Preparation and application of a class of indoloindoloquinoxaline phenoxazine mr-tadf blue light materials

Abstract

The application belongs to the technical field of organic photoelectric materials, and particularly relates to preparation and application of a kind of indole indole quinoxaline phenoxazine MR-TADF blue light material. The material has a rigid large plane skeleton, has multiple chemical sites for modification, and can realize efficient and narrow spectral band blue light emission of the material by simply regulating peripheral hanging groups. The thermal decomposition temperature is as high as 426.1 DEG C, and the material has good thermal stability. The maximum emission peak of photoluminescence in toluene solution is located at 458 nm, the half-width is 40 nm, the fluorescence quantum efficiency is 78.2%, the maximum emission peak of the obtained doped blue light electroluminescent device is located at 468 nm and the color coordinates are (0.15, 0.25), and the corresponding maximum external quantum efficiency (EQE) is 15.2%. The MR-TADF blue light emitting material with the innovative structure and multiple scalability has an attractive application prospect.

Description

Technical Field

[0001] This invention belongs to the field of luminescent materials technology, specifically relating to the preparation of a class of indole-indole-quinoxaline-phenazine MR-TADF blue light materials and their application in organic electroluminescent devices (OLEDs). Background Technology

[0002] Since T. Ikuta's group first reported thermally activated delayed fluorescence (TADF) materials induced by multiple resonance (MR) effect in 2016 (Advanced Materials, 2016, 28, 2777-2781), these materials have attracted extensive research in fields such as OLEDs due to their narrow-band emission, high luminescence quantum efficiency (PLQY), and small Stokes shift in solvents of different polarities.

[0003] MR-TADF material molecules typically possess planar and rigid polycyclic aromatic heterocyclic structures. Heteroatoms disrupt the electron cloud distribution of the molecule, thereby inducing multiple resonance effects between the complementary conjugation effects of heteroatoms. This induces the alternating positioning of the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) on adjacent atoms, resulting in a smaller ΔE. ST This process achieves TADF properties and generates a shallow potential energy surface, resulting in unique narrow-band emission (FWHM < 50 nm). When molecules are excited to a singlet state or radiatively transition back to the ground state, their electron cloud density undergoes short-range charge transfer (SRCT) between adjacent atoms. This special SRCT mechanism differs from the intramolecular charge transfer (ICT) mechanism of traditional DA-type TADFs; instead, it resembles a locally excited (LE) process, maintaining electron-hole overlap and allowing MR-TADF materials to achieve a larger oscillator intensity. This contributes to improving the photoluminescence quantum yield (PLQY) and radiative transition rate. Furthermore, SRCT helps eliminate the spectral fine structure of LE emission caused by highly conjugated structures, resulting in a smoother emission spectrum for MR-TADF materials and further improving the purity of the emitted color.

[0004] In 2019, Shuit-Tong Lee reported on blue OLEDs based on the MR-TADF material quinolinone [3,2,1-de]acrid-5,9-dione as the active layer, achieving a maximum external quantum efficiency of 19.4% and a full width at half maximum (FWHM) of 39 nm (Adv. Optical Mater. 2019, 1801536). In 2024, Wang Lixiang's research group used the MR-TADF material 5tCzPPm as a sensitizer and obtained a maximum external quantum efficiency of 15.6 for solution-based deep blue OLEDs, demonstrating the potential application prospects of MR-TADF materials in OLEDs. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention designs a class of organic blue light-emitting materials with narrow-band emission of MR-TADF characteristics. By utilizing the synergistic effect of narrow-band emission of MR and high-efficiency luminescence of TADF, the invention realizes the narrow-band high-efficiency luminescence of MR-TADF blue light-emitting materials and their application in organic electroluminescent diodes.

[0006] This invention provides a novel type of MR-TADF blue light emitting material, which uses indole-indolequinoxalino[3,2,1-kl]phenazine as a rigid planar framework and modifies four chemical sites with groups such as tert-butyl, toluene, N,N-diphenylamine, carbazole, 3,6-di-tert-butylcarbazole, and N,N-dimethylaniline to construct a rigid planar framework.

[0007] The present invention provides a type of MR-TADF blue light-emitting material having the structure shown in Formula I:

[0008] Formula I Wherein: each of the R units is independently selected from any one of the following formulas II:

[0009] Formula II.

