heavy metal containing complexes as the emitter. As a result, both singlet and triplets can be harvested, achieving 100% IQE. The discovery and development of phosphorescent OLED contributed directly to the commercialization of active-matrix OLED (AMOLED) due to its high efficiency. Recently, Adachi achieved high efficiency through thermally activated delayed fluorescence (TADF) of organic compounds. These emitters have small singlet-triplet gap that makes the transition from triplet back to singlet possible. In the TADF device, the triplet excitons can go through reverse intersystem crossing to generate singlet excitons, resulting in high IQE. 
     OLEDs can also be classified as small molecule and polymer OLEDs according to the forms of the materials used. A small molecule refers to any organic or organometallic material that is not a polymer. The molecular weight of the small molecule can be large as long as it has well defined structure. Dendrimers with well-defined structures are considered as small molecules. Polymer OLEDs include conjugated polymers and non-conjugated polymers with pendant emitting groups. Small molecule OLED can become the polymer OLED if post polymerization occurred during the fabrication process. 
     There are various methods for OLED fabrication. Small molecule OLEDs are generally fabricated by vacuum thermal evaporation. Polymer OLEDs are fabricated by solution process such as spin-coating, inkjet printing, and slit printing. If the material can be dissolved or dispersed in a solvent, the small molecule OLED can also be produced by solution process. 
     The emitting color of the OLED can be achieved by emitter structural design. An OLED may comprise one emitting layer or a plurality of emitting layers to achieve desired spectrum. In the case of green, yellow, and red OLEDs, phosphorescent emitters have successfully reached commercialization. Blue phosphorescent device still suffers from non-saturated blue color, short device lifetime, and high operating voltage. Commercial full-color OLED displays normally adopt a hybrid strategy, using fluorescent blue and phosphorescent yellow, or red and green. At present, efficiency roll-off of phosphorescent OLEDs at high brightness remains a problem. In addition, it is desirable to have more saturated emitting color, higher efficiency, and longer device lifetime. 
     KR20150077220A discloses a compound having the following general structure: 
     
       
         
         
             
             
         
       
     
     and further discloses a use of the compound in an organic electroluminescent device. However, the use of the compound and a compound having a structure of triazine bonded to dibenzofuran(thiophene) through a single bond or an arylene group as co-host materials is not disclosed or taught, and there is no teaching that a dual-host device containing the compound can achieve a better effect. 
     US20180337340A1 discloses a compound having the following general structure: 
     
       
         
         
             
             
         
       
     
     and further discloses an organic electroluminescent device containing the compound as a first host compound, where the organic electroluminescent device may further contain a second host compound. However, the use of the compound and the second host compound having a structure of triazine bonded to dibenzofuran(thiophene) through a single bond or an arylene group as co-host materials is not disclosed, and there is no teaching that a dual-host device containing the compound can improve device performance. 
     US2014312338A1 discloses a compound having the following general structure: 
     
       
         
         
             
             
         
       
     
     where A contains the following structure: 
     
       
         
         
             
             
         
       
     
     and B contains the following structure: 
     
       
         
         
             
             
         
       
     
     US2014312338A1 further discloses a use of the compound as a hole blocking material or an electron transporting material. However, neither does it disclose or teach the use of the compound as a host material, nor does it disclose or teach the use of the compound with another compound as co-host materials in an organic electroluminescent device. 
     US2015171340A1 discloses a compound having the following general structure: 
     
       
         
         
             
             
         
       
     
     and further discloses the use of the compound as a host material in an organic electroluminescent device. However, it does not disclose or teach the use of the compound with another compound as co-host materials in the organic electroluminescent device. 
     However, multiple host materials reported so far can still be improved. To meet the increasing requirements of the industry, it is an efficient research and development means to select a combination of suitable host materials and a new material combination still needs to be further researched and developed. 
     SUMMARY 
     The present disclosure provides an electroluminescent device comprising a first compound having a structure of Formula 1 and a second compound having a structure of Formula 2 to solve at least part of the above problems. 
     According to an embodiment of the present disclosure, disclosed is an electroluminescent device comprising an anode, a cathode, and an organic layer disposed between the anode and the cathode, wherein the organic layer comprises at least a first compound and a second compound; 
     wherein the first compound has a structure of H-L-Ar, wherein H has a structure represented by Formula 1: 
     
       
         
         
             
             
         
       
     
