Applications of low-temperature, short-time thermal cross-linking materials as hole transport materials, hole transport layers, and PhOLED devices

Abstract

This invention discloses the application of a low-temperature, short-time thermally crosslinkable material as a hole transport material, a hole transport layer, and a PhOLED device. The hole transport material can be VBPhCz and / or VBTPA. This material has a low crosslinking temperature, a short crosslinking time, and good thermal stability. It can prepare a hole transport layer with good resistance to solvent erosion under mild conditions, avoiding device aging caused by prolonged high-temperature testing. Simultaneously, the hole transport layer obtained after thermal crosslinking has stable photophysical properties. When applied to PhOLED devices, the resulting devices exhibit good stability and excellent performance. Furthermore, it enables the solution-based fabrication of green PhOLED devices, including a multifunctional layer with an emitting layer, thus promoting the industrialization of solution-based green PhOLED device fabrication.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronic functional materials and devices, and relates to the application of a low-temperature, short-time thermal cross-linking material as a hole transport material, a hole transport layer, and a PhOLED device. Background Technology

[0002] Solution-based organic light-emitting diodes (OLEDs) offer advantages such as low cost and the ability to be mass-produced over large areas, making them a crucial direction for the future development of organic phosphorescent light-emitting diodes (PhOLEDs). PhOLEDs with multiple functional layers can help achieve high device performance; however, due to the erosion issues between the upper and lower layers, the fabrication of multilayer devices using low-cost solution methods still faces significant challenges, particularly the solution-based fabrication of the emissive layer. This is because multilayer devices typically include hole injection / hole transport layers (HIL / HTL), electron blocking layers, emissive layers (EML), hole blocking layers, and electron transport / electron injection layers (ETL / EIL). To achieve solution-based fabrication of the emissive layer, a hole transport layer with good erosion resistance is essential. Currently, there are two main solutions: using orthogonal solvents between the upper and lower functional layers or using solvent-resistant crosslinking materials. However, due to the solubility limitations of orthogonal solvents, the design and synthesis of crosslinked hole transport materials become more necessary and urgent.

[0003] Styrene groups do not require initiators during crosslinking and do not generate other small molecules that adversely affect the device, making them ideal crosslinking groups. Crosslinking technology can give materials good solvent resistance, but most previously reported styrene-based thermally crosslinked materials have actual heat treatment temperatures as high as 200°C and times exceeding one hour. Prolonged high-temperature testing can cause device aging and affect device performance. This has a significant impact on the selection of substrate materials in multifunctional layer devices, the application scenarios of materials, and the overall thermal stability of devices. Therefore, designing and synthesizing styrene-based hole transport materials that can be thermally crosslinked at low temperatures for short times is of great significance for the solution-based fabrication of PhOLED light-emitting devices with multifunctional layer stacking. Summary of the Invention

[0004] The purpose of this invention is to provide an application of a low-temperature, short-time thermal crosslinking material as a hole transport material, a hole transport layer, and a PhOLED device. This material, as a hole transport material, exhibits low crosslinking temperature, fast crosslinking speed, and good stability, avoiding aging caused by prolonged high temperatures. It also possesses excellent resistance to solvent corrosion. When applied to PhOLED light-emitting devices, it results in good device stability and superior performance. Furthermore, it enables solution-based fabrication of the hole transport layer and light-emitting layer, effectively reducing fabrication costs, delaying device aging, and achieving high-efficiency device performance.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A low-temperature, short-time thermal cross-linking material is provided for use as a hole transport material, the structural formula of which is shown in Formula I:

[0007]

[0008] Where R is an electron-donating group, and

[0009] When R is When it is, it is 9-(4'-vinyl-[1,1'-diphenyl]-4-yl)-3-(4-styryl)-9H-carbazole (denoted as VBPhCz).

[0010] When R is When it is 4,4'-bis(4-vinylphenyl)triphenylamine (denoted as VBTPA).

[0011] According to the above scheme, the hole transport material is VBPhCz and / or VBTPA.

[0012] A method for preparing the above-mentioned low-temperature, short-time thermal crosslinking material is provided, comprising the following steps:

[0013] Under inert gas protection, 3-bromo-9-(4-bromophenyl)carbazole or bis(4-bromophenyl)aniline, 4-vinylphenylboronic acid and catalyst are stirred and heated to 100-110°C in a mixed solution of tetrahydrofuran and potassium carbonate aqueous solution to carry out a coupling reaction to obtain a material that can be thermally crosslinked at low temperature for a short time.

[0014] According to the above scheme, the molar ratio of 3-bromo-9-(4-bromophenyl)carbazole or bis(4-bromophenyl)aniline to 4-vinylphenylboronic acid is 2:4 to 2:5.

[0015] According to the above scheme, the catalyst is Pd(PPh3)4.

[0016] According to the above scheme, the amount of catalyst added is 6-8% of the molar amount of 3-bromo-9-(4-bromophenyl)carbazole or bis(4-bromophenyl)aniline.

[0017] According to the above scheme, the reflux time is 48-56 hours.

[0018] According to the above scheme, the concentration of the potassium carbonate aqueous solution is 1.8-2.2 mol / L; the volume ratio of the tetrahydrofuran to the potassium carbonate aqueous solution is 5:2 to 7:2.

