An organic electroluminescent device, a display device

Abstract

The present invention belongs to the field of electroluminescence, and discloses an organic electroluminescent device and a display device. The structure of the boron nitride compound is shown in Formula I: Formula I; It is prepared from specific raw materials through processes such as boronization ring-closing reaction, borylation reaction, and Suzuki coupling reaction. The novel boron nitride compound proposed by the present invention can be applied as a narrow-spectrum light-emitting material in the solution-processed OLED process. The introduction of multiple light-emitting cores and bridging groups is beneficial to realizing the regulation of the emission peak position of the material, enabling the material of the present invention to exhibit green light required for practical applications; Based on the improved film-forming performance of the boron nitride compound, the formed light-emitting layer film has a higher in-plane dipole orientation performance, which is beneficial to improving the device efficiency; At the same time, the light-emitting device based on the boron nitride compound has a significant improvement in color purity and a weak concentration dependence, which can improve the process window.

Description

Technical Field

[0001] The present invention belongs to the field of electroluminescence, and particularly relates to an organic electroluminescent device and a display device. Background Art

[0002] With the further improvement of consumers' requirements for the display quality of display screens, the new generation of ultra-high definition display has become the goal pursued by current display technologies. Organic light-emitting materials with narrow spectral emission characteristics are beneficial to achieving a higher display color gamut and have become a research hotspot in recent years. On the other hand, compared with vacuum evaporation technology, printing display technology has the characteristics of high material utilization rate, unrestricted substrate size, and no need for large-size fine metal mask plates, and has unique advantages in medium and large-size display technologies.

[0003] The emitting layer (EML) is the core part of an OLED device and largely determines the specific display performance of an OLED display screen. The external quantum efficiency (EQE) is a core parameter for judging the performance of an OLED device, which is mainly determined by the internal quantum efficiency (IQE) of the light-emitting material and the light coupling output efficiency (ηout). First, in terms of the internal quantum efficiency, TADF materials with a small singlet-triplet energy level difference can effectively utilize triplet excitons for luminescence and can theoretically achieve 100% exciton utilization rate. Multiple resonance-type thermally activated delayed fluorescence molecules with a boron nitride (BN) skeleton also have a high quantum yield; while in terms of the light coupling output efficiency, it is difficult for the emitting layer thin film in the wet process to have a horizontal dipole orientation, resulting in a low light coupling output efficiency. Multiple resonance-induced thermally activated delayed fluorescence molecules (MR-TADF) with a boron nitride (BN) skeleton are an organic light-emitting material with narrow spectral emission characteristics and high efficiency. In the field of organic electroluminescence, the light-emitting material is a key factor determining the performance of an OLED device. However, at present, the types of boron nitride-based materials suitable for solution processing methods are scarce, and more breakthroughs are urgently needed.

[0004] In summary, developing multiple resonance-type thermally activated delayed fluorescence molecules with a boron nitride (BN) skeleton that have good solution processability and can have a certain horizontal dipole orientation is of great significance for the development of the printed OLED industry. Summary of the Invention

[0005] The object of the present invention is to solve the deficiencies of the prior art. Based on this, in the first aspect of the present invention, an organic electroluminescent device is provided, which includes a light-emitting layer. The light-emitting layer includes a light-emitting guest material and a host material. The light-emitting guest material includes a boron nitride compound, and its structure is shown in Formula I:

[0006] Formula I;

[0007] Wherein, R1 is hydrogen or methyl, and R2 is selected from one of hydrogen, C1-C12 alkyl, C1-C12 alkoxy, C3-C10 cycloalkyl, phenyl, carbazolyl, diphenylamino, diphenylamino substituted by at least one C1-C12 alkyl, and carbazolyl substituted by at least one C1-C12 alkyl.