     wherein in Formula 1, 
     A 1 , A 2  and A 3  are, at each occurrence identically or differently, selected from N or CR, and the ring A, the ring B and the ring C are, at each occurrence identically or differently, selected from a carbocyclic ring having 5 to 18 carbon atoms or a heterocyclic ring having 3 to 18 carbon atoms; 
     R x  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
     Ar is selected from substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted arylamino having 3 to 30 carbon atoms or a combination thereof; 
     L is selected from a single bond, substituted or unsubstituted arylene having 6 to 30 carbon atoms, substituted or unsubstituted heteroarylene having 3 to 30 carbon atoms or a combination thereof; 
     R and R x  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
     adjacent substituents R, R x  can be optionally joined to form a ring; and 
     “*” represents a position where H is joined to L; 
     wherein the second compound has a structure represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     wherein in Formula 2, 
     Z is selected from O or S; 
     Z 1  to Z 8  are selected from C, N or CR z , and one of Z 1  to Z 4  is C and joined to L 3 ; 
     Ar 1  and Ar 2  are, at each occurrence identically or differently, selected from substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms or a combination thereof; 
     L 1  and L 2  are, at each occurrence identically or differently, selected from a single bond, substituted or unsubstituted arylene having 6 to 30 carbon atoms, substituted or unsubstituted heteroarylene having 3 to 30 carbon atoms or a combination thereof; 
     L 3  is selected from a single bond or substituted or unsubstituted arylene having 6 to 30 carbon atoms; 
     R z  is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
     adjacent substituents R z  can be optionally joined to form a ring. 
     According to an embodiment of the present disclosure, further disclosed is a compound composition comprising the first compound and the second compound in the preceding embodiment. 
     According to an embodiment of the present disclosure, further disclosed is a display assembly comprising the electroluminescent device in the preceding embodiment. 
     The present disclosure provides the electroluminescent device comprising the first compound having the structure of Formula 1 and the second compound having the structure of Formula 2. The electroluminescent device can significantly improve device efficiency and extend a lifetime and reduce device voltage to some extent, improving the overall performance of the device and having a broad commercial development prospect and application value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of an organic light-emitting device disclosed herein. 
         FIG. 2  is a schematic diagram of another organic light-emitting device disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     OLEDs can be fabricated on various types of substrates such as glass, plastic, and metal foil.  FIG. 1  schematically shows an organic light emitting device  100  without limitation. The figures are not necessarily drawn to scale. Some of the layers in the figures can also be omitted as needed. Device  100  may include a substrate  101 , an anode  110 , a hole injection layer  120 , a hole transport layer  130 , an electron blocking layer  140 , an emissive layer  150 , a hole blocking layer  160 , an electron transport layer  170 , an electron injection layer  180  and a cathode  190 . Device  100  may be fabricated by depositing the layers described in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, the contents of which are incorporated by reference herein in its entirety. 
     More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference herein in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference herein in its entirety. Examples of host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference herein in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference herein in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference herein in their entireties, disclose examples of cathodes including composite cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers are described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference herein in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference herein in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference herein in its entirety. 
     The layered structure described above is provided by way of non-limiting examples. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely. It may also include other layers not specifically described. Within each layer, a single material or a mixture of multiple materials can be used to achieve optimum performance. Any functional layer may include several sublayers. For example, the emissive layer may have two layers of different emitting materials to achieve desired emission spectrum. 
     In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer or multiple layers. 
     An OLED can be encapsulated by a barrier layer.  FIG. 2  schematically shows an organic light emitting device  200  without limitation.  FIG. 2  differs from  FIG. 1  in that the organic light emitting device include a barrier layer  102 , which is above the cathode  190 , to protect it from harmful species from the environment such as moisture and oxygen. Any material that can provide the barrier function can be used as the barrier layer such as glass or organic-inorganic hybrid layers. The barrier layer should be placed directly or indirectly outside of the OLED device. Multilayer thin film encapsulation was described in U.S. Pat. No. 7,968,146, which is incorporated by reference herein in its entirety. 
     Devices fabricated in accordance with embodiments of the present disclosure can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. Some examples of such consumer products include flat panel displays, monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, smart phones, tablets, phablets, wearable devices, smart watches, laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles displays, and vehicle tail lights. 
     The materials and structures described herein may be used in other organic electronic devices listed above. 
     As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from the substrate. There may be other layers between the first and second layers, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between. 
     As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form. 
     A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand. 
     It is believed that the internal quantum efficiency (IQE) of fluorescent OLEDs can exceed the 25% spin statistics limit through delayed fluorescence. As used herein, there are two types of delayed fluorescence, i.e. P-type delayed fluorescence and E-type delayed fluorescence. P-type delayed fluorescence is generated from triplet-triplet annihilation (TTA). 
     On the other hand, E-type delayed fluorescence does not rely on the collision of two triplets, but rather on the transition between the triplet states and the singlet excited states. 
     Compounds that are capable of generating E-type delayed fluorescence are required to have very small singlet-triplet gaps to convert between energy states. Thermal energy can activate the transition from the triplet state back to the singlet state. This type of delayed fluorescence is also known as thermally activated delayed fluorescence (TADF). A distinctive feature of TADF is that the delayed component increases as temperature rises. If the reverse intersystem crossing (RISC) rate is fast enough to minimize the non-radiative decay from the triplet state, the fraction of back populated singlet excited states can potentially reach 75%. The total singlet fraction can be 100%, far exceeding 25% of the spin statistics limit for electrically generated excitons. 
     E-type delayed fluorescence characteristics can be found in an exciplex system or in a single compound. Without being bound by theory, it is believed that E-type delayed fluorescence requires the luminescent material to have a small singlet-triplet energy gap (ΔE S-T ). Organic, non-metal containing, donor-acceptor luminescent materials may be able to achieve this. The emission in these materials is generally characterized as a donor-acceptor charge-transfer (CT) type emission. The spatial separation of the HOMO and LUMO in these donor-acceptor type compounds generally results in small AEs-T. These states may involve CT states. Generally, donor-acceptor luminescent materials are constructed by connecting an electron donor moiety such as amino- or carbazole-derivatives and an electron acceptor moiety such as N-containing six-membered aromatic rings. 
     Definition of Terms of Substituents 
     Halogen or halide—as used herein includes fluorine, chlorine, bromine, and iodine. 
     Alkyl—as used herein includes both straight and branched chain alkyl groups. Alkyl may be alkyl having 1 to 20 carbon atoms, preferably alkyl having 1 to 12 carbon atoms, and more preferably alkyl having 1 to 6 carbon atoms. Examples of alkyl groups include a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, an s-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, a neopentyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 1-pentylhexyl group, a 1-butylpentyl group, a 1-heptyloctyl group, and a 3-methylpentyl group. Of the above, preferred are a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, an s-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, a neopentyl group, and an n-hexyl group. Additionally, the alkyl group may be optionally substituted. 
     Cycloalkyl—as used herein includes cyclic alkyl groups. The cycloalkyl groups may be those having 3 to 20 ring carbon atoms, preferably those having 4 to 10 carbon atoms. Examples of cycloalkyl include cyclobutyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, 4,4-dimethylcylcohexyl, 1-adamantyl, 2-adamantyl, 1-norbornyl, 2-norbornyl, and the like. Of the above, preferred are cyclopentyl, cyclohexyl, 4-methylcyclohexyl, and 4,4-dimethylcylcohexyl. Additionally, the cycloalkyl group may be optionally substituted. 
     Heteroalkyl—as used herein, includes a group formed by replacing one or more carbons in an alkyl chain with a hetero-atom(s) selected from the group consisting of a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a phosphorus atom, a silicon atom, a germanium atom, and a boron atom. Heteroalkyl may be those having 1 to 20 carbon atoms, preferably those having 1 to 10 carbon atoms, and more preferably those having 1 to 6 carbon atoms. Examples of heteroalkyl include methoxymethyl, ethoxymethyl, ethoxyethyl, methylthiomethyl, ethylthiomethyl, ethylthioethyl, methoxymethoxymethyl, ethoxymethoxymethyl, ethoxyethoxyethyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, mercaptomethyl, mercaptoethyl, mercaptopropyl, aminomethyl, aminoethyl, aminopropyl, dimethylaminomethyl, trimethylsilyl, dimethylethylsilyl, dimethylisopropylsilyl, t-butyldimethylsilyl, triethylsilyl, triisopropylsilyl, trimethylsilylmethyl, trimethylsilylethyl, and trimethylsilylisopropyl. Additionally, the heteroalkyl group may be optionally substituted. 
     Alkenyl—as used herein includes straight chain, branched chain, and cyclic alkene groups. Alkenyl may be those having 2 to 20 carbon atoms, preferably those having 2 to 10 carbon atoms. Examples of alkenyl include vinyl, 1-propenyl group, 1-butenyl, 2-butenyl, 3-butenyl, 1,3-butandienyl, 1-methylvinyl, styryl, 2,2-diphenylvinyl, 1,2-diphenylvinyl, 1-methylallyl, 1,1-dimethylallyl, 2-methylallyl, 1-phenylallyl, 2-phenylallyl, 3-phenylallyl, 3,3-diphenylallyl, 1,2-dimethylallyl, 1-phenyl-1-butenyl, 3-phenyl-1-butenyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, cycloheptenyl, cycloheptatrienyl, cyclooctenyl, cyclooctatetraenyl, and norbornenyl. Additionally, the alkenyl group may be optionally substituted. 