[0019] A hole transport layer is provided, which is prepared from the above-mentioned material that can be thermally crosslinked at low temperature for a short time.

[0020] According to the above scheme, the hole transport layer is prepared by a solution method. The solution method involves preparing a solution of a low-temperature, short-time thermal cross-linking material and coating it onto a substrate to form a hole transport layer.

[0021] Preferably, the solution method is spin coating.

[0022] Preferably, it is prepared by spin coating using tetrahydrofuran and 1,2-dichloroethane as solvents.

[0023] According to the above scheme, the hole transport material is cross-linked at 130-175℃ for 18-22 minutes to prepare the hole transport layer.

[0024] According to the above scheme, the hole transport layer is prepared by vacuum evaporation process.

[0025] An application of the aforementioned hole transport layer in PhOLED is provided.

[0026] A PhOLED device is provided, comprising a substrate, a hole injection layer (HIL), a hole transport layer (HTL), an emissive layer (EML), an electron transport layer (ETL), an electron injection layer (EIL), and electrodes.

[0027] According to the above scheme, the hole injection layer has a thickness of 30-40nm; the hole transport layer has a thickness of 20-30nm; the light emission layer has a thickness of 30-75nm; the electron transport layer has a thickness of 45-55nm; and the electron injection layer has a thickness of 1.8-2.2nm.

[0028] According to the above scheme, the hole injection layer and the hole transport layer are prepared by solution method; the light-emitting layer is prepared by solution method or vacuum evaporation process.

[0029] Preferably, the solution method is a spin coating process.

[0030] According to the above scheme, the hole injection layer is poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS, CLEVIOS P VP AI4083); the light-emitting layer is based on 4,4'-bis(9-carbazole)biphenyl (CBP) and doped with green light-emitting material Ir(L)2(acac-Cz) or Ir(ppy)3, preferably, the doping ratio of Ir(L)2(acac-Cz) is 14-16wt%, and the doping ratio of Ir(ppy)3 is 9-11wt%; the electron transport layer is 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI); the electron injection layer is lithium 8-hydroxyquinoline (Liq); and the electrode is an Al electrode.

[0031] A method for fabricating the above-mentioned PhOLED device is provided, comprising the following steps:

[0032] 1) Clean and pre-treat the indium tin oxide semiconductor transparent conductive film (ITO) glass;

[0033] 2) A hole injection layer is prepared on the ITO surface obtained in step 1) by spin coating;

[0034] 3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating;

[0035] 4) A light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by spin coating or vacuum evaporation.

[0036] 5) ETL, EIL and electrodes are sequentially prepared on the surface of the light-emitting layer obtained in step 4) by vacuum evaporation process to obtain the PhOLED device.

[0037] According to the above scheme, in step 1), the ITO glass is ultrasonically cleaned with acetone and isopropanol for 10 minutes each, rinsed with ultrapure water, dried with nitrogen, and then treated with oxygen plasma for 3-5 minutes.

[0038] According to the above scheme, in step 2), the spin coating process conditions are as follows: spin coating in air at a speed of 2500-3500 rpm for 55-60 seconds, and then annealing in a glove box at 120-130℃ for 10-15 minutes.

[0039] According to the above scheme, in step 3), tetrahydrofuran and 1,2-dichloroethane are used as solvents, and VBPhCz and / or VBTPA are used as hole transport materials.

[0040] Preferably, the concentration of the hole transport material is 3-5 mg / mL.

[0041] Preferably, when VBPhCz and VBTPA are used simultaneously, the mass ratio is 4:5 to 5:4.

[0042] According to the above scheme, in step 3), the spin coating process conditions are as follows: spin coating at 2000-2500 rpm for 55-60 seconds, annealing at 100-110℃ for 10-15 minutes, and then crosslinking at 130-175℃ for 18-22 minutes.

[0043] According to the above scheme, in step 4), the spin coating process conditions are: spin coating at 4000-4500 rpm for 55-60 seconds, followed by annealing at 55-60°C for 30-35 minutes. Preferably, the concentration of CBP in the spin coating is 10-12 mg / mL.

[0044] According to the above scheme, in step 5), the ETL, EIL, and Al electrodes are finally deposited by vapor deposition using an OLED-V type (Shenyang Vacuum Research Institute) organic multifunctional coating machine, and the vacuum level is reduced to 5×10⁻⁶. -4 At Pa, TPBI is used as ETL, Liq as EIL, and Al as cathode, and the material is obtained by sequentially vapor deposition on ITO / HIL / HTL / EML.

[0045] The beneficial effects of this invention are as follows:

[0046] 1. This invention provides an application of a low-temperature, short-time thermally crosslinkable material as a hole transport material. This material exhibits a low crosslinking temperature (<180°C), a short crosslinking time (~20 min), and good thermal stability (thermal decomposition temperature T). d >446°C) can be used to prepare hole transport layers with good resistance to solvent erosion under mild conditions, avoiding device aging caused by long-term high temperature testing. At the same time, the hole transport layer obtained after thermal crosslinking has stable photophysical properties. When the hole transport layer is applied to PhOLED devices, the resulting devices have good stability and excellent performance.