[0008] Compared with the existing boron nitride-based light-emitting materials, the present invention connects multiple BN light-emitting skeleton core units to a B-bridging group-containing group, making the molecular structure show a special twisted structure, and thus achieving the following effects: First, the molecular structure of the boron nitride compound of the present invention can improve the solubility of the organic material in organic solvents, and thus can be applied to solution processing processes; Second, the BN molecular skeleton has multiple resonance effects, which can endow it with narrow spectral characteristics, thereby improving its display color purity and having a high luminous efficiency at the same time; Third, the twisted molecular structure is conducive to suppressing the stacking of light-emitting molecules, thereby reducing the efficiency roll-off of the device and the spectral red shift and spectral broadening caused by molecular stacking; Fourth, by introducing a core B-containing structure, the overall light-emitting material can have certain charge transfer luminescence characteristics, and the emission peak position of the light-emitting material can be regulated; Fifth, the overall molecular structure of the light-emitting material provided by the present invention is conducive to realizing the improvement of the horizontal dipole of the light-emitting layer.

[0009] In some preferred embodiments, the structure of the above boron nitride compound is one of M1-M12:

[0010] .

[0011] In a more preferred embodiment, the structure of the above boron nitride compound is M9 or M11. Their maximum current efficiencies can reach 73.8 cd / A and 76.3 cd / A respectively, and the current efficiencies at 1000 nit brightness can reach 53.0 cd / A and 55.2 cd / A respectively.

[0012] In addition, the present invention provides a preparation method of the above boron nitride compound, including the following steps:

[0013] React raw material 1 with raw material 2 to obtain intermediate 1, and the reaction formula is as follows:

[0014] ;

[0015] The specific process is as follows: Potassium tert-butoxide (2.2 eq) is dissolved in anhydrous DMF to form mixture a, and the carbazole raw material (i.e., raw material 2, 2.2 eq) is dissolved in anhydrous DMF to form mixture b. Under nitrogen atmosphere, mixture b is slowly dropped into mixture a, and stirred at room temperature for 2 hours to form mixture c. The substituted 1-bromo-2,6-difluorobenzene raw material (i.e., raw material 1, 1.0 eq) is dissolved in anhydrous DMF to form mixture d. Mixture d is dropped into mixture c drop by drop, and then heated at 140 °C for 24 hours to form mixture e. After cooling, mixture e is poured into excessive ice water, the precipitate is collected by filtration, and intermediate 1 is obtained by column chromatography.

[0016] The above intermediate 1 is subjected to a boration ring-closing reaction to generate intermediate 2, and the reaction formula is as follows:

[0017] ;

[0018] The specific process is as follows: The above intermediate 1 (1.0 eq) is dissolved in tert-butylbenzene to form mixture f. The temperature is lowered to 0 °C in an ice-water bath, and under nitrogen protection, tert-butyllithium (2.0 eq) is slowly added to mixture f, and heated at 60 °C for 2 hours to form mixture g. Boron tribromide (2.0 eq) is added to mixture g at -30 °C, and stirred at room temperature for 1 hour to form mixture h. N,N-Diisopropylethylamine (2.0 eq) is added to mixture h at 0 °C, and heated at 130 °C for 6 hours to form mixture g. Methanol is added to mixture g to neutralize the remaining boron tribromide in the mixture, and then mixture g is extracted and separated by column chromatography to obtain intermediate 2.

[0019] The above intermediate 2 is subjected to a boronation reaction to generate intermediate 3, and the reaction formula is as follows:

[0020] ;

[0021] The specific process is as follows: The catalyst [Ir(COD)(OCH 3 )] 2 (0.01 eq), 4,4'-Di-tert-butylbipyridine (dtbpy) (0.02 eq), intermediate 2 (1.0 eq) and bis(pinacolato)diboron (B 2 Pin) (1.0 eq) are added to an ultra-dry tetrahydrofuran solvent. After bubbling with nitrogen for 5 minutes, heated under nitrogen atmosphere with reflux stirring for 24 hours. After cooling to room temperature, it is purified by column chromatography to obtain intermediate 3.