     Alkynyl—as used herein includes straight chain alkynyl groups. Alkynyl may be those having 2 to 20 carbon atoms, preferably those having 2 to 10 carbon atoms. Examples of alkynyl groups include ethynyl, propynyl, propargyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3,3-dimethyl-1-butynyl, 3-ethyl-3-methyl-1-pentynyl, 3,3-diisopropyl-1-pentynyl, phenylethynyl, phenylpropynyl, etc. Of the above, preferred are ethynyl, propynyl, propargyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, and phenylethynyl. Additionally, the alkynyl group may be optionally substituted. 
     Aryl or an aromatic group—as used herein includes non-condensed and condensed systems. Aryl may be those having 6 to 30 carbon atoms, preferably those having 6 to 20 carbon atoms, and more preferably those having 6 to 12 carbon atoms. Examples of aryl groups include phenyl, biphenyl, terphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl, biphenyl, terphenyl, triphenylene, fluorene, and naphthalene. Examples of non-condensed aryl groups include phenyl, biphenyl-2-yl, biphenyl-3-yl, biphenyl-4-yl, p-terphenyl-4-yl, p-terphenyl-3-yl, p-terphenyl-2-yl, m-terphenyl-4-yl, m-terphenyl-3-yl, m-terphenyl-2-yl, o-tolyl, m-tolyl, p-tolyl, p-(2-phenylpropyl)phenyl, 4′-methylbiphenylyl, 4″-t-butyl-p-terphenyl-4-yl, o-cumenyl, m-cumenyl, p-cumenyl, 2,3-xylyl, 3,4-xylyl, 2,5-xylyl, mesityl, and m-quarterphenyl. Additionally, the aryl group may be optionally substituted. 
     Heterocyclic groups or heterocycle—as used herein include non-aromatic cyclic groups. Non-aromatic heterocyclic groups includes saturated heterocyclic groups having 3 to 20 ring atoms and unsaturated non-aromatic heterocyclic groups having 3 to 20 ring atoms, where at least one ring atom is selected from the group consisting of a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a silicon atom, a phosphorus atom, a germanium atom, and a boron atom. Preferred non-aromatic heterocyclic groups are those having 3 to 7 ring atoms, each of which includes at least one hetero-atom such as nitrogen, oxygen, silicon, or sulfur. Examples of non-aromatic heterocyclic groups include oxiranyl, oxetanyl, tetrahydrofuranyl, tetrahydropyranyl, dioxolanyl, dioxanyl, aziridinyl, dihydropyrrolyl, tetrahydropyrrolyl, piperidinyl, oxazolidinyl, morpholinyl, piperazinyl, oxepinyl, thiepinyl, azepinyl, and tetrahydrosilolyl. Additionally, the heterocyclic group may be optionally substituted. 
     Heteroaryl—as used herein, includes non-condensed and condensed hetero-aromatic groups having 1 to 5 hetero-atoms, where at least one hetero-atom is selected from the group consisting of a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a silicon atom, a phosphorus atom, a germanium atom, and a boron atom. A hetero-aromatic group is also referred to as heteroaryl. Heteroaryl may be those having 3 to 30 carbon atoms, preferably those having 3 to 20 carbon atoms, and more preferably those having 3 to 12 carbon atoms. Suitable heteroaryl groups include dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridoindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine, preferably dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, triazine, benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogs thereof. Additionally, the heteroaryl group may be optionally substituted. 
     Alkoxy—as used herein, is represented by —O-alkyl, —O-cycloalkyl, —O-heteroalkyl, or —O-heterocyclic group. Examples and preferred examples of alkyl, cycloalkyl, heteroalkyl, and heterocyclic groups are the same as those described above. Alkoxy groups may be those having 1 to 20 carbon atoms, preferably those having 1 to 6 carbon atoms. Examples of alkoxy groups include methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, cyclohexyloxy, tetrahydrofuranyloxy, tetrahydropyranyloxy, methoxypropyloxy, ethoxyethyloxy, methoxymethyloxy, and ethoxymethyloxy. Additionally, the alkoxy group may be optionally substituted. 
     Aryloxy—as used herein, is represented by —O-aryl or —O-heteroaryl. Examples and preferred examples of aryl and heteroaryl are the same as those described above. Aryloxy groups may be those having 6 to 30 carbon atoms, preferably those having 6 to 20 carbon atoms. Examples of aryloxy groups include phenoxy and biphenyloxy. Additionally, the aryloxy group may be optionally substituted. 
     Arylalkyl—as used herein, contemplates alkyl substituted with an aryl group. Arylalkyl may be those having 7 to 30 carbon atoms, preferably those having 7 to 20 carbon atoms, and more preferably those having 7 to 13 carbon atoms. Examples of arylalkyl groups include benzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylisopropyl, 2-phenylisopropyl, phenyl-t-butyl, alpha-naphthylmethyl, 1-alpha-naphthylethyl, 2-alpha-naphthylethyl, 1-alpha-naphthylisopropyl, 2-alpha-naphthylisopropyl, beta-naphthylmethyl, 1-beta-naphthylethyl, 2-beta-naphthylethyl, 1-beta-naphthylisopropyl, 2-beta-naphthylisopropyl, p-methylbenzyl, m-methylbenzyl, o-methylbenzyl, p-chlorobenzyl, m-chlorobenzyl, o-chlorobenzyl, p-bromobenzyl, m-bromobenzyl, o-bromobenzyl, p-iodobenzyl, m-iodobenzyl, o-iodobenzyl, p-hydroxybenzyl, m-hydroxybenzyl, o-hydroxybenzyl, p-aminobenzyl, m-aminobenzyl, o-aminobenzyl, p-nitrobenzyl, m-nitrobenzyl, o-nitrobenzyl, p-cyanobenzyl, m-cyanobenzyl, o-cyanobenzyl, 1-hydroxy-2-phenylisopropyl, and 1-chloro-2-phenylisopropyl. Of the above, preferred are benzyl, p-cyanobenzyl, m-cyanobenzyl, o-cyanobenzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylisopropyl, and 2-phenylisopropyl. Additionally, the arylalkyl group may be optionally substituted. 
     Alkylsilyl—as used herein, contemplates a silyl group substituted with an alkyl group. Alkylsilyl groups may be those having 3 to 20 carbon atoms, preferably those having 3 to 10 carbon atoms. Examples of alkylsilyl groups include trimethylsilyl, triethylsilyl, methyldiethylsilyl, ethyldimethylsilyl, tripropylsilyl, tributylsilyl, triisopropylsilyl, methyldiisopropylsilyl, dimethylisopropylsilyl, tri-t-butylsilyl, triisobutylsilyl, dimethyl t-butylsilyl, and methyldi-t-butylsilyl. Additionally, the alkylsilyl group may be optionally substituted. 
     Arylsilyl—as used herein, contemplates a silyl group substituted with at least one aryl group. Arylsilyl groups may be those having 6 to 30 carbon atoms, preferably those having 8 to 20 carbon atoms. Examples of arylsilyl groups include triphenylsilyl, phenyldibiphenylylsilyl, diphenylbiphenylsilyl, phenyldiethylsilyl, diphenylethylsilyl, phenyldimethylsilyl, diphenylmethylsilyl, phenyldiisopropylsilyl, diphenylisopropylsilyl, diphenylbutylsilyl, diphenylisobutylsilyl, diphenyl t-butylsilyl. Additionally, the arylsilyl group may be optionally substituted. 
     The term “aza” in azadibenzofuran, azadibenzothiophene, etc. means that one or more of C—H groups in the respective aromatic fragment are replaced by a nitrogen atom. For example, azatriphenylene encompasses dibenzo[f,h]quinoxaline, dibenzo[f,h]quinoline and other analogs with two or more nitrogens in the ring system. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein. 
     In the present disclosure, unless otherwise defined, when any term of the group consisting of substituted alkyl, substituted cycloalkyl, substituted heteroalkyl, substituted heterocyclic group, substituted arylalkyl, substituted alkoxy, substituted aryloxy, substituted alkenyl, substituted alkynyl, substituted aryl, substituted heteroaryl, substituted alkylsilyl, substituted arylsilyl, substituted amino, substituted acyl, substituted carbonyl, a substituted carboxylic acid group, a substituted ester group, substituted sulfinyl, substituted sulfonyl, and substituted phosphino is used, it means that any group of alkyl, cycloalkyl, heteroalkyl, heterocyclic group, arylalkyl, alkoxy, aryloxy, alkenyl, alkynyl, aryl, heteroaryl, alkylsilyl, arylsilyl, amino, acyl, carbonyl, a carboxylic acid group, an ester group, sulfinyl, sulfonyl, and phosphino may be substituted with one or more moieties selected from the group consisting of deuterium, halogen, unsubstituted alkyl having 1 to 20 carbon atoms, unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, unsubstituted heteroalkyl having 1 to 20 carbon atoms, an unsubstituted heterocyclic group having 3 to 20 ring atoms, unsubstituted arylalkyl having 7 to 30 carbon atoms, unsubstituted alkoxy having 1 to 20 carbon atoms, unsubstituted aryloxy having 6 to 30 carbon atoms, unsubstituted alkenyl having 2 to 20 carbon atoms, unsubstituted alkynyl having 2 to 20 carbon atoms, unsubstituted aryl having 6 to 30 carbon atoms, unsubstituted heteroaryl having 3 to 30 carbon atoms, unsubstituted alkylsilyl having 3 to 20 carbon atoms, unsubstituted arylsilyl group having 6 to 20 carbon atoms, unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof. 
     It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuranyl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or an attached fragment are considered to be equivalent. 
     In the compounds mentioned in the present disclosure, hydrogen atoms may be partially or fully replaced by deuterium. Other atoms such as carbon and nitrogen may also be replaced by their other stable isotopes. The replacement by other stable isotopes in the compounds may be preferred due to its enhancements of device efficiency and stability. 
     In the compounds mentioned in the present disclosure, multiple substitution refers to a range that includes a di-substitution, up to the maximum available substitution. When substitution in the compounds mentioned in the present disclosure represents multiple substitution (including di-, tri-, and tetra-substitutions etc.), that means the substituent may exist at a plurality of available substitution positions on its linking structure, the substituents present at a plurality of available substitution positions may have the same structure or different structures. 
     In the compounds mentioned in the present disclosure, adjacent substituents in the compounds cannot be joined to form a ring unless otherwise explicitly defined, for example, adjacent substituents can be optionally joined to form a ring. In the compounds mentioned in the present disclosure, the expression that adjacent substituents can be optionally joined to form a ring includes a case where adjacent substituents may be joined to form a ring and a case where adjacent substituents are not joined to form a ring. When adjacent substituents can be optionally joined to form a ring, the ring formed may be monocyclic or polycyclic, as well as alicyclic, heteroalicyclic, aromatic, or heteroaromatic. In such expression, adjacent substituents may refer to substituents bonded to the same atom, substituents bonded to carbon atoms which are directly bonded to each other, or substituents bonded to carbon atoms which are more distant from each other. Preferably, adjacent substituents refer to substituents bonded to the same carbon atom and substituents bonded to carbon atoms which are directly bonded to each other. 
     The expression that adjacent substituents can be optionally joined to form a ring is also intended to mean that two substituents bonded to the same carbon atom are joined to each other via a chemical bond to form a ring, which can be exemplified by the following formula: 
     