[0010] The specific structures of preferred MR-TADF blue light-emitting materials are shown in Formula III. These compounds are only representative examples.

[0011] Formula III.

[0012] In a more preferred MR-TADF blue light-emitting material, the R unit is tert-butyl, with the following molecular structure, named DtBuCzN: .

[0013] The preparation steps of the MR-TADF blue light-emitting material DtBuCzN are as follows: Using 1-bromo-3,6-di-tert-butyl-9-H-ylcarbazole and 1,3-difluoro-3-nitrobenzene as starting materials, the target compound was obtained through the Ullmann reaction, nitro reduction reaction, and Buchwald-Hartwig reaction. The specific steps included the following: (1) Dissolve 3,6-di-tert-butyl-9H-carbazole, 2,6-difluoronitrobenzene, and potassium phosphate in N,N-dimethylformamide and reflux for 10-12 h. After the reaction is complete, separate and purify to obtain compound M1; the molar ratio of 3,6-di-tert-butyl-9H-carbazole, 2,6-difluoronitrobenzene, and potassium phosphate is 100-105:35-40:155-160. (2) Dissolve compound M1 in dichloromethane, add liquid bromine dropwise under ice bath, stir and react for 10-12 h. After the reaction is complete, separate and purify to obtain compound M2; the molar ratio of liquid bromine to compound M1 is 2-2.2:1. (3) Dissolve compound M2 and stannous dichloromethane in chloroform, reflux for 2 h, stop the reaction, and separate and purify to obtain compound M3; wherein the molar ratio of compound M2 to stannous dichloromethane is 1:15; (4) Dissolve the palladium catalyst tris(dibenzylacetone)dipalladium and sodium cyanide in toluene, add the xylene solution of compound M3 under N2 protection, heat to 110-120 °C and reflux for 15-16 h, separate and purify to obtain the target compound.

[0014] The present invention also provides the application of the aforementioned MR-TADF blue light-emitting material as a light-emitting layer material for organic light-emitting diodes.

[0015] The structure of the blue light emitting OLED device of the present invention is: ITO / PEDOT:PSS (30nm) / mCPCN:x wt%MR-TADF (25 nm) / TmPyPB (50 nm) / LiF (1 nm) / Al (120 nm).

[0016] In this design, ITO is indium tin oxide conductive glass, serving as both the substrate and the anode; PEDOT:PSS is the hole injection layer; mCPCN is the host material of the luminescent layer; MR-TADF is the blue light-emitting material of this invention, serving as the guest material of the luminescent layer; TmPyPB is the electron transport layer; LiF is the electron injection layer; and Al is the cathode. Where x = 1-10.

[0017] In the preferred application method, the emitting layer of the blue OLED device is prepared using the MR-TADF blue light emitting material DtBuCzN, and a blue OLED device with a maximum emission peak at 468 nm and an external quantum efficiency of up to 15.2% is obtained.

[0018] Compared to current technology, the advantages of this invention are as follows: (1) The MR-TADF blue light emitting material of the present invention has a planar polynitrogen heteroatom structure. The molecular structure of the material is innovative and has multi-site modification, which can enrich the organic MR-TADF blue light emitting material library.

[0019] (2) The organic blue light emitting material of the present invention has a significant MR-TADF effect, with high luminous efficiency and high color purity, which creates conditions for high-definition display.

[0020] (3) This type of MR-TADF blue light organic light-emitting small molecule material has high thermal stability and excellent carrier transport performance.

[0021] (4) The MR-TADF blue organic light-emitting material of the present invention can be used as a light-emitting layer material and applied to blue OLED devices. The preferred embodiment of the present invention realizes blue light emission of OLED devices and obtains excellent external quantum efficiency. Attached Figure Description

[0022] Figure 1 The image shows the 1H NMR spectrum of the compound DtBuCzN obtained in Example 1 of this invention.

[0023] Figure 2 This is the mass spectrum of compound DtBuCzN obtained in Example 1 of the present invention.

[0024] Figure 3 This is a schematic diagram of the single-crystal diffraction structure of the compound DtBuCzN obtained in Example 1 of the present invention.

[0025] Figure 4 The image shows the thermogravimetric curve of the compound DtBuCzN solid powder obtained in Example 1 of this invention.