[0022] The above intermediate 3 and raw material 3 are subjected to a Suzuki coupling reaction to generate intermediate 4, and the reaction formula is as follows:

[0023] ;

[0024] The specific process is as follows: Intermediate 3 (1.0 eq), raw material 3 (1.1 eq), tetrabutylammonium bromide and tetrakis(triphenylphosphine)palladium are added to an aqueous potassium carbonate solution and tetrahydrofuran, and heated under reflux in a nitrogen atmosphere for 8 hours. After extraction, column chromatography is used for separation to obtain Intermediate 4.

[0025] React the above Intermediate 4 with raw material 4 to form the above boron-nitrogen compound. The reaction formula is as follows:

[0026] ;

[0027] The specific process is as follows: Dissolve Intermediate 4 (2.2 eq) in diethyl ether or tetrahydrofuran, dropwise add n-butyllithium (2.4 eq) under the condition of -78 °C, warm back to 0 °C and stir for 40 min - 60 min, then dropwise add a toluene solution containing 1.0 eq of 9,10-dibromo-9,10-diboraanthracene under the condition of -78 °C, restore to room temperature and stir for 8 - 12 h. After concentrating the reaction solution, extraction and column chromatography are carried out for separation to obtain the above boron-nitrogen compound.

[0028] Among them, the above raw material 2 is one of RM2-1 to RM2-6, and their structures are respectively shown as follows:

[0029] ;

[0030] The above raw material 3 is RM3-1 or RM3-2, and their structures are respectively shown as follows:

[0031] .

[0032] Among them, the content of the above luminescent dopant material is 0.1 wt% - 20 wt%, and the content of the above host material (which can be mCP, mCPBC, CBP, 2,6DCzPPy or mCPCN, etc.) is 80 wt% - 99.9 wt%. The above organic light-emitting device includes an anode, a cathode, and an organic thin film layer disposed between the above anode and cathode. The above organic thin film layer includes the above light-emitting layer, an optional hole injection layer, an optional hole transport layer, an optional one or more electron transport layers, and an optional electron injection layer.

[0033] More specifically, the above organic light-emitting device sequentially includes: an anode, a hole injection layer, a hole transport layer, the light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode. In some other embodiments, it may also include an optional hole blocking layer, an optional electron blocking layer, and an optional capping layer, etc.

[0034] Among them, the light-emitting layer, hole injection layer, and hole transport layer can be prepared by spin coating or inkjet printing processes, while the electron transport layer, electron injection layer, and cathode can be prepared by vacuum evaporation processes.

[0035] The second aspect of the present invention provides a display device, including the above-mentioned organic electroluminescent device.

[0036] The beneficial effects of the present invention are as follows: The novel boron nitride compound proposed by the present invention can be applied in solution-processed OLED processes as a narrow-spectrum light-emitting material. The introduction of multiple light-emitting cores and bridging groups is beneficial to realizing the regulation of the emission peak position of the material, enabling the material of the present invention to exhibit green light required for practical applications; the film-forming performance based on this boron nitride compound has been improved, and the formed light-emitting layer film has higher in-plane dipole orientation performance, which is beneficial to improving device efficiency; at the same time, the light-emitting device based on this boron nitride compound has a significant improvement in color purity and a weak concentration dependence, which can improve the process window. Description of the Drawings

[0037] Figure 1 Shown is a schematic structural diagram of an organic electroluminescent device. Among them, 1 is an ITO anode, 2 is a hole injection layer, 3 is a hole transport layer, 4 is a light-emitting layer, 5 is a hole blocking layer, 6 is an electron transport layer, 7 is an electron injection layer, and 8 is a metal cathode. Detailed Embodiments

[0038] The following will clearly and completely describe the concept, specific structure, and technical effects generated by the present invention in combination with embodiments and drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0039] The structures of compounds M1-M12 involved in the following content are respectively shown as follows:

[0040]

[0041] 。

[0042] The synthetic routes of the above compounds M1-M12 are shown as follows:

[0043] React raw material 1 and raw material 2 to obtain intermediate 1, and the reaction formula is as follows:

[0044] ;

[0045] Perform a boronization ring-closing reaction on intermediate 1 to generate intermediate 2, and the reaction formula is as follows:

[0046] ;

[0047] The intermediate 2 is subjected to a borylation reaction to generate intermediate 3, and the reaction formula is as follows:

[0048] ;

[0049] The intermediate 3 and raw material 3 are subjected to a Suzuki coupling reaction to generate intermediate 4, and the reaction formula is as follows:

[0050] ;

[0051] The intermediate 4 and raw material 4 are reacted to generate the boron nitride compound, and the reaction formula is as follows:

[0052] .