       
         
         
             
             
         
       
     
     The expression that adjacent substituents can be optionally joined to form a ring is also intended to mean that two substituents bonded to carbon atoms which are directly bonded to each other are joined to each other via a chemical bond to form a ring, which can be exemplified by the following formula: 
     
       
         
         
             
             
         
       
     
     Furthermore, the expression that adjacent substituents can be optionally joined to form a ring is also intended to mean that, in the case where one of the two substituents bonded to carbon atoms which are directly bonded to each other represents hydrogen, the second substituent is bonded at a position at which the hydrogen atom is bonded, thereby forming a ring. This is exemplified by the following formula: 
     
       
         
         
             
             
         
       
     
     According to an embodiment of the present disclosure, disclosed is an electroluminescent device comprising: 
     an anode, 
     a cathode, and 
     an organic layer disposed between the anode and the cathode, wherein the organic layer comprises at least a first compound and a second compound; 
     wherein the first compound has a structure of H-L-Ar, wherein H has a structure represented by Formula 1: 
     
       
         
         
             
             
         
       
     
     wherein in Formula 1, 
     A 1 , A 2  and A 3  are, at each occurrence identically or differently, selected from N or CR, and the ring A, the ring B and the ring C are, at each occurrence identically or differently, selected from a carbocyclic ring having 5 to 18 carbon atoms or a heterocyclic ring having 3 to 18 carbon atoms; 
     R x  represents, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
     Ar is selected from substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted arylamino having 3 to 30 carbon atoms or a combination thereof; 
     L is selected from a single bond, substituted or unsubstituted arylene having 6 to 30 carbon atoms, substituted or unsubstituted heteroarylene having 3 to 30 carbon atoms or a combination thereof; 
     R and R x  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
     adjacent substituents R, R x  can be optionally joined to form a ring; and 
     “*” represents a position where H is joined to L; 
     wherein the second compound has a structure represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     wherein in Formula 2, 
     Z is selected from O or S; 
     Z 1  to Z 8  are selected from C, N or CR z , and one of Z 1  to Z 4  is C and joined to L 3 ; 
     Ar 1  and Ar 2  are, at each occurrence identically or differently, selected from substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms or a combination thereof; 
     L 1  and L 2  are, at each occurrence identically or differently, selected from a single bond, substituted or unsubstituted arylene having 6 to 30 carbon atoms, substituted or unsubstituted heteroarylene having 3 to 30 carbon atoms or a combination thereof; 
     L 3  is selected from a single bond or substituted or unsubstituted arylene having 6 to 30 carbon atoms; 
     R z  is, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
     adjacent substituents R z  can be optionally joined to form a ring. 
     In the present disclosure, the expression that “adjacent substituents R, R x  can be optionally joined to form a ring” is intended to mean that any one or more of groups of adjacent substituents, such as two adjacent substituents R, two adjacent substituents R x , and adjacent substituents R and R x , can be joined to form a ring. Obviously, for those skilled in the art, it is possible that none of these groups of adjacent substituents are joined to form a ring. 
     In the present disclosure, the expression that “adjacent substituents R z  can be optionally joined to form a ring” is intended to mean that any one or more of groups of adjacent substituents, such as two adjacent substituents R z , can be joined to form a ring. Obviously, for those skilled in the art, it is possible that none of these groups of adjacent substituents are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, in the first compound, the ring A, the ring B and the ring C are, at each occurrence identically or differently, selected from a five-membered carbocyclic ring, an aromatic ring having 6 to 18 carbon atoms or a heteroaromatic ring having 3 to 18 carbon atoms. 
     According to an embodiment of the present disclosure, wherein, in the first compound, the ring A, the ring B and the ring C are, at each occurrence identically or differently, selected from a five-membered carbocyclic ring, a benzene ring, a five-membered heteroaromatic ring or a six-membered heteroaromatic ring. 
     According to an embodiment of the present disclosure, wherein, in the first compound, H has a structure represented by Formula 1A: 
     
       
         
         
             
             
         
       
     
     wherein A 1  to A 3  are, at each occurrence identically or differently, selected from N or CR, and X 1  to X 10  are, at each occurrence identically or differently, selected from N or CR x ; 
     R and R x  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
     adjacent substituents R, R x  can be optionally joined to form a ring; 
     preferably, R and R x  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, at least one of R and R x  is selected from deuterium, halogen, a cyano group, a hydroxyl group, a sulfanyl group, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms or a combination thereof; and 
     adjacent substituents R, R x  can be optionally joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, at least one of R and R x  is selected from deuterium, fluorine, cyano, hydroxyl, sulfanyl, methyl, trideuteromethyl, vinyl, phenyl, biphenyl, naphthyl, 4-cyanophenyl, dibenzofuranyl, dibenzothienyl, triphenylenyl, carbazolyl, 9-phenylcarbazolyl, 9,9-dimethylfluorenyl, pyridyl, phenylpyridyl or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, at least one of R and R x  is selected from deuterium, phenyl, biphenyl or naphthyl. 
     According to an embodiment of the present disclosure, wherein, H is selected from any one of the group consisting of H-1 to H-139, wherein for the specific structures of H-1 to H-139, reference is made to claim  5 . 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures H-1 to H-139 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, Ar is selected from a structure represented by any one of the group consisting of Formula 1-a to Formula 1-d: 
     
       
         
         
             
             
         
       
     
     wherein E is, at each occurrence identically or differently, selected from N or CR e ; 
     Q is selected from NR q , O, S, SiR q R q , CR q R q , BR q  or PR q ; preferably, Q is selected from NR q , O, S or CR q R q ; 
     R e  and R q  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
     adjacent substituents R q , R e  can be optionally joined to form a ring; and 
     
       
         
         
             
             
         
       
     
     represents a position where Ar is joined to L. 
     In this embodiment, the expression that “adjacent substituents R q , R e  can be optionally joined to form a ring” is intended to mean that any one or more of groups of adjacent substituents, such as two adjacent substituents R q , two adjacent substituents R e , and adjacent substituents R q  and R e , can be joined to form a ring. Obviously, for those skilled in the art, it is possible that none of these groups of adjacent substituents are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, R q  and R e  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, a cyano group and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, R q  and R e  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, fluorine, cyano, methyl, ethyl, propyl, isopropyl, phenyl, biphenyl, naphthyl, 9-phenylcarbazolyl, naphthylphenyl, phenylpyridyl, dibenzofuranyl, dibenzothienyl, 9,9-dimethylfluorenyl, carbazolyl, pyridyl, pyrimidyl, 4-cyanophenyl, triphenylenyl, terphenyl and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, in Formula 1-c, Q is selected from NR q , O, S or CR q R q . 
     According to an embodiment of the present disclosure, wherein, Ar is, at each occurrence identically or differently, selected from substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted triazinyl, substituted or unsubstituted quinazolinyl, substituted or unsubstituted quinoxalinyl, substituted or unsubstituted dibenzofuranyl, substituted or unsubstituted dibenzothienyl, substituted or unsubstituted azadibenzofuranyl, substituted or unsubstituted azadibenzothienyl, substituted or unsubstituted carbazolyl, substituted or unsubstituted fluorenyl, substituted or unsubstituted spirodifluorenyl, substituted or unsubstituted diphenylamino or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, Ar is, at each occurrence identically or differently, selected from substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted dibenzofuranyl, substituted or unsubstituted dibenzothienyl, substituted or unsubstituted carbazolyl, substituted or unsubstituted fluorenyl, substituted or unsubstituted spirodifluorenyl or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, Ar is selected from any one of the group consisting of Ar-1 to Ar-130, wherein for the specific structures of Ar-1 to Ar-130, reference is made to claim  9 . 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures Ar-1 to Ar-130 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, L is selected from any one of the group consisting of L-0 to L-29, wherein for the specific structures of L-0 to L-29, reference is made to claim  10 . 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures L-0 to L-29 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, the first compound has the structure of H-L-Ar; wherein H is selected from any one of the group consisting of H-1 to H-139, wherein for the specific structures of H-1 to H-139, reference is made to claim  5 ; Ar is selected from any one of the group consisting of Ar-1 to Ar-130, wherein for the specific structures of Ar-1 to Ar-130, reference is made to claim  9 ; L is selected from any one of the group consisting of L-0 to L-29, wherein for the specific structures of L-0 to L-29, reference is made to claim  10 ; and optionally, hydrogen in the compound can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, the first compound is selected from the group consisting of Compound 1 to Compound 772. For the specific structures of Compound 1 to Compound 772, reference is made to claim  11 . 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures of Compound 1 to Compound 772 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, the second compound has a maximum phosphorescence emission wavelength of less than or equal to 580 nm at 77 K. 
     According to an embodiment of the present disclosure, wherein, the second compound has a maximum phosphorescence emission wavelength of less than or equal to 560 nm at 77 K. 
     According to an embodiment of the present disclosure, wherein, the second compound has a maximum phosphorescence emission wavelength of greater than or equal to 460 nm and less than or equal to 580 nm at 77 K. 
     According to an embodiment of the present disclosure, wherein, the second compound has a maximum phosphorescence emission wavelength of greater than or equal to 460 nm and less than or equal to 560 nm at 77 K. 
     According to an embodiment of the present disclosure, wherein, the second compound has a structure represented by Formula 2-1, Formula 2-2 or Formula 2-3: 
     