[0047] 2. This invention also realizes a green PhOLED device fabricated by a solution method with a multifunctional layer including the emitting layer, with a device start-up voltage of 6.1V and a maximum brightness of 8271 cd / m². 2 With a maximum current efficiency of 12.4 cd / A, it achieved device performance comparable to that of green PhOLED devices with vacuum-deposited light-emitting layers, thus promoting the industrialization of solution-based green PhOLED device fabrication. Attached Figure Description

[0048] Figure 1 Thermogravimetric analysis of VBPhCz prepared in Example 1 and VBTPA prepared in Example 2 ( Figure 1 a) and differential scanning calorimetry ( Figure 1 b,c).

[0049] Figure 2 These are cyclic voltammograms of VBPhCz (top figure) prepared in Example 1 and VBTPA (bottom figure) prepared in Example 2.

[0050] Figure 3 The VBPhCz obtained in Example 1 is in solution (a, DCM, 1×10⁻⁶). -5 M), UV absorption spectra of the films before and after crosslinking (b), and photoluminescence spectra at room temperature (c).

[0051] Figure 4 The VBTPA prepared in Example 2 is in solution (a, DCM, 1×10⁻⁶). -5M), UV absorption spectra of the films before and after crosslinking (b), and photoluminescence spectra at room temperature (c).

[0052] Figure 5 The UV absorption spectra of the VBPhCz films prepared in Example 1 after crosslinking for 20 min (a), 40 min (b), and 60 min (c) are washed with different solvents.

[0053] Figure 6 The images show the UV absorption spectra of the VBTPA films prepared in Example 2 after crosslinking for 20 min (a), 40 min (b), and 60 min (c) and then washing them with different solvents.

[0054] Figure 7 The diagram shows the device structure (left) and the energy level structure (right) of the related materials after spin coating of the light-emitting layer using the solution method in the embodiments.

[0055] Figure 8 The figures show the brightness-voltage-current density curves (a), power efficiency-voltage-current efficiency curves (b), and electroluminescence spectrum at maximum brightness (c) for the device structure ITO / PEDOT:PSS (35nm) / HTL (20nm) / CBP:Ir(ppy)3 (30nm, 10wt%) / TPBI (50nm) / Liq (2nm) / Al. The HTLs are VBTPA (circular), VBTPA&VBPhCz (triangular), or VBPhCz (square), fabricated by EML vacuum evaporation.

[0056] Figure 9 The images show the brightness-voltage-current density curves (a), power efficiency-voltage-current efficiency curves (b), and electroluminescence spectrum (c) at maximum brightness for the device structure: ITO / PEDOT:PSS (35nm) / HTL (30nm) / CBP:Ir(L)2(acac-Cz) (70nm, 15wt%) / TPBI (50nm) / Liq (2nm) / Al. The HTLs are VBTPA (circular), VBTPA / VBPhCz (triangular), or VBPhCz (square), prepared by EML solution spin-coating.

[0057] Figure 10 The low-temperature phosphorescence spectra (77K) of VBPhCz (a) and VBTPA (b) are obtained in solvent 2MeTHF. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0059] Example 1: Synthesis of hole transport material VBPhCz

[0060]

[0061] 3-Bromo-9-(4-bromophenyl)carbazole (3.00 g, 7.48 mmol), 4-vinylphenylboronic acid (2.77 g, 18.70 mmol), Pd(PPh3)4 (0.61 g, 0.52 mmol), and 60 mL of potassium carbonate aqueous solution (2 mol / L) were weighed into a 500 mL double-necked flask. 180 mL of tetrahydrofuran was added, and the mixture was stirred and heated to 100 °C under nitrogen protection. After stirring and reflux for 48 h, the mixture was allowed to cool naturally to room temperature and filtered under reduced pressure. The filter cake was washed with ethyl acetate. The filtrate was extracted with water and ethyl acetate, and the organic phase was collected, dried over anhydrous sodium sulfate, and rotary evaporated under reduced pressure to obtain a solid powder. The solid powder was separated by column chromatography using dichloromethane / n-hexane (1:10) as the eluent. VBPhCz (2.54 g) was obtained after separation, with a yield of 76%.

[0062] 1 H NMR (400MHz, CDCl3) δppm: 8.40-8.35(m,1H),8.23-8.18(m,1H),7.88-7.81(m,2H),7.74-7. 63(m,7H),7.59-7.41(m,7H),7.33(ddd,1H),6.80(ddd,2H),5.83(ddd,2H),5.30(ddd,2H). 13 C NMR (100MHz, CDCl3) δppm:141.50,141.44,140.49,139.99,139.66,137.15,136.95,136.67,136.44,136.06,133.20,128.47,127.48,127.39, 127.35,126.98,126.84,126.35,125.48,124.14,123.69,120.55,120. 33,118.78,114.39,113.65,110.26,110.15,29.86.MS(ESI,m / z)[M+H] + calcd for C34 H 25 N:447.1987; found:448.2082.

