Preparation method of Nb2CTx-MXene nanosheet hole injection layer material

Abstract

The invention belongs to the technical field of semiconductor photoelectronics, and particularly relates to a preparation method of an Nb2CTx-Mxene nanosheet hole injection layer material, which comprises the following steps of: dispersing an Nb2CTx-Mxene nanosheet in a dispersion medium to form a dispersion liquid, coating the surface of a transparent conductive substrate with the dispersion liquid, removing the dispersion medium through annealing treatment to form a thin film, and preparing the Nb2CTx-Mxene nanosheet hole injection layer material. And carrying out ultraviolet ozone treatment on the film to obtain the hole injection layer material. By regulating and controlling the ultraviolet ozone treatment time, the surface appearance of the film can be optimized, and the work function of the film can be adjusted, so that the film is matched with the energy level of an adjacent functional layer, and efficient hole injection is realized. The hole injection layer prepared by the method has high light transmittance (greater than 98%), low roughness and proper work function, can significantly improve the efficiency and stability of OLED devices, and is suitable for various photoelectric devices such as solar cells, photoelectric detectors and the like.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic technology, and relates to a hole injection layer material, particularly a method for preparing a hole injection layer material that can be applied to nano-optoelectronic devices such as organic light-emitting diodes and solar cells. Background Technology

[0002] Organic light-emitting diodes (OLEDs) have been widely used in the display and lighting fields due to their unique performance advantages. Compared with traditional display technologies, OLEDs can achieve true "black" displays because their non-excited pixels are completely non-emitting, eliminating the need for a backlight module and significantly reducing energy consumption. Furthermore, OLEDs also possess outstanding characteristics such as self-emission, flexibility, and transparency. Among various manufacturing processes, solution-processed OLEDs have attracted considerable attention due to their suitability for large-area, flexible production and lower manufacturing costs.

[0003] However, these devices still face many challenges in practical applications. Among them, finding high-performance hole injection materials on indium tin oxide (ITO) anodes is one of the keys to improving the efficiency and stability of OLED devices.

[0004] Currently, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is widely used as a hole injection layer material in OLED devices. However, the acidity of PEDOT:PSS itself can corrode ITO electrodes and damage organic functional layers, leading to performance degradation and shortened lifetime of OLED devices. To alleviate this problem, a shielding layer is often introduced between PEDOT:PSS and ITO or organic layers to isolate acidic substances, but this increases the complexity of the device structure and the difficulty of manufacturing processes. Therefore, developing an alternative material that possesses the excellent hole injection characteristics of PEDOT:PSS without acidity has become an important way to fundamentally improve the performance of OLEDs.

[0005] In recent years, researchers have actively explored various alternative materials for PEDOT:PSS, mainly including metal oxides (such as molybdenum oxide, nickel oxide, vanadium oxide, etc.), metal complexes (such as cuprous thiocyanate complexes, etc.), and two-dimensional materials (such as graphene oxide, molybdenum disulfide, tungsten disulfide, and transition metal carbon / nitrides (MXene), etc. Among them, MXene, since its first report in 2011, has shown great application potential in the optoelectronic field due to its high electrical conductivity, tunable surface functional groups, and excellent optical properties.

[0006] MXene has a two-dimensional layered structure similar to graphene, with the general formula M n+1 Xn T x In this MXene formula, M represents the pre-transition metal, X is carbon or nitrogen, and T is the surface functional group. Currently, approximately 30 MXenes have been successfully synthesized, with Ti3C2T being the most widely used. x -MXene and Nb2CT x -MXene, and Nb2CT x -MXene compared to Ti3C2T x -MXene has a larger specific surface area and is a two-dimensional material with great potential in the field of OLEDs.

[0007] For multi-functional layer OLED devices, Nb2CT x The high specific surface area of ​​MXene helps to increase its interfacial contact with adjacent functional layers, improving charge injection efficiency; at the same time, its work function can be tuned through surface functional group modification, thereby matching the requirements of different transport energy levels, making it a highly promising hole injection material. Therefore, by tuning Nb2CT... x Exploring the surface chemical properties of MXene and further optimizing its performance as a hole injection layer has become a current research hotspot.