[0053] Among them, raw material 2 includes RM2-1 to RM2-6, and their structures are respectively shown as follows:

[0054] .

[0055] Raw material 3 includes RM3-1 or RM3-2, and their structures are respectively shown as follows:

[0056] .

[0057] The structures of mCPBC, PEDOT:PSS, mCP, 3NT2T, Liq, CM1, CM2, CM3, and CM4 involved in the following content are shown as follows:

[0058]

[0059]

[0060] .

[0061] In addition, in the following content, the molecular mass spectrometry data (Mass Spectra: MS) of molecules with a relative molecular weight below 1000 were measured by an ITQ1100 ion trap gas chromatography-mass spectrometry instrument of Thermo Fisher Company, and the molecular mass spectrometry data of molecules with a relative molecular weight above 1000 were measured by an Autoflex Speed matrix-assisted laser desorption / ionization time-of-flight mass spectrometry instrument of Bruker Company. The elemental analysis of the final product was performed using a Flash EA1112 instrument of Elemental analysis Company.

[0062] Preparation Example

[0063] A boron nitride compound, the structure of which is shown as compound M9; its preparation method includes the following steps:

[0064] (1) Potassium tert-butoxide (2.46 g, 22 mmol) was added to a 250 mL two-necked flask and dissolved in 50 mL of anhydrous DMF. Then, under a nitrogen atmosphere, starting material 2 (RM2-3, 6.15 g, 22 mmol) dissolved in 100 mL of anhydrous DMF was slowly added thereto, and the mixture was stirred at room temperature for 2 hours. Then, under a nitrogen atmosphere, starting material 1 (1.93 g, 10 mmol) dissolved in 30 mL of anhydrous DMF was added dropwise to the previous mixture, and the mixture was heated at 140 °C for 24 hours. The reaction system was cooled to room temperature, and then the reaction solution was added to 2500 g of excess ice water. The precipitate was collected by filtration, and column chromatography was performed using dichloromethane and petroleum ether as eluents to obtain intermediate 1 (5.34 g) with a yield of 75%.

[0065] (2) Intermediate 1 (7.12 g, 10 mmol) was dissolved in 150 mL of tert-butylbenzene in a 250 mL two-necked flask. The temperature was lowered to 0 °C in an ice-water bath, and a n-hexane solution of tert-butyllithium (15.4 mL, 1.3 mol / L, 20 mmol) was slowly added under nitrogen protection. Then, the temperature was raised to 60 °C and heated for 2 hours. Then, the temperature was lowered to -30 °C, and boron tribromide (1.9 mL, 20 mmol) was added to the reaction solution under a nitrogen atmosphere. After returning to room temperature and stirring for 1 hour, the temperature was lowered to 0 °C. Then, N,N-diisopropylethylamine (2.8 mL, 20 mmol) was added to the reaction solution under a nitrogen atmosphere, and the temperature was raised to 130 °C and heated for 6 hours. Then, 10 mL of methanol was added to the reaction solution to neutralize the remaining boron tribromide in the mixture. After extracting the reaction solution with water and dichloromethane, column chromatography was performed using dichloromethane and petroleum ether as eluents to obtain intermediate 2 (2.63 g) with a yield of 41%.