[0063] Example 2: Synthesis of hole transport material VBTPA

[0064]

[0065] Bis(4-bromophenyl)aniline (2.00 g, 4.96 mmol), 4-vinylphenylboronic acid (1.84 g, 12.40 mmol), Pd(PPh3)4 (0.40 g, 0.35 mmol), and 50 mL of potassium carbonate aqueous solution (2 mol / L) were weighed into a 500 mL double-necked flask. 150 mL of tetrahydrofuran was added, and the mixture was stirred and heated to 100 °C under nitrogen protection. After stirring and reflux for 48 h, the mixture was allowed to cool naturally to room temperature and filtered under reduced pressure. The filter cake was washed with ethyl acetate. The filtrate was extracted with water and ethyl acetate, and the organic phase was collected, dried over anhydrous sodium sulfate, and rotary evaporated under reduced pressure to obtain a solid powder. The solid powder was separated by column chromatography using n-hexane as the eluent. VBTPA (1.99 g) was obtained after separation, with a yield of 89%.

[0066] 1 H NMR (400MHz, CDCl3) δppm: 7.59-7.44(m,12H),7.33-7.27(m,2H),7.19(d,6H),7.07(t,1H),6.76(dd,2H),5.79(d,2H),5.28(t,2H). 13 C NMR (100MHz, CDCl3) δppm:147.61,147.18,140.12,136.59,136.33,135.02, 129.52,127.79,126.84,124.86,124.31,123.40,113.79.MS(ESI,m / z)[M+H] + calcd for C 34 H 27 N:449.2143; found:450.2218.

[0067] The following are performance tests of VBPhCz prepared in Example 1 and VBTPA prepared in Example 2.

[0068] 1) Thermogravimetric analysis and differential scanning calorimetry of VBPhCz and VBTPA

[0069] Thermogravimetric analysis of VBPhCz and VBTPA showed that, with a mass loss of 5 wt%, the decomposition temperatures (T0) of VBPhCz and VBTPA were... dThe temperatures were 462.7℃ and 446.0℃ respectively. Figure 1 a, Table 1), and its differential scanning calorimetry analysis showed that the first scan of VBPhCz exhibited a broad and strong exothermic peak in the range of 138-200℃, with a peak temperature of 150℃. Figure 1 b); while VBTPA exhibits a relatively narrow exothermic peak between 172-201℃, with a peak temperature of 175℃. Figure 1 c), from which it can be deduced that the optimal crosslinking temperatures for VBPhCz and VBTPA are 150℃ and 175℃, respectively (Table 1). No other thermal effects were found in the second differential scan. Figure 1 b, c) demonstrate the good thermal stability of VBPhCz and VBTPA before and after crosslinking.

[0070] 2) Cyclic voltammetric analysis of VBPhCz and VBTPA

[0071] Cyclic voltammetry analysis of VBPhCz and VBTPA was performed using an electrochemical workstation with a three-electrode configuration in one chamber. The working electrode was a platinum disk electrode, the auxiliary electrode was a platinum wire electrode, and the standard electrode was a silver electrode. The standard was ferrocene, and the electrolyte was tetrabutylammonium hexafluorophosphate (TBAPF6, 0.1 M). The entire test was conducted under nitrogen protection using dichloromethane (10... -3 The oxidation was carried out in a solution of M) at a scan rate of 100 mV / s. The oxidation voltages of VBPhCz and VBTPA were measured to be 1.21 V and 1.06 V, respectively. Figure 2 ), calculated (Table 1, HOMO = -(E) ox,onset -E Fc / Fc+ +4.8eV), LUMO = HOMO - E g E g =1240 / λ, λ from dichloromethane of VBPhCz and VBTPA (10 -5 The HOMO energy levels of the two materials (VBPhCz and VBTPA) were obtained from the UV absorption spectra of the solutions (mol / mL). The HOMO energy levels of the two materials were -5.43 eV and -5.58 eV, respectively, while the HOMO energy level of the hole injection layer (PEDOT:PSS) was -5.2 eV. This indicates that the hole transport materials VBPhCz and VBTPA have small hole injection energy barriers, which is beneficial for constructing energy level matched PhOLED devices.

[0072] Table 1. Thermal stability, electrochemical properties, and photophysical properties of hole transport materials VBPhCz and VBTPA

[0073]

[0074] 3) Photophysical properties of VBPhCz and VBTPA

[0075] The UV-Vis absorption spectra of the hole transport material VBPhCz in solution and thin film show ( Figure 3 (a, b) VBPhCz exhibits two absorption peaks in both solution and film states. The absorption at ~300 nm is attributed to the n-π* transition of phenylcarbazole, while the absorption at ~330 nm originates from the π-π* transition of phenylcarbazole. This is similar to what has been reported in the literature. Furthermore, the absorption and photoluminescence spectra of VBPhCz before and after crosslinking show good overlap. Figure 3 c) Furthermore, crosslinking VBPhCz at different times revealed almost no change in its spectral properties, indicating that the crosslinking of the styrene groups in the VBPhCz molecular structure has almost no effect on the photophysical properties of phenylcarbazole.