       
         
         
             
             
         
       
     
     wherein 
     Z is selected from O or S; 
     Z 1  to Z 8  are selected from C, N or CR z , and one of Z 1  to Z 4  is C and joined to L 3 ; in Formula 2-3, at least another one of Z 1  to Z 8  is C and joined to Ar 3 ; 
     W 1  to W 8  are, at each occurrence identically or differently, selected from N, C or CR w ; in Formula 2-2, at least one of W 1  to W 4  is C and joined to L 1 ; 
     L 1  and L 2  are, at each occurrence identically or differently, selected from a single bond, substituted or unsubstituted arylene having 6 to 30 carbon atoms, substituted or unsubstituted heteroarylene having 3 to 30 carbon atoms or a combination thereof; 
     L 3  is selected from a single bond, substituted or unsubstituted arylene having 6 to 30 carbon atoms or a combination thereof; 
     R n , R z  and R w  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
     Ar 1 , Ar 2  and Ar 3  are selected from substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms or a combination thereof; and 
     adjacent substituents R z , R w  and R n  can be optionally joined to form a ring. 
     In this embodiment, the expression that “adjacent substituents R z , R w , R n  can be optionally joined to form a ring” is intended to mean that any one or more of groups of adjacent substituents, such as two adjacent substituents R z , two adjacent substituents R w , and adjacent substituents R w  and R n , can be joined to form a ring. Obviously, for those skilled in the art, it is possible that none of these groups of adjacent substituents are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, Ar 1 , Ar 2  and Ar 3  are, at each occurrence identically or differently, selected from substituted or unsubstituted aryl having 6 to 18 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 18 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, Ar 1 , Ar 2  and Ar 3  are, at each occurrence identically or differently, selected from substituted or unsubstituted phenyl, substituted or unsubstituted biphenyl, substituted or unsubstituted terphenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted dibenzofuranyl, substituted or unsubstituted dibenzothienyl, substituted or unsubstituted carbazolyl, substituted or unsubstituted phenanthryl, substituted or unsubstituted triphenylenyl, substituted or unsubstituted fluorenyl or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, Ar 1 , Ar 2  and Ar 3  are, at each occurrence identically or differently, selected from any one of the group consisting of Ar1 to Ar130, wherein for the specific structures of Ar1 to Ar130, reference is made to claim  14 . 
     According to an embodiment of the present disclosure, wherein, Ar 1 , Ar 2  and Ar 3  are, at each occurrence identically or differently, selected from any one of the group consisting of Ar1 to Ar132, wherein for the specific structures of Ar1 to Ar132, reference is made to claim  14 . 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures Ar1 to Ar130 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures Ar1 to Ar132 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, R z , R w  and R n  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, cyano, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms and combinations thereof. 
     According to an embodiment of the present disclosure, wherein, R z , R w  and R n  are, at each occurrence identically or differently, selected from hydrogen, deuterium, halogen, cyano, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, R z , R w  and R n  are, at each occurrence identically or differently, selected from hydrogen, deuterium, cyano, phenyl, biphenyl, naphthyl, dibenzofuranyl, dibenzothienyl, carbazolyl, 9-phenylcarbazolyl, 9,9-dimethylfluorenyl or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, L 1  and L 2  are, at each occurrence identically or differently, selected from a single bond, substituted or unsubstituted arylene having 6 to 18 carbon atoms, substituted or unsubstituted heteroarylene having 3 to 18 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, L 3  is, at each occurrence identically or differently, selected from a single bond, substituted or unsubstituted arylene having 6 to 18 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, L 1 , L 2  and L 3  are, at each occurrence identically or differently, selected from a single bond, substituted or unsubstituted phenylene, substituted or unsubstituted naphthylene, substituted or unsubstituted biphenylene or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, L 1 , L 2  and L 3  are, at each occurrence identically or differently, selected from the group consisting of: a single bond, phenylene, naphthylene and biphenylene; and optionally, hydrogen in the above structures can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, the second compound is selected from any one of the group consisting of G-1 to G-205, wherein for the specific structures of G-1 to G-205, reference is made to claim  17 . 
     According to an embodiment of the present disclosure, wherein, the second compound is selected from any one of the group consisting of G-1 to G-210, wherein for the specific structures of G-1 to G-210, reference is made to claim  17 . 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures G-1 to G-205 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, hydrogen in the structures G-1 to G-210 can be partially or fully substituted with deuterium. 
     According to an embodiment of the present disclosure, wherein, in the electroluminescent device, the organic layer is a light-emitting layer, and the first compound and the second compound are host materials. 
     According to an embodiment of the present disclosure, wherein, in the electroluminescent device, the organic layer further includes at least one phosphorescent material. 
     According to an embodiment of the present disclosure, wherein, the phosphorescent material is a metal complex having a general formula of M(L a ) m (L b ) n (L c ) q ; wherein 
     M is selected from a metal with a relative atomic mass greater than 40; 
     L a , L b  and L c  are a first ligand, a second ligand and a third ligand coordinated to M, respectively; L a , L b  and L c  can be optionally joined to form a multidentate ligand; for example, any two of L a , L b  and L c  may be joined to form a tetradentate ligand; in another example, L a , L b  and L c  may be joined to each other to form a hexadentate ligand; in another example, none of L a , L b  and L c  are joined so that the multidentate ligand is not formed; and 
     L a , L b  and L c  may be identical or different; m is 1, 2 or 3, n is 0, 1 or 2, q is 0 or 1, and m+n+q equals the oxidation state of M; when m is greater than or equal to 2, a plurality of L a  may be identical or different; when n is equal to 2, two L b  may be identical or different; 
     wherein L a  has a structure represented by Formula 3: 
     
       
         
         
             
             
         
       
     
     wherein 
     the ring D is selected from a five-membered heteroaromatic ring or a six-membered heteroaromatic ring; 
     the ring F is selected from a five-membered unsaturated carbocyclic ring, a benzene ring, a five-membered heteroaromatic ring or a six-membered heteroaromatic ring; 
     the ring D and the ring F are fused via U a  and U b ; 
     U a  and U b  are, at each occurrence identically or differently, selected from C or N; 
     R d  and R f  represent, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
     V 1  to V 4  are, at each occurrence identically or differently, selected from CR v  or N; 
     R d , R f  and R v  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
     adjacent substituents R d , R f , R v  can be optionally joined to form a ring; 
     wherein L b  and L c  are, at each occurrence identically or differently, selected from any one of the following structures: 
     
       
         
         
             
             
         