[0008] Against this backdrop, the goal is to develop novel and simple fabrication processes to achieve Nb2CT with high transmittance, low surface roughness, suitable work function, and excellent stability. x MXene hole injection layer materials are of great significance for promoting the development of next-generation high-performance, long-life OLED devices. Summary of the Invention

[0009] The purpose of this invention is to provide an Nb2CT x - A method for preparing MXene nanosheet hole injection layer material, which further improves the device performance of OLEDs through the formation of hole injection layer thin film.

[0010] The Nb2CT of the present invention x The preparation method of the -MXene nanosheet hole injection layer material is to use Nb2CT x MXene nanosheets are dispersed in a dispersion medium to form a dispersion liquid, which is then uniformly coated onto the surface of a transparent conductive substrate material. The dispersion medium is removed by annealing under vacuum or inert gas protection to form Nb2CT. x -MXene film, and then the surface of the film is treated with ultraviolet ozone to obtain hole injection layer film material loaded on the surface of transparent conductive substrate material.

[0011] The Nb2CT of the present invention xThe preparation method of the MXene nanosheet hole injection layer material does not have any special requirements for the transparent conductive substrate material used to support the hole injection layer film material. It can be any conventional material that can be used as a transparent conductive substrate, including but not limited to any transparent conductive anode such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO).

[0012] Preferably, the transparent conductive substrate material of the present invention is indium tin oxide (ITO).

[0013] In this invention, the Nb2CT x -MXene nanosheets can be Nb2CT prepared according to any of the methods reported in the literature. x -MXene.

[0014] For example, a wet chemical etching and ultrasonic stripping method can be used to dissolve lithium fluoride (LiF) in hydrochloric acid (HCl) solution, add Nb2AlC powder for hydrothermal reaction, wash the reaction product until neutral, sonicate, and centrifuge to collect the supernatant to obtain Nb2CT. x -MXene nanosheets.

[0015] Specifically, it is preferable to centrifuge the ultrasonically treated product at 3000-8000 r / min and collect the supernatant.

[0016] The dispersion medium described in this invention can be any medium with good Nb2CT properties. x The polar solvents that enable the dispersion of MXene nanosheets include, but are not limited to, any one of water, ethanol, acetone, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, or propylene carbonate, or mixtures of several in any proportion. Preferably, the dispersion medium described in this invention is selected from water.

[0017] Furthermore, the present invention preferably uses Nb2CT x MXene nanosheets are dispersed in a dispersion medium to form a dispersion with a concentration of 0.2–0.4 mg / ml.

[0018] Furthermore, the annealing temperature described in this invention should be higher than the boiling point of the dispersion medium, and the annealing time is preferably 5 to 60 minutes.

[0019] Furthermore, the preferred time for ultraviolet ozone treatment of the film surface after annealing is 8 to 15 minutes.

[0020] Nb2CT loaded on the surface of a transparent conductive substrate material was prepared using the method described above in this invention. x-MXene nanosheet hole injection layer material has excellent light transmittance of more than 98%, and can be used to prepare OLED devices.

[0021] Specifically, it is in the Nb2CT prepared in this invention x OLED devices can be fabricated by directly vacuum-depositing other organic functional layer materials and cathode materials on the surface of the MXene nanosheet hole injection layer material.

[0022] Furthermore, the Nb2CT described in this invention x -MXene nanosheet hole injection layer materials can also be used in the fabrication of optoelectronic devices such as solar cells and photodetectors.

[0023] This invention combines wet chemical etching with ultrasonic ablation to prepare Nb2CT with a main size distribution of 400–800 nm. x -MXene nanosheets were spin-coated onto a transparent conductive substrate, annealed to form a thin film, and then subjected to ultraviolet ozone treatment to finally obtain Nb2CT. x -MXene nanosheet hole injection layer thin film material. Appropriate UV ozone treatment time not only reduces film roughness but also enhances Nb2CT... x The number of functional groups on the MXene surface changes, and the work function (WF) is adjusted from 4.84 eV to 5.05 eV, thereby achieving a work function that matches that of its adjacent functional layers. Incorporating it between the ITO anode and the hole transport layer (HTL) enables ideal cascaded hole injection, further improving the balance of carrier transport in OLEDs. Therefore, the Nb2CT prepared in this invention... x -MXene nanosheet films can replace PEDOT:PSS as a highly efficient hole injection layer (HIL) for OLEDs.