[0026] Figure 5 The compound DtBuCzN obtained in Example 1 of this invention was prepared at 10... -5 UV-Vis absorption spectrum of toluene solution with a concentration of mol / L.

[0027] Figure 6 The compound DtBuCzN obtained in Example 1 of this invention was prepared at 10... -5 Photoluminescence spectrum of toluene solution with a concentration of mol / L.

[0028] Figure 7 The compound DtBuCzN obtained in Example 1 of this invention was prepared in toluene solution (10... -5 mol / l) at 77 K (λ) exFluorescence and phosphorescence spectra at 340 nm.

[0029] Figure 8 The compound DtBuCzN obtained in Example 1 of this invention has different polarities in 10 -5 Photoluminescence spectrum of a solution with a concentration of mol / L.

[0030] Figure 9 The compound DtBuCzN obtained in Example 1 of this invention was prepared in a deoxygenated acetonitrile solution (0.1 M) using a platinum electrode as the working electrode, a platinum wire as the counter electrode, and a silver electrode as the reference electrode. Ferrocene (Fc / Fc) + Plot the cyclic voltammetry curves obtained from the internal standard compound.

[0031] Figure 10 This is an instantaneous lifetime curve of the compound DtBuCzN prepared in Example 1 of the present invention, doped with mCP film at a mass ratio of 1 wt%.

[0032] Figure 11 This is a schematic diagram of the energy levels of an electroluminescent device fabricated using the doped light-emitting layer of compound DtBuCzN obtained in Example 1 of this invention.

[0033] Figure 12 The electroluminescence spectrum of compound DtBuCzN obtained in Example 1 of this invention is shown when it is doped into mCPCN host at a mass ratio of 1 wt%.

[0034] Figure 13 The color coordinate diagram is shown for the device fabricated by doping the compound DtBuCzN obtained in Example 1 of this invention into the mCPCN host at a mass ratio of 1 wt%.

[0035] Figure 14 The graph shows the maximum external quantum efficiency and brightness of the device fabricated by doping the compound DtBuCzN obtained in Example 1 of this invention into the mCPCN host at a mass ratio of 1 wt%. Detailed Implementation

[0036] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific details described below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0037] In this invention, the preparation methods are all conventional unless otherwise specified. The raw materials used are all available from publicly available commercial sources unless otherwise specified. Example 1

[0038] The synthesis scheme of DtBuCzN based on indole-indolequinoxalino[3,2,1-kl]phenazine is as follows, wherein all reagents such as 3,6-di-tert-butylcarbazole and 2,6-difluoronitrobenzene were purchased from Bid Pharmaceutical Reagent Co., Ltd.