[0066] (3) The catalyst [Ir(COD)(OCH3)] 2 (33.2 mg, 0.05 mmol), 4,4'-di-tert-butylbipyridine (dtbpy) (26.8 mg, 0.1 mmol), intermediate 2 (3.2 g, 5 mmol) and bis(pinacolato)diboron (B 2 Pin) (1.29 g, 5 mmol) were added to a 250 mL two-necked flask, and then 60 mL of ultra-dry tetrahydrofuran was added thereto. After bubbling with nitrogen for 5 minutes, the mixture was heated under reflux and stirred for 24 hours under a nitrogen atmosphere. After cooling to room temperature, the reaction solution was concentrated under reduced pressure, and column chromatography purification was performed using dichloromethane and petroleum ether to obtain intermediate 3 (3.03 g) with a yield of 79%.

[0067] (4) Add the catalyst tetrakis(triphenylphosphine)palladium (350 mg, 0.3 mmol), tetrabutylammonium bromide (0.1 mg, 0.3 mmol), the above intermediate 3 (7.68 g, 11 mmol), raw material 3 (RM3-2, 3.42 g, mmol), and 50 mL of 1 mol / L aqueous potassium carbonate solution into a 250 mL two-necked flask. Then add 50 mL of ultra-dry tetrahydrofuran to it. Heat under reflux and stir for 8 hours under a nitrogen atmosphere. After cooling to room temperature, extract and concentrate the reaction solution under reduced pressure. Purify it by column chromatography using dichloromethane and petroleum ether to obtain intermediate 4 (5.85 g) with a yield of 71%.

[0068] (5) Under a nitrogen atmosphere, add intermediate 4 (9.05 g, 11 mmol) and 20 mL of dry ether solvent into a 100 mL two-necked flask. Cool down to -78 °C and dropwise add 5.5 mmol of n-butyllithium solution. After the temperature returns to 0 °C, stir for 40 min. Then cool down to -78 °C and dropwise add the toluene solution of raw material 4 (1.67 g, 5 mmol dissolved in 15 mmol of dry toluene solvent). After returning to room temperature, stir and react for 8 h. Then use dichloromethane and aqueous ammonium chloride solution for extraction and separation. After low-pressure rotary concentration of the solvent, separate by column chromatography to obtain 1.03 g of product compound M9 with a yield of 62%.

[0069] According to the above similar preparation method, compounds M1-M8 and compounds M10-M12 are prepared. The elemental analysis (percentage content of C, H, and N in the compound) and mass spectrometry test molecular weight data of the specific raw materials and products used are shown in Table 1.

[0070] Table 1

[0071]

[0072] Test experiments on the properties of boron nitride compounds and light-emitting layer thin films

[0073] (1) Test on the solubility in organic solvents and film-forming property

[0074] Solubility test method: Take 1 mL of solvent, add the corresponding mass x of boron nitride compound to it. After heating at 80 °C for 2 h, observe whether the solution is clear and transparent. If the solution shows a clear and transparent phenomenon, it is considered completely dissolved; otherwise, it is considered not completely dissolved.

[0075] The solubility of compounds M1, M3, M9, M11 and CM1 was compared. The solvents selected were two organic solvents commonly used in solution processing techniques (chlorobenzene and methyl benzoate). These two organic solvents included a low-boiling solvent (boiling point less than 180 °C) and a high-boiling solvent (boiling point greater than or equal to 180 °C), and were somewhat representative. The test results are shown in Table 2.

[0076] Table 2

[0077]

[0078] As can be seen from Table 2, in the present invention, a plurality of BN luminescent skeleton core units are connected together through a central B-containing group to obtain a boron nitride compound with a twisted molecular structure. Compared with the unconnected boron nitride compound (such as CM1), the solubility of the boron nitride compound with a twisted molecular structure of the present invention (such as M1, M3, M9, M11) is significantly improved. The improved solubility is beneficial for the organic material to be applicable to the printing OLED process.

[0079] Film formation uniformity test method: mCPBC was selected as the host material, and a luminescent layer film was prepared by spin coating with a doping concentration of 2 wt%. The RMS value (which can represent its film formation uniformity) was measured using an atomic force microscope. The compounds M1, M3, M9, M11 and CM1 were selected for comparison of film formation uniformity. The results are shown in Table 3.