[0024] The present invention experimentally demonstrates that, with Nb2CT x The green phosphorescent OLED based on Ir(ppy)3, fabricated using MXene nanosheets for HIL, exhibits a low turn-on voltage of 3.0V and achieves maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 101.46 cd / A, 95.15 lm / W, and 28.62%, respectively, significantly outperforming PEDOT:PSS's 67.72 cd / A, 41.67 lm / W, and 19.45%. Furthermore, it incorporates Nb2CT... x Similar results were also confirmed in blue and red phosphorescent devices based on MXene nanosheet thin films of HIL. Furthermore, Nb2CT-based... xThe device based on MXene nanosheet film also exhibited extremely high stability, significantly outperforming the reference device based on PEDOT:PSS, indicating that Nb2CT... x MXene nanosheets are a promising hole injection material (HIM) with enormous application potential. Attached Figure Description

[0025] Figure 1 This invention is Nb2CT x -Schematic diagram of the synthesis of MXene nanosheets.

[0026] Figure 2 This invention prepares Nb2CT x X-ray diffraction pattern of MXene nanosheets.

[0027] Figure 3 This invention prepares Nb2CT x Transmission electron microscopy image of MXene nanosheets.

[0028] Figure 4 This invention prepares Nb2CT x X-ray photoelectron spectrum of MXene nanosheets.

[0029] Figure 5 It is Nb2CT in Example 2 x Comparison of X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy of MXene nanosheet thin films and hole injection layer thin film materials obtained by ultraviolet ozone treatment.

[0030] Figure 6 Nb2CT was obtained under different conditions in Example 3. x Atomic force microscopy image of the roughness of MXene nanosheet films.

[0031] Figure 7 This is a graph showing the changes in transmittance of different hole injection layer thin film materials in Comparative Example 1.

[0032] Figure 8 The normalized electroluminescence spectra (a), current efficiency-voltage-brightness curves (b), current efficiency-brightness curves-external quantum efficiency curves (c), power efficiency-brightness curves (d), and brightness-time decay curves of the green phosphorescent device are shown in Example 1.

[0033] Figure 9 Examples 2 show the current density-voltage-brightness curves (a, d), current efficiency-brightness-external quantum efficiency curves (b, e), and power efficiency-brightness curves (c, f) for each device, as well as the normalized electroluminescence spectrum (g) and external quantum efficiency-brightness curve (h) of the OLED at 5V. Implementation

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and specific examples. It should be noted that the embodiments are merely illustrative and are intended to provide a thorough understanding of the technical solutions of the present invention and to provide guidance for those skilled in the art to implement and apply the present invention. It should be understood that these descriptions do not constitute any limitation on the scope of protection of the present invention.

[0035] Unless otherwise expressly stated, the production processes, experiments, tests or analysis methods involved in the embodiments of the present invention are all considered to be conventional methods known to those skilled in the art, and only need to be implemented in accordance with conventional conditions or relevant product instructions. The steps and names involved are also generally clear and unambiguous in the art.

[0036] The instruments, equipment, raw materials, reagents, or samples used in the embodiments are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels or prepared by known methods, and their source does not have a substantial impact on the implementation results of the present invention.

[0037] Unless otherwise expressly defined, the scientific and technical terms used in this invention have the meanings commonly understood by one of ordinary skill in the art. In case of any conflict, the definitions in this specification shall prevail.

[0038] The terms “comprising,” “including,” “having,” etc., used in this invention should be understood as open-ended, meaning “including but not limited to.” The term “and / or” includes any and all combinations of one or more of the associated listed items. Quantitative terms such as “a,” “one,” etc., do not exclude multiples; “multiple” or “a variety” refers to quantities greater than or equal to two.

[0039] The terms "preferred", "better", and "exemplary" used in this invention are only used to describe specific solutions or effects and are not intended to limit the necessary scope of the solution or the scope of protection.

[0040] This invention relates to the description of numerical parameters (such as quantity, concentration, temperature, time, etc.), and it should be understood that reasonable deviations naturally exist due to measuring instruments, operational errors, statistical fluctuations, etc. The range of such deviations should be within limits acceptable to those skilled in the art based on common sense.