[0039] Synthetic route of compound DtBuCzN Synthesis of compound M1 In a 250 mL two-necked flask, 3,6-di-tert-butyl-9H-carbazole (28.5 g, 102.0 mmol), 2,6-difluoronitrobenzene (6.0 g, 37.0 mmol), potassium phosphate (33 g, 156 mmol), and 120 mL of N,N-dimethylformamide (DMF) were added. The mixture was refluxed for 10 h. After the reaction was completed, the reaction mixture was cooled to room temperature, the organic solvent was removed by vacuum distillation, and the mixture was extracted three times with dichloromethane. The solution was dried over anhydrous magnesium sulfate, filtered, and the filtrate was concentrated by vacuum distillation. The crude product was separated by silica gel column chromatography to obtain 1.14 g of pale yellow powder M1 (11.4 g, 36.86%). 1 H NMR (400 MHz, CDCl3) δ8.10 (s, 4H), 7.85 (t, J = 8.0 Hz, 1H), 7.67 (d, J = 8.0 Hz, 2H), 7.48 (dd, J= 8.6, 1.7 Hz, 4H), 7.18 (d, J = 8.6 Hz, 4H), 1.45 (s, 36H). Synthesis of compound M2 In a 100 mL double-necked flask, M1 (6.9 g, 10.2 mmol) and 50 mL of dichloromethane were added, and liquid bromine (3.5 g, 22.4 mmol) was added dropwise under ice bath conditions. The mixture was stirred for 10 h. After the reaction was completed, the reaction mixture was cooled to room temperature, the reaction was quenched with saturated sodium thiosulfate aqueous solution, extracted three times with dichloromethane, dried over anhydrous magnesium sulfate, filtered, and the filtrate was concentrated by vacuum distillation. The crude product was separated by silica gel column chromatography to obtain yellow powder M2 (5.0 g, 58.87%). 1H NMR (400MHz, CD2Cl2) δ = 8.03 (d, J = 4.7 Hz, 4H), 7.78 – 7.71 (m, 1H), 7.64 (d, J =7.9 Hz, 2H), 7.57 (s, 2H), 7.46 (d, J = 9.9 Hz, 2H), 7.05 (d, J = 8.6 Hz, 2H), 1.36 (d, J = 2.2 Hz, 36H). Synthesis of compound M3 In a 100 mL double-necked flask, compound M2 (1.14 g, 1.364 mmol), stannous dichloroethylene (1.338 g, 20.46 mmol), and 40 mL of chloroform solution were added. The mixture was refluxed for 2 h, and the reaction was stopped. The mixture was then extracted with ethyl acetate, and the organic layer was separated and dried over anhydrous magnesium sulfate. The filtrate was concentrated by vacuum distillation to obtain an orange solid powder. The crude product was separated by silica gel column chromatography to obtain 800 mg of pale orange powder M3 (800 mg, 73.02%). 1 H NMR (400 MHz, DMSO): δ =8.32 (d, J = 17.7 Hz, 4H), 7.57 (s, 2H), 7.53 – 7.48 (m, 2H), 7.33 (d, J =2.4 Hz, 2H), 7.31 (s, 1H), 7.15 (d, J = 7.8 Hz, 1H), 7.09 (d, J = 8.6 Hz, 2H), 6.95 (s, 1H), 1.42 (d, J = 5.0 Hz, 36H). Synthesis of compound DtBuCzN In a 50 mL double-necked flask, Pd2(dba)3 (39.5 mg, 0.043 mmol), sodium hydride (44.78 mg, 1.866 mmol), and 10 mL of toluene (Tol) solution were added. Under N2 protection, 15 mL of xylene solution of compound M3 (500 mg, 0.622 mmol) was added to the reaction solution, and the mixture was heated to 110 °C and refluxed for 15 h. To remove solid impurities that are insoluble in organic solvents, the xylene solution was removed by vacuum distillation. The remaining solid was dissolved in dichloromethane. The collected organic layer was dried and the solvent was evaporated. The crude product was separated by silica gel column chromatography to obtain an orange-yellow powder DtBuCzN (318 mg, 79.39%). 1HNMR (400 MHz, CD2Cl2) δ = 8.05 (d, J = 9.2 Hz, 4H), 7.79 – 7.71 (m, 1H), 7.64(d, J = 7.7 Hz, 2H), 7.57 (s, 2H), 7.46 (d, J = 8.7 Hz, 2H), 7.05 (d, J = 8.6Hz, 2H), 1.36 (t, J = 2.0 Hz, 36H). MS(TOF-MS): m / z calcd. for C 46 H 49 N3: 643.92; [MH] + Found: 643.39. Example 2

[0040] The compound DtBuCzN from Example 1 was dissolved in CD2Cl2 reagent, and its proton NMR spectrum was measured using a 400 MHz NMR spectrometer. Figure 1 As shown. Example 3

[0041] The molecular weight of compound DtBuCzN was determined using time-of-flight mass spectrometry, and its mass spectrum is shown below. Figure 2 As shown, the theoretical molecular weight of compound DtBuCzN is 643.92, and the molecular weight obtained by mass spectrometry is 643.39. Clearly, the molecular weight of the compound is accurate. Example 4

[0042] The compound DtBuCzN from Example 1 was dissolved in chloroform as a good solvent and ethanol as a poor solvent. Single crystals of DBuCzN were grown at room temperature using a solvent diffusion method, and their exact geometry was then determined by single-crystal X-ray diffraction (XRD). Figure 3 As shown. Example 5

[0043] The thermal stability of the compound DtBuCzN obtained in Example 1 was tested. Thermogravimetric analysis was performed by heating from room temperature to 700 °C at a heating rate of 20 °C / min under a nitrogen atmosphere. Figure 4 As shown, the compound DtBuCzN loses 5% of its weight at 425.5 °C, indicating that the material has good thermal stability, which lays the foundation for its subsequent use as a light-emitting layer in solution processing and the fabrication of fully vapor-deposited devices. Example 6