[0080] Table 3

[0081]

[0082] Through the comparison of the data measured by the atomic force microscope, it can be seen that in the boron nitride compound of the present invention, a plurality of BN luminescent skeleton core units are connected together through a central B-containing group to obtain a boron nitride compound with a twisted molecular structure. Compared with the unconnected boron nitride compound (such as CM1), the film formation uniformity of the boron nitride compound with a twisted molecular structure of the present invention (such as M1, M3, M9, M11) is significantly improved. Uniform film formation is beneficial for improving the efficiency and stability of OLED devices.

[0083] (2) Measurement of the in-plane dipole orientation degree of the luminescent layer film

[0084] mCPBC was selected as the host material, and a luminescent layer film was prepared by spin coating with a doping concentration of 2 wt%. The in-plane dipole orientation degree of the film was measured using an angular-resolved spectroscope. The compounds M1, M3, M9, M11 and CM1, CM2, CM3, CM4 were selected for comparison of the in-plane dipole orientation degree. The results are shown in Table 4.

[0085] Table 4

[0086]

[0087] Through the comparison of the data tested by the horizontal dipole orientation degree, it can be known that the organic light-emitting molecules proposed by the present invention have a better horizontal dipole orientation trend compared with the comparative materials of mononuclear boron-nitrogen compounds (such as CM1), which is beneficial to improving the device efficiency.

[0088] Example 1

[0089] An organic light-emitting device (OLED device) has a structure as Figure 1 shown, successively including: ITO anode 1, hole injection layer 2, hole transport layer 3, light-emitting layer 4, hole blocking layer 5, electron transport layer 6, electron injection layer 7, and metal cathode 8.

[0090] The following is the preparation method of the solution-processed OLED device, including:

[0091] The prefabricated ITO glass is ultrasonically cleaned with cleaning solution, deionized water, and isopropanol for 15 minutes in sequence and then placed in an oven at 70 °C for drying; the dried ITO glass is treated with an ultraviolet ozone cleaning machine for 15 minutes; then 200 μL of Pedot:PSS solution is dropped onto the ITO glass, spin-coated at a speed of 2000 rpm / min for 40 seconds, and then annealed and dried at a temperature of 150 °C for 15 minutes to form a hole injection layer with a thickness of 40 nm; mCPBC is selected as the host material, and the light-emitting materials M1-M12 prepared in the preparation examples are respectively selected as the light-emitting guests, dissolved in chlorobenzene solvent according to a certain mass ratio to form a first mixed solution with a concentration of 12 mg / mL, filtered with a PTFE filter membrane with a pore size of 0.22 μm to form a second mixed solution, 80 μL of the second mixed solution is dropped onto the hole injection layer, spin-coated at a speed of 1800 rpm / min for 30 seconds, and annealed and dried at a temperature of 80 °C for 60 minutes to form a light-emitting layer with a thickness of about 40 nm; the unfinished device is transferred to an evaporation chamber, and in a vacuum atmosphere of 3×10 -5 Pa, an electron transport layer is formed at a rate of 0.05 nm / s with a thickness of 40 nm. Here, the electron transport layer material is 3NT2T; an electron injection layer is formed at a rate of 0.01 nm / s with a thickness of 2 nm. Here, the electron injection layer material is lithium (8-hydroxyquinoline); a cathode layer is formed at a rate of 0.02 nm / s. Here, the cathode layer is made of metal aluminum.

[0092] Finally, organic electroluminescent devices Device1 - Device12 were obtained. Among them, PEDOT:PSS was used as the hole injection layer. In the light-emitting layer, the finally synthesized products M1 - M12 were used as the light-emitting guest materials respectively, mCPBC was used as the host material (the doping concentration of the guest material was 2 wt%), 3NT2T was used as the electron transport material, lithium (8-hydroxyquinoline) was used as the electron injection layer, and Al was used as the metal cathode. Its structure was [ITO / PEDOT:PSS (40 nm) / mCPBC:2.0wt% M1 - M12 (40 nm) / 3NT2T (40 nm) / Liq (2 nm) / Al(100 nm)].