[0041] Nb2CT involved in the embodiments of the present invention x The preparation method of the MXene nanosheet hole injection layer material is as follows:

[0042] I. Nb2CT x Synthesis of MXene Nanosheets

[0043] 1) First, dissolve LiF in HCl of a certain concentration and stir until it is fully dissolved.

[0044] 2) Slowly add Nb2AlC to the above solution and react at 110°C for no less than 3.5 days.

[0045] 3) After the reaction is complete, wash repeatedly with deionized water by centrifugation until the pH value is close to 6.

[0046] 4) Remove the supernatant, retain the clay-like precipitate, add deionized water as the dispersion medium, and sonicate under a nitrogen atmosphere for 2 hours to obtain the initial Nb2CT. x -MXene nanosheet dispersion.

[0047] 5) Finally, the dispersion was centrifuged at 4800 r / min for 15 min, and the supernatant was collected to obtain the final Nb2CT for film formation. x -MXene nanosheet dispersion.

[0048] II. Nb2CT x Preparation of MXene nanosheet hole injection layer material

[0049] 1) The ITO substrate was ultrasonically cleaned with deionized water, acetone and isopropanol for 15 minutes in sequence, and then dried in a constant temperature drying oven at 60℃ to obtain a clean and dust-free ITO substrate.

[0050] 2) Remove the dried ITO substrate from the constant temperature drying oven and place it in a UV box. Irradiate it with UV lamps for a certain period of time to further remove residual organic matter on the surface of the ITO substrate and improve the wettability of the ITO substrate.

[0051] 3) Depositing Nb2CT on ITO substrates using solution methods (solution spin coating, solution spraying, etc.) x -MXene nanosheet dispersion to obtain a thin film layer, Nb2CT formed under inert gas protection or vacuum. x The MXene film was annealed at a temperature above 100°C for 5–60 min, and then subjected to UV ozone treatment for 8–15 min to obtain Nb2CT loaded on an ITO substrate. x -MXene nanosheet hole injection layer material.

[0052] The OLED devices involved in the embodiments of the present invention are prepared using a high-vacuum thermal evaporation process.

[0053] I. Nb2CT x -MXene nanosheet hole injection layer material cavity

[0054] The prepared Nb2CT loaded on the ITO substrate xThe MXene nanosheet hole injection layer material is rapidly placed onto a mask, and the mask is then introduced into a vacuum evaporation chamber.

[0055] II. Vacuuming the equipment

[0056] Turn on the power supply, mechanical pump, and molecular pump of the high vacuum coating machine in sequence to evacuate the vacuum chamber.

[0057] III. Thermal Evaporation Preparation of Organic Light-Emitting Diodes

[0058] When the vacuum level inside the high vacuum coating machine cavity is lower than 5×10 -4 At Pa, the thermal evaporation sources of the electron injection layer material, hole and electron transport layer materials, and other functional and luminescent materials loaded in the cavity are heated separately. Based on the designed device structure, Nb2CT... x - Various functional layers are sequentially thermally deposited on the MXene nanosheet hole injection layer material.

[0059] The mask is rotated horizontally to align the position of the aluminum cathode deposition mask with the hole injection layer film. A thermal evaporation source equipped with aluminum wire is heated to deposit the aluminum cathode, and finally a complete organic light-emitting diode is prepared.

[0060] During device fabrication, the evaporation rate and film thickness were monitored using a quartz crystal frequency meter connected to the outside of the vacuum chamber. The evaporation rates for various organic functional materials, LiF, and aluminum were approximately 1 Å / s, 0.1 Å / s, and 3 Å / s, respectively. The effective light-emitting area of ​​the device was ultimately determined by the overlap of the patterned transparent anode and the aluminum cathode, resulting in an effective light-emitting area of ​​3 mm × 3 mm.

[0061] The performance of the OLEDs prepared in the embodiments was tested according to the following method.