[0044] The compound DtBuCzN from Example 1 was dissolved in a toluene solution (10). -5The UV-Vis absorption spectrum of compound DtBuCzN in toluene solution at room temperature was measured (M). Figure 5 It can be seen that the strong absorption band in the 280 nm to 300 nm range originates from the π-π* transition within the molecule, and shows a strong and sharp absorption peak at 436 nm, which is attributed to the short-range charge transfer transition absorption of the entire rigid molecular structure. Example 7

[0045] The compound DtBuCzN from Example 1 was dissolved in a toluene solution (10). -5 The photoluminescence spectrum of compound DtBuCzN in toluene solution at room temperature was measured (M). Figure 6 It can be seen that the compound exhibits a strong and sharp emission peak at 458 nm, which is blue light emission, and its full width at half maximum (FWHM) is 40 nm. Example 8

[0046] The compound DtBuCzN from Example 1 was fabricated into a thin film on a glass substrate. The fluorescence spectrum (Fl) and phosphorescence spectrum (Ph) of the compound DtBuCzN in its pure film state at 77 K were tested. Figure 7 As shown, both the low-temperature fluorescence and low-temperature phosphorescence spectra exhibit broad peaks without fine structure, indicating that they are generated by intramolecular charge transfer. Based on the peak positions of the low-temperature fluorescence and phosphorescence spectra and the formula E = 1240 / λ, the S1 and T1 energy levels of the compound DtBuCzN can be estimated to be 2.84 eV and 2.48 eV, respectively, with ΔE... ST It is 0.36 eV. Example 9

[0047] The compound DtBuCzN from Example 1 was dissolved in n-hexane, toluene, diethyl ether, dioxane, tetrahydrofuran, dichloromethane, acetone, N,N-dimethylformamide, and ethyl acetate solutions, respectively (10 ppm). -5 M), and tested its photoluminescence spectra in different solutions, such as Figure 8 As shown, the compounds exhibited similar emission spectra. With increasing solvent polarity, all compounds showed a weak solvation effect and a negligible Stokes shift, which is a typical characteristic of thermally active delayed fluorescence (MR-TADF) compounds with multiple resonance effects. Example 10

[0048] The electrochemical performance testing conditions for compound DtBuCzN in Example 1 were as follows: The prepared compound DtBuCzN was placed in a deoxygenated acetonitrile solution (0.1 M), with a platinum electrode as the working electrode, a platinum wire as the counter electrode, and a silver electrode as the reference electrode. Ferrocene (Fc / Fc) was used as the reference electrode. + (The compound is used as an internal standard for testing.) Figure 9 As shown, compound DtBuCzN exhibits an irreversible oxidation peak in the 0-0.7 V range. Based on empirical formulas, the HOMO level of the compound can be calculated to be -4.69 eV. Combining this with the peak position of the blue-outer absorption spectrum of the pure film, the band gap (E0) of the compound can be calculated. g The value is 2.75 eV, and its LUMO is calculated to be -1.94 eV. Example 11

[0049] The photoluminescence quantum efficiency (PLQY) of compound DtBuCzN in Example 1 was tested in a transient fluorometer equipped with an integrating sphere. The test method is as follows: the compound was made into a 0.1 wt% mCP doped sample film. The fluorescence intensity of the blank quartz plate and the sample film were tested successively. The fluorescence quantum efficiency (PLQY) of the compound was calculated to be 78.2%. Example 12

[0050] The compound DtBuCzN from Example 1 was tested in a nitrogen atmosphere in a 0.1% doped mCP film, and its transient lifetime was measured using an FlS1000. Figure 10 As shown, the retardation lifetime of compound DtBuCzN was found to be 31.4 µs after fitting. The ΔE of the material was obtained based on the full width at half maximum (FWHM) of 40 nm in Example 7 and the test results in Example 8. ST The value of 0.36 eV indicates that the compound DtBuCzN has MR-TADF properties. Example 13