[0076] During the experiment, it was found that VBTPA exhibited significant crystallization during spin-coating, but after cross-linking, the crystallization disappeared, forming an amorphous film. UV-Vis absorption spectroscopy studies of VBTPA in solution and film revealed (…). Figure 4 a) Before crosslinking, the π-π* transition absorption of VBTPA film was at 384 nm, while after crosslinking, the UV absorption showed a blue shift of 35 nm, consistent with its UV absorption in solution. Furthermore, the photoluminescence of VBTPA after crosslinking also showed a red shift of 14 nm. Figure 4 c) Therefore, it can be inferred that the difference in photophysical properties of VBTPA before and after crosslinking originates from the crystallization of VBTPA before crosslinking. The crystalline state causes the ordered arrangement of the film before crosslinking to tend towards a high-energy unstable state, allowing it to be excited at longer wavelengths to produce shorter wavelength light. Furthermore, treatment of VBTPA with different crosslinking times revealed good overlap between its absorption and emission spectra. Figure 4 Therefore, crosslinking is beneficial for forming a more stable amorphous film. The difference in photophysical properties before and after crosslinking also indicates that the molecular structure of VBTPA is relatively weak before crosslinking. However, the photophysical properties of the styrene group remain consistent after crosslinking at different times, indicating that VBTPA forms a more rigid polymer after crosslinking due to the polymerization reaction. The photophysical properties of the hole transport core group—triphenylamine group—remain stable. VBTPA can be prepared by thermal crosslinking solution method for hole transport layers in PhOLED devices.

[0077] 4) Solvent resistance of VBPhCz and VBTPA

[0078] To fabricate OLED devices with multifunctional layers via solution processing, the hole transport layer must possess excellent solvent resistance. Therefore, the resistance of VBPhCz and VBTPA films to corrosion by different solvents after crosslinking for 20 min, 40 min, and 60 min, respectively, was investigated using simple UV-Vis absorption spectroscopy. The VBPhCz films crosslinked for different times were then cleaned with chlorobenzene, 1,2-dichloroethane, and tetrahydrofuran, respectively. Figure 5 It was found that the absorption intensity of the films increased slightly after cleaning. However, the spectra of films cleaned with different solvents at the same crosslinking time showed good overlap, and the absorption spectra after cleaning with longer crosslinking times remained almost unchanged. This indicates that VBPhCz has fully reacted after 20 minutes of crosslinking, and the increase in absorption intensity is likely due to the removal of small impurities in the film, resulting in more efficient absorption. Therefore, VBPhCz exhibits good solvent resistance after 20 minutes of crosslinking.

[0079] Films of VBTPA crosslinked at 175℃ for 20 min, 40 min, and 60 min were cleaned with chlorobenzene, 1,2-dichloroethane, and tetrahydrofuran, respectively. It was found that after 20 min of crosslinking... Figure 6 a) The UV absorption spectra of the VBTPA film after cleaning with different solvents showed good overlap at 258 nm compared to before cleaning. However, the absorption intensity at 349 nm decreased to 92% of that before cleaning, and the corresponding peak position also showed a slight blue shift. Despite this, the UV absorption spectra of the films after cleaning with different solvents showed good overlap. We speculate that this may be due to the relatively low rigidity of the triphenylamine as the central group in the molecule. Although VBTPA has reacted sufficiently after 20 min of crosslinking and exhibits good solvent resistance, the resulting polymer network structure has relatively low rigidity. Cleaning with different solvents does not dissolve the crosslinked polymer structure, but it does alter the stacking pattern between the triphenylamine groups to some extent, thus causing the difference in absorption intensity and wavelength at 349 nm before and after cleaning. Furthermore, when crosslinking for 40 min, the absorption of the films before and after cleaning with different solvents showed good overlap. Figure 6 b), but the absorption peak at 349 nm still shows a slight blue shift; even after 60 min of crosslinking ( Figure 6c) The UV absorption spectrum intensity of the film after cleaning with chlorobenzene and tetrahydrofuran increased compared to before cleaning, indicating that longer crosslinking time led to more complete polymerization of VBTPA, resulting in a denser film and further enhanced rigidity of the polymer network structure. Based on the differences in solvent resistance of VBTPA in different solvents, it can be concluded that VBTPA exhibits good solvent resistance after 20 minutes of crosslinking and maintains the same degree of solvent resistance to different solvents. VBPhCz and VBTPA can be prepared by a thermally crosslinked solution method for stacking in PhOLED multifunctional layers.

[0080] 5) Liquid low-temperature phosphorescence spectra of VBPhCz and VBTPA

[0081] Based on the liquid low-temperature phosphorescence spectra of VBPhCz and VBTPA ( Figure 10 The triplet energy levels of VBPhCz and VBTPA can be calculated to be 2.66 eV and 2.27 eV, respectively. The lower triplet energy of VBTPA cannot effectively block excitons, and the triplet state and its quenching result in a greater efficiency roll-off. With the addition of VBPhCz, which has a stronger rigid structure and a higher triplet energy level, the device achieves a lower efficiency roll-off and more stable device performance.