       
     
     wherein 
     R a , R b  and R c  represent, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
     X b  is, at each occurrence identically or differently, selected from the group consisting of: O, S, Se, NR N1  and CR C1 R C2 ; 
     X c  and X d  are, at each occurrence identically or differently, selected from the group consisting of: O, S, Se and NR N2 ; 
     R a , R b , R c , R N1 , R N2 , R C1  and R C2  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
     in the structures of the ligands L b  and L c , adjacent substituents R a , R b , R c , R N1 , R N2 , R C1  and R C2  can be optionally joined to form a ring. 
     In the present disclosure, the expression that “adjacent substituents R d , R f , R v  can be optionally joined to form a ring” is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R d , two substituents R f , two substituents R v , substituents R d  and R f , and substituents R d  and R v , can be joined to form a ring. Obviously, it is possible that none of these substituents are joined to form a ring. 
     In the present disclosure, the expression that “adjacent substituents R a , R b , R c , R N1 , R C1  and R C2  can be optionally joined to form a ring” is intended to mean that any one or more of groups of adjacent substituents, such as two substituents R a , two substituents R b , two substituents R c , substituents R a  and R b , substituents R a  and R c , substituents R b  and R c , substituents R a  and R N1 , substituents R b  and R N1 , substituents R a  and R C1 , substituents R a  and R C2 , substituents R b  and R C1 , substituents R b  and R C2 , and substituents R C1  and R C2 , can be joined to form a ring. Obviously, it is possible that none of these substituents are joined to form a ring. 
     According to an embodiment of the present disclosure, wherein, the phosphorescent material is a metal complex having a general formula of M(L a ) m (L b ) n ; wherein 
     M is selected from a metal with a relative atomic mass greater than 40; 
     L a  and L b  are a first ligand and a second ligand coordinated to M, respectively; L a  and L b  can be optionally joined to form a multidentate ligand; for example, L a  and L b  may be joined to form a tetradentate ligand; in another example, L a  and L b  may be joined to each other to form a hexadentate ligand; in another example, none of L a  and L b  are joined so that the multidentate ligand is not formed; and 
     m is 1, 2 or 3, n is 0, 1 or 2, and m+n equals the oxidation state of M; wherein when m is greater than or equal to 2, a plurality of L a  may be identical or different; when n is equal to 2, two L b  may be identical or different; 
     wherein L a  has a structure represented by Formula 3: 
     
       
         
         
             
             
         
       
     
     wherein 
     the ring D is selected from a five-membered heteroaromatic ring or a six-membered heteroaromatic ring; 
     the ring F is selected from a five-membered unsaturated carbocyclic ring, a benzene ring, a five-membered heteroaromatic ring or a six-membered heteroaromatic ring; 
     the ring D and the ring F are fused via U a  and U b ; 
     U a  and U b  are, at each occurrence identically or differently, selected from C or N; 
     R d  and R f  represent, at each occurrence identically or differently, mono-substitution, multiple substitutions or non-substitution; 
     V 1  to V 4  are, at each occurrence identically or differently, selected from CR v  or N; 
     R d , R f  and R v  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; and 
     adjacent substituents R d , R f , R v  can be optionally joined to form a ring; 
     wherein the ligand L b  has the following structure: 
     
       
         
         
             
             
         
       
     
     wherein R 1  to R 7  are, at each occurrence identically or differently, selected from the group consisting of: hydrogen, deuterium, halogen, substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms, a substituted or unsubstituted heterocyclic group having 3 to 20 ring atoms, substituted or unsubstituted arylalkyl having 7 to 30 carbon atoms, substituted or unsubstituted alkoxy having 1 to 20 carbon atoms, substituted or unsubstituted aryloxy having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl having 2 to 20 carbon atoms, substituted or unsubstituted aryl having 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl having 3 to 30 carbon atoms, substituted or unsubstituted alkylsilyl having 3 to 20 carbon atoms, substituted or unsubstituted arylsilyl having 6 to 20 carbon atoms, substituted or unsubstituted amino having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a cyano group, an isocyano group, a hydroxyl group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
     preferably, at least one or two of R 1  to R 3  is(are) selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof; and/or at least one or two of R 4  to R 6  is(are) selected from substituted or unsubstituted alkyl having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 1 to 20 carbon atoms or a combination thereof; 
     more preferably, at least two of R 1  to R 3  are, at each occurrence identically or differently, selected from substituted or unsubstituted alkyl having 2 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 2 to 20 carbon atoms or a combination thereof; and/or at least two of R 4  to R 6  are, at each occurrence identically or differently, selected from substituted or unsubstituted alkyl having 2 to 20 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 20 ring carbon atoms, substituted or unsubstituted heteroalkyl having 2 to 20 carbon atoms or a combination thereof. 
     According to an embodiment of the present disclosure, wherein, the metal M is selected from Ir, Pt or Os. 
     According to an embodiment of the present disclosure, wherein, the phosphorescent material is a complex of Ir, which has a structure represented by any one of Ir(L a )(L b )(L c ), Ir(L a ) 2 (L b ), Ir(L a )(L b ) 2 , Ir(L a ) 2 (L c ) or Ir(L a )(L c ) 2 . 
     According to an embodiment of the present disclosure, wherein, the phosphorescent material is a metal complex, and the metal complex is a complex of Ir, which has a structure represented by any one of Ir(L a )(L b )(L c ), Ir(L a ) 2 (L b ), Ir(L a )(L b ) 2 , Ir(L a ) 2 (L c ) or Ir(L a )(L c ) 2 ; wherein 
     L a  has a structure represented by Formula 3 and contains at least one structural unit selected from the group consisting of an aromatic ring formed by fusing a six-membered ring to a six-membered ring, a heteroaromatic ring formed by fusing a six-membered ring to a six-membered ring and a heteroaromatic ring formed by fusing a six-membered ring to a five-membered ring; 
     preferably, L a  has a structure represented by Formula 3 and contains at least one structural unit selected from the group consisting of naphthalene, phenanthrene, quinoline, isoquinoline and azaphenanthrene; 
     more preferably, L a  is, at each occurrence, selected from any one of the following structures: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     preferably, L b  is, at each occurrence, selected from any one of the following structures: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     According to an embodiment of the present disclosure, wherein, the phosphorescent material is selected from the group consisting of the following structures: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     According to an embodiment of the present disclosure, further disclosed is a compound composition comprising the first compound and the second compound in the preceding embodiment. 
     According to an embodiment of the present disclosure, further disclosed is a display assembly comprising the electroluminescent device in the preceding embodiment. 
     Combination with Other Materials 
     The materials described in the present disclosure for a particular layer in an organic light emitting device can be used in combination with various other materials present in the device. The combinations of these materials are described in more detail in U.S. Pat. App. No. 20160359122 at paragraphs 0132-0161, which is incorporated by reference herein in its entirety. 
     The materials described or referred to the disclosure are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination. 
     The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a variety of other materials present in the device. For example, dopants disclosed herein may be used in combination with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The combination of these materials is described in detail in paragraphs 0080-0101 of U.S. Pat. App. No. 20150349273, which is incorporated by reference herein in its entirety. The materials described or referred to the disclosure are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination. 
     Methods for preparing a first compound and a second compound selected herein are not limited in the present disclosure. Those skilled in the art can prepare the first compound and the second compound by conventional synthesis methods or can refer to the preparation methods in Patent Application Nos. US2018337340A1, US2016141508A1, US2014312338A1, US2015171340A1 and other patent applications. The preparation methods are not repeated herein. The method for preparing an electroluminescent device is not limited. The preparation method in the following example is merely an example and not to be construed as a limitation. Those skilled in the art can make reasonable improvements on the preparation method in the following example based on the related art. Exemplarily, the proportions of various materials in a light-emitting layer are not particularly limited. Those skilled in the art can reasonably select the proportions within a certain range based on the related art. For example, taking the total weight of the materials in the light-emitting layer as reference, a host material may account for 80% to 99%, and a light-emitting material may account for 1% to 20%; alternatively, the host material may account for 90% to 98%, and the light-emitting material may account for 2% to 10%. Further, the host material may be two materials, where a ratio of the two host materials may be 99:1 to 1:99; alternatively, the ratio may be 80:20 to 20:80; alternatively, the ratio may be 60:40 to 40:60. Characteristics of light-emitting devices prepared in examples are tested using conventional equipment in the art by a method well-known to those skilled in the art. In device examples, the characteristics of the devices are also tested using conventional equipment in the art (including, but not limited to, an evaporator produced by ANGSTROM ENGINEERING, an optical testing system produced by SUZHOU FATAR, a life testing system produced by SUZHOU FATAR, and an ellipsometer produced by BEIJING ELLITOP, etc.) by methods well-known to those skilled in the art. As the persons skilled in the art are aware of the above-mentioned equipment use, test methods and other related contents, the inherent data of the sample can be obtained with certainty and without influence, so the above related contents are not further described in this disclosure. 
     Device Example 
     Device Example 1 
     First, a glass substrate having an Indium Tin Oxide (ITO) anode with a thickness of 120 nm was cleaned and then treated with oxygen plasma and UV ozone. After the treatment, the substrate was dried in a nitrogen-filled glovebox to remove moisture and then mounted on a substrate holder and placed in a vacuum chamber. Organic layers specified below were sequentially deposited through vacuum thermal evaporation on the ITO anode at a rate of 0.01 to 5 Å/s and at a vacuum degree of about 10 −8  torr. Compound HI was used as a hole injection layer (HIL) with a thickness of 100 Å. Compound HT was used as a hole transporting layer (HTL) with a thickness of 400 Å. Compound EB was used as an electron blocking layer (EBL) with a thickness of 50 Å. Then, Compound 117 as a first host, Compound G-64 as a second host and a phosphorescent compound RD were co-deposited as an emissive layer (EML) with a thickness of 400 Å. Compound HB was used as a hole blocking layer (HBL) with a thickness of 50 Å. On the HBL, Compound ET and 8-hydroxyquinolinolato-lithium (Liq) were co-deposited as an electron transporting layer (ETL) with a thickness of 350 Å. Finally, 8-hydroxyquinolinolato-lithium (Liq) was deposited as an electron injection layer (EIL) with a thickness of 10 Å, and A1 was deposited as a cathode with a thickness of 1200 Å. The device was transferred back to the glovebox and encapsulated with a glass lid to complete the device. 
     Device Example 2 
     The implementation mode in Device Example 2 was the same as that in Device Example 1, except that in the EML, Compound 117 was replaced with Compound 84 as the first host. 
     Device Example 3 
     The implementation mode in Device Example 3 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-88 as the second host. 
     Device Example 4 
     The implementation mode in Device Example 4 was the same as that in Device Example 2, except that in the EML, Compound G-64 was replaced with Compound G-96 as the second host. 
     Device Example 5 
     The implementation mode in Device Example 5 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-107 as the second host. 
     Device Example 6 
     The implementation mode in Device Example 6 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-122 as the second host. 
     Device Example 7 
     The implementation mode in Device Example 7 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-134 as the second host. 
     Device Example 8 
     The implementation mode in Device Example 8 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-135 as the second host. 
     Device Example 9 
     The implementation mode in Device Example 9 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-207 as the second host. 
     Device Example 10 
     The implementation mode in Device Example 10 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-208 as the second host. 
     Device Example 11 
     The implementation mode in Device Example 11 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-209 as the second host. 
     Device Example 12 
     The implementation mode in Device Example 12 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound G-210 as the second host. 
     Device Comparative Example 1 
     The implementation mode in Device Comparative Example 1 was the same as that in Device Example 1, except that in the EML, Compound 117 and Compound G-64 were replaced with Compound 117 as a host and Compound 117 and Compound RD were co-deposited as the EML (at a weight ratio of 98:2). 
     Device Comparative Example 2 
     The implementation mode in Device Comparative Example 2 was the same as that in Device Example 1, except that in the EML, Compound 117 and Compound G-64 were replaced with Compound G-64 as a host and Compound G-64 and Compound RD were co-deposited as the EML (at a weight ratio of 98:2). 
     Device Comparative Example 3 
     The implementation mode in Device Comparative Example 3 was the same as that in Device Example 1, except that in the EML, Compound 117 and Compound G-64 were replaced with Compound G-88 as a host and Compound G-88 and Compound RD were co-deposited as the EML (at a weight ratio of 98:2). 
     Device Comparative Example 4 
     The implementation mode in Device Comparative Example 4 was the same as that in Device Example 1, except that in the EML, Compound 117 and Compound G-64 were replaced with Compound G-96 as a host and Compound G-96 and Compound RD were co-deposited as the EML (at a weight ratio of 98:2). 
     Device Comparative Example 5 
     The implementation mode in Device Comparative Example 5 was the same as that in Device Example 1, except that in the EML, Compound G-64 was replaced with Compound HB as the second host. 
     Detailed structures and thicknesses of layers of the devices are shown in Table 1. A layer using more than one material is obtained by doping different compounds at their weight ratio as recorded. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Device structures in device examples and device comparative examples  
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Device ID 
                 HIL 
                 HTL 
                 EBL 
                 EML 
                 HBL 
                 ETL 
               