[0051] Application of compound DtBuCzN in Example 1 in organic electroluminescent devices. Using the compound as the guest material for the emitting layer, an organic electroluminescent diode with the structure ITO / PEDOT:PSS (30 nm) / mCPCN:compound DtBuCzN (25 nm) / TmPyPB (50 nm) / LiF (1 nm) / Al (120 nm) was fabricated. In this structure, PEDOT:PSS is the hole injection layer, mCPCN is the host material for the emitting layer, TmPyPB is the electron transport layer, LiF is the electron injection layer, and Al is the cathode. Figure 11 As shown. Example 14

[0052] The electroluminescence spectrum of compound DtBuCzN in Example 1 in an organic electroluminescent device is as follows: Figure 12 As shown, at a doping concentration of 1 wt%, the electroluminescent device exhibits blue light emission, with the maximum emission peak of the doped device located at 468 nm. Example 15

[0053] The color coordinates of the electroluminescent device of compound DtBuCzN in Example 1 at a doping concentration of 1 wt% are as follows: Figure 13 As shown, the corresponding color coordinates are (0.15, 0.25). Example 16

[0054] The external quantum-luminescence curve of compound DtBuCzN in Example 1 in an organic electroluminescent device is shown below. Figure 14 As shown, at a doping concentration of 1 wt%, the maximum external quantum efficiency of its doped device is 15.2%.

[0055] Although the invention has been described in conjunction with preferred embodiments, the invention is not limited to the above embodiments, and it should be understood that the appended claims summarize the scope of the invention. Guided by the inventive concept, those skilled in the art should recognize that any modifications made to the various embodiments of the invention will be covered by the spirit and scope of the claims.

Claims

1. A class of indole-indole-quinoxalinophenazine MR-TADF blue light-emitting materials, characterized in that, The blue light material has the molecular structure shown in Formula I: ， Formula I Wherein: the R unit is tert-butyl.

2. The preparation method of the indole-indole-quinoxaline-phenazine MR-TADF blue light material as described in claim 1, characterized in that: Includes the following steps: (1) Dissolve 3,6-di-tert-butyl-9H-carbazole, 2,6-difluoronitrobenzene, and potassium phosphate in N,N-dimethylformamide and reflux for 10-12 h. After the reaction is complete, separate and purify to obtain compound M1; the molar ratio of 3,6-di-tert-butyl-9H-carbazole, 2,6-difluoronitrobenzene, and potassium phosphate is 100-105:35-40:155-160. (2) Dissolve compound M1 in dichloromethane, add liquid bromine dropwise under ice bath, stir and react for 10-12 h. After the reaction is complete, separate and purify to obtain compound M2; the molar ratio of liquid bromine to compound M1 is 2-2.2:

1. (3) Dissolve compound M2 and stannous dichloromethane in chloroform, reflux for 2 h, stop the reaction, and separate and purify to obtain compound M3; wherein the molar ratio of compound M2 to stannous dichloromethane is 1:15; (4) Dissolve the palladium catalyst and sodium cyanide in toluene, add the xylene solution of compound M3 under N2 protection, heat to 110-120 °C and reflux for 15-16 h, separate and purify to obtain the target compound; the palladium catalyst is tris(dibenzylacetone)dipalladium; 。 3. The application of the indole-indole-quinoxaline-phenazine MR-TADF blue light material as described in claim 1, characterized in that: The MR-TADF blue light material is used as a blue light-emitting material in the light-emitting layer of organic electroluminescent devices.

4. The application of the indole-indolequinoxaline-phenazine MR-TADF blue light material as described in claim 3, characterized in that: The MR-TADF blue light material serves as the guest material for the light-emitting layer in organic electroluminescent devices.

5. The application of the indole-indole-quinoxaline-phenazine MR-TADF blue light material as described in claim 4, characterized in that: The doping amount of the MR-TADF blue light material is 1-10 wt%.

6. The application of the indole-indole-quinoxaline-phenazine MR-TADF blue light material as described in claim 3, characterized in that: The structure of the organic electroluminescent device is ITO / PEDOT:PSS / mCPCN:x wt%MR-TADF / TmPyPB / LiF / Al; wherein, ITO is indium tin oxide conductive glass, serving as the substrate and anode; PEDOT:PSS is the hole injection layer; mCPCN is the main material of the light-emitting layer; MR-TADF is the indole-indole-quinoxaline-phenazine MR-TADF blue light material as described in claim 1; TmPyPB is the electron transport layer; LiF is the electron injection layer; and Al is the cathode; x = 1~10.

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