[0082] Example 3

[0083] A PhOLED device based on VBPhCz as a thermally crosslinked HTL is provided, constructing an ITO / PEDOT:PSS (35nm) / VBPhCz (30nm) / CBP:Ir(L)2(acac-Cz) (70nm, 15wt%) / TPBI (50nm) / Liq (2nm) / Al device structure, wherein the light-emitting layer CBP:Ir(L)2(acac-Cz) is prepared by solution spin-coating, including the following steps:

[0084] (1) First, the indium tin oxide semiconductor transparent conductive film (ITO) glass was ultrasonically cleaned with acetone and isopropanol for 10 minutes each, then rinsed with ultrapure water, dried with nitrogen, and then treated with oxygen plasma for 3 minutes.

[0085] (2) A hole injection layer was prepared on the ITO surface obtained in step 1) by spin coating process. Specifically, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS, CLEVIOS P VP AI4083) was used as the hole injection layer and spin-coated in air at 3000 rpm for 60 s. Then, it was placed in a glove box and annealed at 120°C for 10 minutes with a thickness of 35 nm.

[0086] (3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating process; specifically: in a glove box, tetrahydrofuran and 1,2-dichloroethane with a volume ratio of 1:1 are used as solvents, VBPhCz is used as hole transport material with a concentration of 5mg / mL, and spin-coated on the ITO / PEDOT:PSS substrate at 2000rpm for 60s. After annealing at 100℃ for 10 minutes, the hole transport layer is crosslinked at 150℃ for 20 minutes, and the film thickness is 30nm.

[0087] (4) The light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by spin coating process. Specifically, in a glove box, chloroform is used as solvent, and 4,4'-bis(9-carbazole)biphenyl (CBP) is used as the host material and doped with 15wt% green light-emitting material Ir(L)2(acac-Cz) as the light-emitting layer. The concentration of CBP is 10mg / mL. The coating is spin-coated on an ITO / PEDOT:PSS / HTL substrate at 4000rpm for 60s, annealed at 55℃ for 30 minutes, and the thickness is 70nm.

[0088] (5) Finally, ETL, EIL, and Al electrodes were deposited by vapor deposition using an OLED-V type (Shenyang Vacuum Research Institute) organic multifunctional coating machine, with the vacuum level set to 5×10⁻⁶. -4 At Pa, 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI) was used as ETL, and TPBI (50 nm) / Liq (2 nm) / Al were sequentially deposited on ITO / HIL / EML.

[0089] The structural formulas of CBP, TPBI, and Ir(L)2(acac-Cz) are shown below:

[0090]

[0091] Example 4

[0092] A PhOLED device based on VBPhCz as a thermally crosslinked HTL is provided, constructing an ITO / PEDOT:PSS (35nm) / VBPhCz (20nm) / CBP:Ir(ppy)3 (30nm, 10wt%) / TPBI (50nm) / Liq (2nm) / Al device structure, wherein the light-emitting layer CBP:Ir(ppy)3 is prepared by vacuum evaporation, including the following steps:

[0093] (1) Same as Example 3.

[0094] (2) Same as Example 3.

[0095] (3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating process; specifically: in a glove box, tetrahydrofuran and 1,2-dichloroethane with a volume ratio of 1:1 are used as solvents, VBPhCz is used as hole transport material with a concentration of 3mg / mL, and spin-coated on the ITO / PEDOT:PSS substrate at 2000rpm for 60s. After annealing at 100℃ for 10 minutes, the hole transport layer is crosslinked at 150℃ for 20 minutes, and the film thickness is 20nm.

[0096] (4) The light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by vacuum evaporation process. Specifically, CBP is used as the main material and doped with 10wt% green light-emitting material Ir(ppy)3. It is vacuum evaporated onto the substrate of ITO / PEDOT:PSS / HTL as the light-emitting layer with a thickness of 30nm.

[0097] Where: the structural formula of Ir(ppy)3 is

[0098] (5) Same as Example 3.

[0099] Example 5

[0100] A PhOLED device based on VBTPA as a thermally crosslinked HTL is provided, constructing an ITO / PEDOT:PSS (35nm) / VBTPA (30nm) / CBP:Ir(L)2(acac-Cz) (70nm, 15wt%) / TPBI (50nm) / Liq (2nm) / Al device structure, wherein the light-emitting layer CBP:Ir(L)2(acac-Cz) is prepared by solution spin-coating, including the following steps:

[0101] (1) Same as Example 3.

[0102] (2) Same as Example 3.

[0103] (3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating process; specifically: in a glove box, tetrahydrofuran and 1,2-dichloroethane with a volume ratio of 1:1 are used as solvents, VBTPA is used as hole transport material with a concentration of 5mg / mL, and spin coating is performed on an ITO / PEDOT:PSS substrate at a speed of 2000rpm for 60s. After annealing at 100℃ for 10 minutes, the hole transport layer is crosslinked at 175℃ for 20 minutes, and the film thickness is 30nm.

[0104] (4) The light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by spin coating process. Specifically, in a glove box, chloroform is used as solvent, and 4,4'-bis(9-carbazole)biphenyl (CBP) is used as the host material and doped with 15wt% green light-emitting material Ir(L)2(acac-Cz) as the light-emitting layer. The concentration of CBP is 10mg / mL. The coating is spin-coated on an ITO / PEDOT:PSS / HTL substrate at 4000rpm for 60s, annealed at 55℃ for 30 minutes, and the thickness is 70nm.