[0062] The prepared OLED was removed from the vacuum chamber, and the current density, current efficiency, and brightness of the device were obtained using a computer-integrated controlled BM-7A photometer and a Keithley 2400 digital source meter. The electroluminescence spectrum, color coordinates, and color rendering index of the device under different voltages were obtained using a computer-integrated controlled Spectra Scan PR655 spectroradiometer. Example

[0063] Example 1

[0064] Place 2g of LiF and 20ml of 12M HCl solution in a 100ml Teflon-lined reactor and stir for 30min to fully dissolve them. Then slowly add 2g of Nb2AlC powder, seal the reactor, and perform a hydrothermal reaction in an oven at 110℃ for 3.5 days.

[0065] After the reaction product was cooled to room temperature, it was washed repeatedly by centrifugation with deionized water and ethanol at 3000 r / min until the pH value was greater than 6. Then, it was placed in a vacuum drying oven and dried at 60℃ for 12 h to obtain a powder precipitate. The precipitate was then ground into a fine powder in an agate mortar and placed in a small bottle for later use.

[0066] Weigh 500 mg of the above powder and place it in a gas washing bottle. Add 120 ml of deionized water and purge the bottle with nitrogen gas for 30 min. Then seal both ends of the gas washing bottle to prevent air from entering. Place the sealed gas washing bottle in a 300 W ultrasonic bath and sonicate for 2 h. Remove the liquid from the gas washing bottle after sonication and centrifuge at 4800 r / min. Collect the supernatant, which is Nb2CT. x Aqueous dispersion of nanosheets.

[0067] Figure 1 The above-mentioned method of selectively etching Al from Nb₂AlC using a mixture of LiF and HCl to synthesize multilayer Nb₂CT via hydrothermal method is presented. x Then, multilayer Nb2CT x A schematic diagram of the synthesis process of obtaining few-layer nanosheets by ultrasonic exfoliation, where the upper part shows the macroscopic shape changes of the nanosheets and the lower part shows the changes at the molecular structure level of the nanosheets.

[0068] Figure 2 Nb2AlC and Nb2CT are provided. x The XRD pattern shows that during etching and stripping, the (002) diffraction peak of Nb2AlC shifted to 7.4°, while other diffraction peaks of Nb2AlC decreased drastically, indicating successful removal of the Al layer and the removal of Nb2CT. x - The interlayer spacing of MXene nanosheets is increased.

[0069] from Figure 3 Nb2CT x The transmission electron microscopy (TEM) images of MXene nanosheets show that MXene is in the form of smooth, uniform sheets with a lateral size of 200–500 nm.

[0070] Figure 4 In the XPS image, Nb2CT can be observed. x The surface of MXene nanosheets is rich in functional groups. The presence of F and O elements indicates that its surface functional groups may include -O, -OH and -F, which provides possibilities for subsequent surface modification.

[0071] Example 2

[0072] A patterned ITO substrate with an area of ​​1.97cm × 1.97cm was taken and ultrasonically cleaned with deionized water, acetone and isopropanol for 15 minutes in sequence. It was then dried in a constant temperature drying oven at 60℃ to obtain a clean and dust-free ITO substrate.

[0073] The dried ITO substrate is then placed in a UV chamber and irradiated with a UV lamp for 15 minutes to further remove residual organic matter on the substrate surface and improve the wettability of the ITO substrate.

[0074] Take the Nb2CT prepared in Example 1 x Aqueous dispersion of nanosheets, with the concentration of nanosheets adjusted to 0.3 mg / ml.

[0075] Spin-coat 70 μl of the 0.3 mg / ml aqueous dispersion onto the pre-treated ITO substrate at 3000 rpm. Place the substrate in a glove box and anneal at 120°C for 15 min until the water has completely evaporated, forming Nb2CT. x -MXene nanosheet thin film.

[0076] The above load has Nb2CT x -MXene nanosheets were placed on an ITO substrate in an ozone atmosphere and irradiated with a UV lamp for 10 minutes to prepare a hole injection layer film material loaded on the surface of a transparent conductive substrate.

[0077] The Nb2CT prepared above without ultraviolet ozone treatment was tested separately. x X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) of MXene nanosheet thin films and hole injection layer thin film materials obtained after ultraviolet ozone treatment are shown in the figure. Figure 6 As shown.