               
                   
               
               
                 Example 1 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-64:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 2 
                 Compound 
                 Compound 
                 Compound 
                 Compound 84:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-64:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 3 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-88:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 4 
                 Compound 
                 Compound 
                 Compound 
                 Compound 84:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-96:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 5 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-107:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 6 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-122:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 7 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-134:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 8 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-135:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 9 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-207:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 10 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-208:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 11 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-209:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Example 12 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                   
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 G-210:Compound RD 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (68:30:2) (400 Å) 
                   
                 (350 Å) 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                 Example 1 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 RD (98:2) (400 Å) 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                   
                   
                 (350 Å) 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound G-64:Compound 
                 Compound 
                 Compound 
               
               
                 Example 2 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 RD (98:2) (400 Å) 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                   
                   
                 (350 Å) 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound G-88:Compound 
                 Compound 
                 Compound 
               
               
                 Example 3 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 RD (98:2) (400 Å) 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                   
                   
                 (350 Å) 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound G-96:Compound 
                 Compound 
                 Compound 
               
               
                 Example 4 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 RD (98:2) (400 Å) 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                   
                   
                 (350 Å) 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 Compound 
                 Compound 117:Compound 
                 Compound 
                 Compound 
               
               
                 Example 5 
                 HI (100 Å) 
                 HT (400 Å) 
                 EB (50 Å) 
                 HB:Compound RD (68:30:2) 
                 HB (50 Å) 
                 ET:Liq (40:60) 
               
               
                   
                   
                   
                   
                 (400 Å) 
                   
                 (350 Å) 
               
               
                   
               
            
           
         
       
     
     The structures of the materials used in the devices are shown as follows: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The voltage (V), current efficiency (CE) and external quantum efficiency (EQE) of the device were measured at 15 mA/cm 2 . The lifetime (LT97) of the device was measured at a constant current of 80 mA/cm 2 , where the lifetime (LT97) refers to the time for the device to decay to 97% of its initial brightness. The data was recorded and shown in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Device data in examples and comparative examples 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 At 15 mA/cm 2   
                 At 80 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Voltage 
                 CE 
                 EQE 
                 mA/cm 2   
               
               
                 Device ID 
                 EML 
                 (V) 
                 (cd/A) 
                 (%) 
                 LT97 (h) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1 
                 Compound 117:Compound 
                 4.07 
                 20.5 
                 23.51 
                 148 
               
               
                   
                 G-64:Compound RD (68:30:2) 
                   
                   
                   
                   
               
               
                   
                 (400 Å) 
                   
                   
                   
                   
               
               
                 Example 2 
                 Compound 84:Compound 
                 3.76 
                 18.9 
                 21.68 
                 159 
               
               
                   
                 G-64:Compound RD (68:30:2) 
                   
                   
                   
                   
               
               
                   
                 (400 Å) 
                   
                   
                   
                   
               
               
                 Example 3 
                 Compound 117:Compound 
                 4.29 
                 21.33 
                 24.36 
                 136 
               
               
                   
                 G-88:Compound RD (68:30:2) 
                   
                   
                   
                   
               
               
                   
                 (400 Å) 
                   
                   
                   
                   
               
               
                 Example 4 
                 Compound 84:Compound 
                 3.86 
                 18.9 
                 21.71 
                 145 
               
               
                   