[0105] (5) Same as Example 3.

[0106] Example 6

[0107] A PhOLED device based on VBTPA as a thermally crosslinked HTL is provided, constructing an ITO / PEDOT:PSS (35nm) / VBTPA (20nm) / CBP:Ir(ppy)3 (30nm, 10wt%) / TPBI (50nm) / Liq (2nm) / Al device structure, wherein the light-emitting layer CBP:Ir(ppy)3 is prepared by vacuum evaporation, including the following steps:

[0108] (1) Same as Example 3.

[0109] (2) Same as Example 3.

[0110] (3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating process; specifically: in a glove box, tetrahydrofuran and 1,2-dichloroethane with a volume ratio of 1:1 are used as solvents, VBTPA is used as hole transport material with a concentration of 3mg / mL, and spin coating is performed on an ITO / PEDOT:PSS substrate at a speed of 2000rpm for 60s. After annealing at 100℃ for 10 minutes, the hole transport layer is crosslinked at 175℃ for 20 minutes, and the film thickness is 20nm.

[0111] (4) The light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by vacuum evaporation process. Specifically, CBP is used as the main material and doped with 10wt% green light-emitting material Ir(ppy)3. It is vacuum evaporated onto the substrate of ITO / PEDOT:PSS / HTL as the light-emitting layer with a thickness of 30nm.

[0112] (5) Same as Example 3.

[0113] Example 7

[0114] A PhOLED device based on VBPhCz and VBTPA as thermally crosslinked HTLs is provided, constructing an ITO / PEDOT:PSS (35nm) / VBPhCz&VBTPA (30nm) / CBP:Ir(L)2(acac-Cz) (70nm, 15wt%) / TPBI (50nm) / Liq (2nm) / Al device structure, wherein the light-emitting layer CBP:Ir(L)2(acac-Cz) is prepared by solution spin-coating, including the following steps:

[0115] (1) Same as Example 3.

[0116] (2) Same as Example 3.

[0117] (3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating process; specifically: in a glove box, tetrahydrofuran and 1,2-dichloroethane with a volume ratio of 1:1 are used as solvents, and VBPhCz and VBTPA are used as hole transport materials with a mass ratio of 1:1 and a total concentration of 5mg / mL. The mixture is spin-coated on an ITO / PEDOT:PSS substrate at a speed of 2000rpm for 60s, annealed at 100℃ for 10 minutes, and then crosslinked at 175℃ for 20 minutes. The film thickness is 30nm.

[0118] (4) The light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by spin coating process. Specifically, in a glove box, chloroform is used as solvent, and 4,4'-bis(9-carbazole)biphenyl (CBP) is used as the host material and doped with 15wt% green light-emitting material Ir(L)2(acac-Cz) as the light-emitting layer. The concentration of CBP is 10mg / mL. The coating is spin-coated on an ITO / PEDOT:PSS / HTL substrate at 4000rpm for 60s, annealed at 55℃ for 30 minutes, and the thickness is 70nm.

[0119] (5) Same as Example 3.

[0120] Example 8

[0121] A PhOLED device based on VBPhCz and VBTPA as thermally crosslinked HTLs is provided, constructing an ITO / PEDOT:PSS (35nm) / VBPhCz&VBTPA (20nm) / CBP:Ir(ppy)3 (30nm, 10wt%) / TPBI (50nm) / Liq (2nm) / Al device structure, wherein the light-emitting layer CBP:Ir(ppy)3 is prepared by vacuum evaporation, including the following steps:

[0122] (1) Same as Example 3.

[0123] (2) Same as Example 3.

[0124] (3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating process; specifically: in a glove box, tetrahydrofuran and 1,2-dichloroethane with a volume ratio of 1:1 are used as solvents, and VBPhCz and VBTPA are used as hole transport materials with a mass ratio of 1:1; the total concentration is 3mg / mL. The material is spin coated on an ITO / PEDOT:PSS substrate at a speed of 2000rpm for 60s, annealed at 100℃ for 10 minutes, and then crosslinked at 175℃ for 20 minutes. The film thickness is 20nm.

[0125] (4) The light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by vacuum evaporation process. Specifically, CBP is used as the main material and doped with 10wt% green light-emitting material Ir(ppy)3. It is vacuum evaporated onto the substrate of ITO / PEDOT:PSS / HTL as the light-emitting layer with a thickness of 30nm.

[0126] (5) Same as Example 3.