[0078] Figure 6 XPS images of a, b, and c show Nb2CT. x -MXene nanosheets are mainly composed of four elements: Nb, C, O, and F. Furthermore, whether or not ultraviolet ozone treatment is performed does not change the Nb2CT content. x -Elemental types present in MXene nanosheets. In the Nb 3d region, after 10 min of UV ozone treatment, the Nb-C content decreased from 28.44% to 6.55%, while the Nb-O content increased from 71.56% to 93.45%. These results are consistent with those observed in the C 1s and O 1s spectra. The C 1s spectrum was deconvoluted to four peaks, where the C-Nb content decreased from 12.54% to 0.36%, resulting in a 10.07% increase in C-C bonds and an 8.13% increase in C=O bonds, demonstrating carbon production and oxygen oxidation. The O 1s spectrum further confirmed these findings, with the Nb₂O₅ content increasing from 64.81% to 66.47%.

[0079] Figure 6 The UPS of the middle d further evaluated the effect of ultraviolet ozone treatment on Nb2CT.x Quantitative influence of MXene nanosheet work function. Among them, the original Nb2CT... x The secondary electron cutoff edge of the MXene nanosheet is 16.38 eV, and the calculated work function is 4.84 eV. After UV ozone treatment, the secondary electron cutoff edge of the hole injection layer film material is reduced to 16.17 eV, and the work function increases to 5.05 eV. This significantly improved work function can promote energy level alignment with typical hole transport layers, which have the highest occupied molecular orbital levels of approximately 5.2–5.5 eV, thus potentially minimizing recombination energy losses associated with hole injection at the hole injection layer / hole transport layer interface in OLEDs.

[0080] Example 3

[0081] The Nb2CT prepared in Example 2 x -MXene nanosheet films were subjected to UV ozone treatment for 0, 5, 10, and 20 min respectively to obtain hole injection layer film materials. The roughness of the film materials was then measured. Figure 6 a to d in the example.

[0082] Nb2CT at concentrations of 0.1, 0.5, and 0.7 mg / ml were taken respectively. x Aqueous dispersion of nanosheets, prepared according to the method in Example 2, yielded Nb2CT. x -MXene nanosheet thin films were subjected to 10 min of UV ozone treatment to obtain hole injection layer thin film materials. The roughness of the thin film materials was tested, and the corresponding... Figure 6 f to h in the text.

[0083] in addition, Figure 6 The image provided shows an atomic force microscope (AFM) image of the roughness of a bare ITO substrate.

[0084] Figure 6 The roughness results show that the root mean square (RMS) roughness of the bare ITO substrate is 2.372 nm. Under the same UV ozone treatment condition of 10 min, the RMS roughness of the 0.3 mg / ml film (c) is 2.646 nm, slightly lower than the 2.839 nm of the 0.1 mg / ml film (f), and there is no significant change compared to the roughness of the untreated bare ITO substrate. This demonstrates that the film coating has excellent uniformity, which is attributed to the relatively high Nb2CT. x The higher concentration of MXene nanosheets resulted in a denser and smoother surface. However, when the concentration increased to 0.5 mg / ml (g) and 0.7 mg / ml (h), the RMS of both films significantly increased to 4.116 nm and 4.894 nm, respectively. This is easily understood; higher concentrations lead to the aggregation of nanosheets during spin-coating, thereby reducing Nb2CT.x The uniformity of the MXene nanosheet film is a concern. Such a rough film is clearly detrimental to the fabrication of thin-film light-emitting devices, as these particle clusters would act as charge trapping sources and non-radiative recombination centers, significantly reducing device performance. Based on the above analysis, the fabrication of Nb2CT... x The suitable dispersion concentration for MXene nanosheet films is 0.2–0.4 mg / ml.