[0093] Example 2

[0094] An organic electroluminescent device (OLED device), which had the same device preparation method as that in Example 1, except that: M9 was selected as the light-emitting guest material and the doping concentrations were changed to 5wt%, 10wt% and 20wt%. Finally, organic electroluminescent devices Device13 - Device15 were obtained.

[0095] Comparative Example 1

[0096] An organic electroluminescent device (OLED device), which had the same device preparation method as that in Example 1, except that: PEDOT:PSS was used as the hole injection layer. In the light-emitting layer, CM1 was used as the light-emitting guest material, mCPBC was used as the host material (the doping concentration was 2 wt%), 3NT2T was used as the electron transport material, lithium (8-hydroxyquinoline) was used as the electron injection layer, and Al was used as the metal cathode. Finally, an organic electroluminescent device Compare 1 was obtained, and its structure was [ITO / PEDOT:PSS (40 nm) / mCPBC:2.0wt% CM1 (40 nm) / 3NT2T (40 nm) / Liq(2 nm) / Al(100 nm)].

[0097] Comparative Example 2

[0098] An organic electroluminescent device (OLED device), which differed from Comparative Example 1 in that: the doping concentrations of the light-emitting guest material CM1 were 5wt%, 10wt% and 20wt% respectively. Finally, organic electroluminescent devices Compare 2 - Compare4 were obtained.

[0099] Comparative Example 3

[0100] An organic electroluminescent device (OLED device), which has the same device preparation method as that of Example 1, except that: PEDOT:PSS is used as the hole injection layer. In the light-emitting layer, CM2 is used as the light-emitting guest material, mCPBC is used as the host material (doping concentration is 2 wt%), 3NT2T is used as the electron transport material, lithium (8-hydroxyquinoline) is used as the electron injection layer, and Al is used as the metal cathode. Finally, an organic electroluminescent device Compare 5 is obtained, and its structure is [ITO / PEDOT:PSS (40 nm) / mCPBC:2.0wt% CM2 (40 nm) / 3NT2T (40 nm) / Liq(2 nm) / Al(100 nm)].

[0101] Comparative Example 4

[0102] An organic electroluminescent device (OLED device), which has the same device preparation method as that of Example 1, except that: PEDOT:PSS is used as the hole injection layer. In the light-emitting layer, CM3 is used as the light-emitting guest material, mCPBC is used as the host material (doping concentration is 2 wt%), 3NT2T is used as the electron transport material, lithium (8-hydroxyquinoline) is used as the electron injection layer, and Al is used as the metal cathode. Finally, an organic electroluminescent device Compare 6 is obtained, and its structure is [ITO / PEDOT:PSS (40 nm) / mCPBC:2.0wt% CM3 (40 nm) / 3NT2T (40 nm) / Liq(2 nm) / Al(100 nm)].

[0103] Comparative Example 5

[0104] An organic electroluminescent device (OLED device), which has the same device preparation method as that of Example 1, except that: PEDOT:PSS is used as the hole injection layer. In the light-emitting layer, CM4 is used as the light-emitting guest material, mCPBC is used as the host material (doping concentration is 2 wt%), 3NT2T is used as the electron transport material, lithium (8-hydroxyquinoline) is used as the electron injection layer, and Al is used as the metal cathode. Finally, an organic electroluminescent device Compare 7 is obtained, and its structure is [ITO / PEDOT:PSS (40 nm) / mCPBC:2.0wt% CM4 (40 nm) / 3NT2T (40 nm) / Liq(2 nm) / Al(100 nm)].