[0127] The device structure was constructed using ITO / PEDOT:PSS (35nm) / HTL (20nm) / CBP:Ir(ppy)3 (30nm, 10wt%) / TPBI (50nm) / Liq (2nm) / Al. PEDOT:PSS and HTL (3mg / mL) were deposited via solution spin-coating, followed by vacuum evaporation of the CBP:Ir(ppy)3 light-emitting layer. Figure 8 Table 2), the startup voltage (V) of the device with VBPhCz as the hole transport layer alone (Example 4). on The voltage is 5.5V, and the maximum brightness is 30530 cd / m². 2 The maximum current efficiency (Max.CE) is 18.8 cd / A; while the device using VBTPA as the hole transport layer alone (Example 6) has a startup voltage of 6.0V and a maximum luminance of 26790 cd / m². 2 The device (Example 8) with a maximum current efficiency of 12.1 cd / A, using a 1:1 volume ratio mixture of VBPhCz (3 mg / mL) and VBTPA (3 mg / mL) as the hole transport layer, had a startup voltage of 5.7 V and a maximum luminance of 22450 cd / m². 2 The maximum current efficiency is 12.6 cd / A. With the increase of the mixing ratio of VBPhCz, which has stronger rigidity and higher triplet energy levels, in the thermally crosslinked HTL, the performance of green PhOLED devices based on vacuum evaporation of the emissive layer is continuously improved. Therefore, adjusting the ratio of VBPhCz and VBTPA can effectively control the HTL and improve the device performance.

[0128] Table 2 Device performance of green PhOLED devices with vacuum-deposited emissive layers

[0129]

[0130] The device structure was constructed by spin-coating PEDOT:PSS (35nm) / HTL (30nm) / CBP:Ir(L)2(acac-Cz) (70nm, 15wt%) / TPBI (50nm) / Liq (2nm) / Al. PEDOT:PSS, HTL (5mg / mL), and CBP:Ir(L)2(acac-Cz) were sequentially deposited using a solution-based method. Figure 9 (Table 3). The device with cross-linked VBTPA used alone as the hole transport layer (Example 5) had a startup voltage of 6.1V and a maximum luminance of 8271 cd / m². 2 The maximum current efficiency is 12.4 cd / A; the cross-linked VBPhCz, used alone as a hole transport layer (Example 3), has a start-up voltage of 7.2 V and a maximum luminance of 8066 cd / m². 2 The maximum current efficiency was 10.6 cd / A; the device (Example 7) using a 1:1 volume ratio mixture of VBPhCz (5 mg / mL) and VBTPA (5 mg / mL) as the hole transport layer had a startup voltage of 7.8 V and a maximum luminance of 5880 cd / m². 2 A green PhOLED device with a maximum current efficiency of 5.8 cd / A was achieved, realizing a solution-based fabrication method for a multifunctional layer including the emissive layer. When cross-linked VBTPA was used as the hole transport layer, device performance comparable to that of a green PhOLED device with a vacuum-deposited emissive layer was obtained.

[0131] Table 3. Device performance of green PhOLED devices spin-coated using the solution method for the emitting layer.

[0132]

[0133] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a low-temperature, short-time thermal cross-linking material as a hole transport material, characterized in that, The thermal crosslinking material is VBPhCz and / or VBTPA; wherein: The structural formulas of VBPhCz and VBTPA are shown below: 。 2. The application according to claim 1, characterized in that, The method for preparing the thermally crosslinked material includes the following steps: Under inert gas protection, 3-bromo-9-(4-bromophenyl)carbazole or bis(4-bromophenyl)aniline, 4-vinylphenylboronic acid and catalyst are stirred and heated to 100-110℃ in a mixed solution of tetrahydrofuran and potassium carbonate aqueous solution to carry out a coupling reaction and obtain a low-temperature short-time thermal crosslinking material.

3. A hole transport layer, characterized in that, The hole transport layer is prepared from a low-temperature, short-time thermal cross-linking material; The thermal crosslinking material is VBPhCz and / or VBTPA; wherein: The structural formulas of VBPhCz and VBTPA are shown below: 。 4. The hole transport layer according to claim 3, characterized in that, The hole transport layer was prepared by a solution method.

5. The application of the hole transport layer according to claim 3 or 4 in PhOLED.

6. A PhOLED device, comprising a substrate, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and electrodes, characterized in that, The hole transport layer is the hole transport layer as described in claim 3 or 4; the light-emitting layer is prepared by solution method or vacuum evaporation process.

7. A method for fabricating the PhOLED device according to claim 6, characterized in that, Includes the following steps: 1) Clean and pre-treat the ITO glass; 2) A hole injection layer is prepared on the ITO surface obtained in step 1) by spin coating; 3) A hole transport layer is prepared on the surface of the hole injection layer obtained in step 2) by spin coating; 4) A light-emitting layer is prepared on the surface of the hole transport layer obtained in step 3) by spin coating or vacuum evaporation. 5) ETL, EIL and electrodes are sequentially prepared on the surface of the light-emitting layer obtained in step 4) by vacuum evaporation process to obtain the PhOLED device.

8. The preparation method according to claim 7, characterized in that, In step 3), VBPhCz and / or VBTPA are used as hole transport materials; the concentration of hole transport materials is 3-5 mg / mL; when VBPhCz and VBTPA are used simultaneously, the mass ratio is 4:5 to 5:

4.

9. The preparation method according to claim 7, characterized in that, In step 3), the spin coating process conditions are as follows: spin coating at 2000-2500 rpm for 55-60 s, annealing at 100-110℃ for 10-15 minutes, and then crosslinking at 130-175℃ for 18-22 minutes. In step 4), the spin coating process conditions are: spin coating at 4000-4500 rpm for 55-60 s, followed by annealing at 55-60℃ for 30-35 minutes.

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