[0085] Under the condition that the dispersion concentration is also 0.3 mg / ml, Nb2CT x The surface roughness of the MXene nanosheet film is highly dependent on the duration of UV ozone treatment. Without UV ozone treatment, the pristine nanosheet film (a) exhibits a significantly undulating surface with a maximum mean of 3.966 nm. After 5 min (b) and 10 min (c) of UV ozone treatment, the RMS of the corresponding nanosheet films decreased to 3.021 nm and 2.646 nm, respectively. However, when the UV ozone treatment time was further increased to 20 min (d), the RMS increased in the opposite direction to 3.594 nm. The decrease in surface roughness may be related to the oxidation that occurs on the surface of the nanosheet film during UV ozone treatment. The pristine nanosheet film contains a large number of dangling bonds, and inevitably also contains some interleaved and stacked Nb2CT bonds. x -MXene nanosheets, this is likely the fundamental reason for the high surface roughness. During UV ozone treatment, protruding surfaces and dangling bonds are rapidly oxidized first, forming a thin oxide layer that passivates the nanosheet film surface, helping to reduce roughness. However, prolonged exposure to UV ozone may lead to excessive oxidation of the film surface and damage to the crystal layer, which is why Nb2CT was subjected to 20 minutes of UV ozone treatment. x The reason for the reverse increase in the RMS value of the MXene nanosheet film is that the preferred UV ozone treatment time is 8–15 min.

[0086] Compare with Example 1

[0087] Nb2CT x The nanosheet aqueous dispersion was replaced with PEDOT:PSS, and PEDOT:PSS thin film material was prepared by spin-coating onto an ITO substrate according to the method in Example 2, without ultraviolet ozone treatment.

[0088] The transmittance of the PEDOT:PSS thin film material (TP) was tested and compared with that of Nb2CT at concentrations of 0.1, 0.3, 0.5, and 0.7 mg / ml, respectively. x Comparison of the light transmittance of hole injection layer thin film materials prepared by nanosheet aqueous dispersion.

[0089] Figure 7 Characterization results show that all Nb2CT xThe MXene nanosheet film exhibited excellent transmittance, exceeding 98.3%, across the entire visible light wavelength range of 380–780 nm. Changes in dispersion concentration had virtually no effect on the film's transmittance, which is attributed to Nb₂CT. x MXene nanosheets exhibit excellent transparency. The overall transmittance of all nanosheet films is significantly higher than that of PEDOT:PSS films, which allows light emitted from the light-emitting layer to be effectively output to the outside of the device through the hole injection layer, thereby improving device performance.

[0090] Application Example 1

[0091] The Nb2CT prepared in Example 2 x -MXene nanosheet films were subjected to ultraviolet ozone treatment for 0, 5, 10 and 20 min to obtain different hole injection layer thin film materials (HILs) for the fabrication of green phosphorescent OLED devices. The same OLED device was prepared using the PEDOT:PSS-based hole injection layer prepared in Comparative Example 1 as a control.

[0092] The specific device structure is as follows: Glass substrate / ITO / HILs / TAPC (40nm) / TCTA (10nm) / Bepp2: 6wt% Ir(ppy)3 (20nm) / TmPyPB (45nm) / LiF (1nm) / Al (100nm).

[0093] In the above devices, ITO serves as the anode; TAPC serves as the hole transport layer; TCTA serves as the electron and exciton blocking layer; Bepp2: 6wt% Ir(ppy)3 is used as the phosphorescent organic light-emitting layer; TmPyPB and LiF are used as the electron transport layer and electron injection layer, respectively, and aluminum (Al) is used as the cathode.

[0094] TAPC: Di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane;

[0095] TCTA: 4,4',4-Tris(carbazol-9-yl)triphenylamine;

[0096] Bepp2: Bis(10-hydroxybenzo[h]quinolinato)beryllium;

[0097] Ir(ppy)3: tris[2-(p-tolyl)pyridine-C2,N)]iridium(III);

[0098] TmPyPB: 1,3,5-Tri[(3-pyridyl)-phen-3-yl]benzene.

[0099] Figure 8 The normalized electroluminescence spectrum (a), current efficiency-voltage-brightness curve (b), current efficiency-brightness curve-external quantum efficiency (c), and power efficiency-brightness curve (d) of the above-mentioned different devices, as well as the brightness and time decay curve of the green phosphorescent device (e), were tested respectively.

[0100] from Figure 8 As can be seen from (a), (b), (c), and (d), the device treated with ultraviolet ozone for 10 min achieved the highest efficiency, with maximum current efficiency, power efficiency, and external quantum efficiency reaching 101.46 cd / A, 95.15 lm / W, and 28.62%, respectively. In contrast, the efficiency of the control device based on PEDOT:PSS was only 67.72 cd / A, 41.67 lm / W, and 19.45%, respectively.