[0105] Performance test of organic electroluminescent device (OLED device)

[0106] The organic electroluminescent devices Device1 - Device15 prepared in Examples 1 - 2 and the organic electroluminescent devices Compare 1 - Compare 5 prepared in Comparative Examples 1 - 3 were tested. The characteristics of the devices such as current, voltage, brightness, and emission spectrum were synchronously tested using a Photo Research PR 655 spectral scanning luminance meter and a Keithley K2400 digital source meter system. The performance test of the devices was carried out at room temperature and ambient atmosphere. The test results are shown in Table 5.

[0107] Table 5

[0108]

[0109] By comparing the device performances of the examples and comparative examples in Table 5, the following conclusions can be drawn: When the boron - nitrogen compound of the present invention is used as the light - emitting guest material of a solution - processed OLED device, the prepared organic electroluminescent device obtains a higher maximum efficiency and maintains a better light color (full - width at half - maximum), and at the same time maintains a higher efficiency at a higher brightness. Meanwhile, it can effectively inhibit the spectral broadening and spectral red - shift caused by the increase in doping concentration, which is beneficial to expanding the process window of the material in device preparation and has stronger applicability. The boron - nitrogen compound of the present invention connects multiple BN light - emitting skeleton core units together through a B - containing bridging group to obtain a boron - nitrogen compound with a twisted molecular structure. Compared with the unconnected boron - nitrogen compound (such as CM1), when the doping concentration of the boron - nitrogen compound with a twisted molecular structure of the present invention increases, the spectral broadening and red - shift of the organic electroluminescent device (such as the comparison between Device9, Device13 - 15 and Compare1 - 5) are inhibited, and the efficiency roll - off is also inhibited.

[0110] By comparing Device 7 - 9 with Compare 5, it can be seen that if the R2 group in the structure of the present invention is adjusted, the light - emitting material of the present invention cannot exhibit green light emission, the device as a whole shows blue - green light emission, and the maximum current efficiency of the device decreases and the spectrum broadens.

[0111] By comparing Device 9 with Compare 6 and Compare 7, it can be seen that due to the change in the core structure, the comparative examples mainly show charge - transfer - state luminescence rather than multi - resonance - form luminescence, the device shows orange - red light, and the full - width at half - maximum broadens.

[0112] In summary, the boron nitride compound of the present invention connects multiple BN luminescent skeleton core units to a B-containing bridging group, achieving improvements in various aspects: the solubility in organic solvents and the film-forming uniformity are improved, the emission peak position is successfully tuned to the green light region while maintaining the narrow spectral emission characteristics, the obtained luminescent layer film has a tendency of horizontal dipole orientation, the prepared organic electroluminescent device has higher efficiency and improved efficiency roll-off, and when the doping concentration is increased, the red shift and broadening of the electroluminescent spectrum are suppressed.

[0113] As described above, only the preferred embodiments of the present invention are given. The present invention is not limited to the above-mentioned embodiments. As long as the same means are used to achieve the technical effects of the present invention, they should fall within the protection scope of the present invention. Within the protection scope of the present invention, various modifications and changes can be made to its technical solutions and / or implementation manners.

Claims

1. An organic electroluminescent device, characterized in that: The invention comprises a light-emitting layer, wherein the light-emitting layer comprises a light-emitting guest material and a host material, wherein the light-emitting guest material comprises a boron nitrogen compound, and the structure of the boron nitrogen compound is one of M1-M12: 。 2. The organic electroluminescent device according to claim 1, characterized in that: The structure of the boron nitrogen compound is M9 or M11.

3. The organic electroluminescent device according to claim 1, characterized in that: The content of the luminescent guest material is 0.1 wt%-20 wt%, and the content of the host material is 80 wt%-99.9 wt%.

4. The organic electroluminescent device according to claim 1, characterized in that: Including in order: Anode, hole transport layer, the light emitting layer, electron transport layer, cathode.

5. The organic electroluminescent device according to claim 4, characterized in that: Including in order: Anode, hole injection layer, hole transport layer, the light emitting layer, hole blocking layer, electron transport layer, electron injection layer, cathode.

6. A display device, characterized in that: An organic electroluminescent device comprising any one of claims 1 to 5.

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