                 G-96:Compound RD (68:30:2) 
                   
                   
                   
                   
               
               
                   
                 (400 Å) 
                   
                   
                   
                   
               
               
                 Example 5 
                 Compound 117:Compound 
                 4.19 
                 21.2 
                 24.03 
                 156 
               
               
                   
                 G-107:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 6 
                 Compound 117:Compound 
                 3.97 
                 22.4 
                 25.34 
                 101 
               
               
                   
                 G-122:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 7 
                 Compound 117:Compound 
                 3.95 
                 21.1 
                 23.57 
                 135 
               
               
                   
                 G-134:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 8 
                 Compound 117:Compound 
                 4.31 
                 19.9 
                 22.12 
                 142 
               
               
                   
                 G-135:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 9 
                 Compound 117:Compound 
                 3.95 
                 21.8 
                 25.09 
                 125.0 
               
               
                   
                 G-207:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 10 
                 Compound 117:Compound 
                 4.08 
                 22.1 
                 25.01 
                 137.5 
               
               
                   
                 G-208:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 11 
                 Compound 117:Compound 
                 4.10 
                 22.0 
                 25.06 
                 104.1 
               
               
                   
                 G-209:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Example 12 
                 Compound 117:Compound 
                 4.07 
                 21.9 
                 25.07 
                 118.5 
               
               
                   
                 G-210:Compound RD 
                   
                   
                   
                   
               
               
                   
                 (68:30:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound 117:Compound 
                 4.97 
                 12.19 
                 12.95 
                 15 
               
               
                 Example 1 
                 RD (98:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound G-64:Compound 
                 4.00 
                 17.06 
                 19.58 
                 4.3 
               
               
                 Example 2 
                 RD (98:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound G-88:Compound 
                 4.81 
                 18.59 
                 20.73 
                 10.5 
               
               
                 Example 3 
                 RD (98:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound G-96:Compound 
                 4.70 
                 17.14 
                 19.69 
                 3.5 
               
               
                 Example 4 
                 RD (98:2) (400 Å) 
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound117:Compound 
                 4.15 
                 19.54 
                 22.53 
                 100 
               
               
                 Example 5 
                 HB:Compound RD (68:30:2) 
                   
                   
                   
                   
               
               
                   
                 (400 Å) 
               
               
                   
               
            
           
         
       
     
     DISCUSSION 
     As shown in Table 2, compared to Comparative Example 1 using only Compound 117, Device Example 1, Device Example 3 and Device Example 5 to Device Example 8 using the first compound (Compound 117) of the present disclosure in combination with the second compounds G-64, G-88, G-107, G-122, G-134 and G-135 of the present disclosure, respectively in the emissive layer have significantly extended device lifetimes which are extended to 9.86 times, 9.06 times, 10.4 times, 6.73 times, 9 times and 9.46 times, respectively, significantly reduced voltages, and significantly improved CE and EQE. This indicates that the device containing a combination of the first compound and the second compound of the present disclosure has better performance than the device using only the first compound in all aspects. 
     Compared to Comparative Example 1 using only Compound 117, Example 9 to Example 12 using the first compound (Compound 117) of the present disclosure in combination with the second compounds G-207, G-208, G-209 and G-210 of the present disclosure, respectively in the emissive layer have significantly extended device lifetimes which are extended to 8.33 times, 9.17 times, 6.94 times and 7.9 times, respectively, significantly reduced voltages, and significantly improved CE and EQE. This indicates that the device containing a combination of the first compound and the second compound of the present disclosure has better performance than the device using only the first compound in all aspects. 
     Compared to Comparative Example 2 using only the second compound G-64, Device Example 1 using the first compound (Compound 117) of the present disclosure in combination with the second compound G-64 of the present disclosure in the emissive layer has significantly improved CE, EQE and device lifetime, especially the device lifetime extended to 34.4 times. Similarly, compared to Comparative Example 2, Comparative Example 3 and Comparative Example 4, respectively, Device Example 2, Device Example 3 and Device Example 4 have device lifetimes extended to 36.9 times, 12.9 times and 41.4 times, significantly reduced voltages and significantly improved CE and EQE. This indicates that the device containing a combination of the first compound and the second compound of the present disclosure has better performance than the device using only the second compound in all aspects. 
     The above results show that the electroluminescent device containing the first compound and the second compound of the present disclosure improves device performance in all aspects through a combination of the two compounds while the device using the first compound or the second compound alone is poor in performance. 
     Comparative Example 5 using the first compound (Compound 117) of the present disclosure in combination with the host material (Compound HB) containing a triazine structure which is commonly used in red light-emitting devices has a device voltage of 4.15 V, a CE of 19.54 cd/A, an EQE of 22.53% and a lifetime of 100 h, the voltage and the lifetime of those device examples all exhibit good in performance. However, compared to comparative Example 5, Device Example 1, Device Example 3 and Device Example 5 to Device Example 8 using Compound 117 in combination with the second compound of the present disclosure have more excellent overall performance, and most of the device examples have significantly longer lifetimes than Comparative Example 5 and all of the device examples have improved CE. Although Example 6 has substantially the same lifetime as Comparative Example 5, Example 6 has a 0.18 V lower voltage, 14.6% higher CE and 12.5% higher EQE. This indicates that a combination of the first compound of the present disclosure and the second compound of the present disclosure having the triazine structure can significantly improve the overall performance of the device. 
     In Example 9 to Example 12, the first compound (Compound 117) of the present disclosure is used in combination with the second compounds G-207, G-208, G-209 and G-210 of the present disclosure, respectively in the emissive layer of the device, while in Comparative Example 5, the first compound (Compound 117) of the present disclosure is used in combination with the second compound HB not provided by the present disclosure in the emissive layer of the device. Compared to Comparative Example 5, Example 9 to Example 12 all have reduced voltages and significantly improved CE, EQE and lifetimes. Although the lifetime of Example 11 is a little longer than that of Comparative Example 5, the CE and the EQE of Example 11 are improved by 12.6% and 11.2%, respectively. This indicates that the combination of the first compound of the present disclosure and the second compound of the present disclosure can significantly improve the overall performance of the device. 
     The maximum phosphorescence emission wavelengths of the second compounds of the present disclosure in the examples and Compound HB in the comparative example at 77 K are tested and recorded in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Maximum phosphorescence emission 
               
               
                 wavelengths of compounds at 77K 
               
            
           
           
               
               
               
            
               
                   
                   
                 Maximum Phosphorescence 
               
               
                   
                 Compound 
                 Emission Wavelength at 77K 
               
               
                   
                   
               
               
                   
                 Compound G-64 
                 472 nm 
               
               
                   
                 Compound G-88 
                 560 nm 
               
               
                   
                 Compound G-96 
                 476 nm 
               
               
                   
                 Compound G-107 
                 484 nm 
               
               
                   
                 Compound G-122 
                 477 nm 
               
               
                   
                 Compound G-135 
                 469 nm 
               
               
                   
                 Compound HB 
                 456 nm 
               
               
                   
                 Compound G-207 
                 511 nm 
               
               
                   
                 Compound G-208 
                 499 nm 
               
               
                   
                 Compound G-209 
                 514 nm 
               
               
                   
                 Compound G-210 
                 492 nm 
               
               
                   
                   
               
            
           
         
       
     
     The maximum phosphorescence emission wavelength of Compound HB at 77 K used in the comparative example is 456 nm, while the wavelengths of the second compounds used in the examples are all greater than 460 nm and less than 580 nm, that is, only when the second compound has a triplet energy level lower than the triplet energy level corresponding to a wavelength of 460 nm, can the combination of the second compound with the first compound achieve better device performance. 
     From the above results, it can be seen that the electroluminescent device disclosed in the present disclosure and containing the first compound and the second compound can significantly improve device efficiency and lifetime, reduce device voltage to some extent, and has a broad commercial development prospect and application value. 
     It should be understood that various embodiments described herein are merely examples and not intended to limit the scope of the present disclosure. Therefore, it is apparent to those skilled in the art that the present disclosure as claimed may include variations from specific embodiments and preferred embodiments described herein. Many of materials and structures described herein may be substituted with other materials and structures without departing from the spirit of the present disclosure. It should be understood that various theories as to why the present disclosure works are not intended to be limitative.