[0101] Figure 8 (e) Stability testing was performed by recording luminance decay under constant voltage. All devices were stored unencapsulated and in an N2 glove box at room temperature. The drive voltage was approximately 1000 cd / m². 2 The initial brightness was determined and used as the test voltage for subsequent measurements, and was performed every 10 hours.

[0102] Nb2CT x -MXene-based hole injection layer devices exhibit 1237 cd / m² at an initial voltage of 5.7 V. 2 The brightness of the device was significantly higher than that of the control device PEDOT:PSS, which showed 970 cd / m² at an initial voltage of 5.4V. 2 The brightness.

[0103] After five tests (50 hours), Nb2CT x The luminance of the MXene-based hole injection layer device remained at 621.7 cd / m². 2 The brightness of the control device decreased by only 49.7%, while the brightness of the control device dropped significantly to 85.84 cd / m². 2 The degradation was 91.2%. Even with a higher initial drive voltage and brightness, based on Nb2CT... x The brightness decrease of the MXene nanosheet device was still significantly smaller compared to the control device based on PEDOT:PSS.

[0104] Application Example 2

[0105] To further demonstrate the feasibility of the technical solution of this invention, red and blue phosphorescent devices were fabricated. The specific device structure is ITO / HILs / TAPC (40nm) / TCTA (10nm) / emitting layer (20nm) / TmPyPB (45nm) / LiF (1nm) / Al (100nm).

[0106] The emitting layer of the blue light device is mCP: 15wt% FIrpic; the emitting layer of the red light device is Bepp2: 4wt% Ir(5BPQ-35Me)2acac. The hole injection layer is the same as in Application Example 1.

[0107] mCP: 1,3-Bis(N-carbazolyl)benzene;

[0108] FIrpic: Bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III);

[0109] Ir(5BPQ-35Me)2acac:bis(2-(4,5-dimethylbenzena)quinoline-5-butyl)(acetylacetonate)iridium(III).

[0110] Figure 9 The normalized electroluminescence spectrum (a), current efficiency-voltage-luminance curve (b), current efficiency-luminance curve-external quantum efficiency (c), and power efficiency-luminance curve (d) of the above devices are presented.

[0111] In the image, Nb2CT x -MXene-based and PEDOT:PSS-based blue light emitters achieved maximum brightness of 14990 and 15000 cd / m², respectively. 2 They are almost at the same level, but Nb2CT x The maximum current efficiency, power efficiency, and external quantum efficiency of the MXene device are as high as 45.14 cd / A, 42.98 lm / W, and 22.53%, respectively, which are significantly higher than those of PEDOT:PSS-based devices.

[0112] With Nb2CT x The red light device with the MXene nanosheet hole injection layer exhibits both higher brightness and efficiency, with a maximum brightness and external quantum efficiency of 46530 cd / m². 2 And 27.67%, but PEDOT:PSS-based red light devices only have 25350 cd / m². 2 and 15.77%.

[0113] The high device efficiency further demonstrates the effectiveness of 0.3 mg / ml Nb2CT under 10 min of UV ozone treatment. x The practicality of MXene-based hole injection layers, along with the successful fabrication of green, blue, and red light devices based on this film, demonstrates the universality of the film and provides a new method for replacing PEDOT:PSS as a new hole injection layer.

[0114] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Nb2C x The preparation method of the MXene nanosheet hole injection layer material is to prepare Nb2C x The MXene nanosheet is dispersed in a dispersion medium to form a dispersion liquid, uniformly coated on the surface of the transparent conductive substrate material, and subjected to annealing treatment under vacuum or inert gas protection to remove the dispersion medium to form a Nb2C x The MXene thin film, and the surface of the thin film is subjected to ultraviolet ozone treatment to obtain a hole injection layer thin film material loaded on the surface of the transparent conductive substrate material.

2. The method of claim 1 wherein The annealing treatment temperature is higher than the boiling point of the dispersion medium, and the annealing time is 5-60 minutes.

3. The method of claim 1 wherein The ultraviolet ozone treatment time is 8-15 minutes.

4. The method of claim 1 wherein The dispersion medium is one or more of water, ethanol, acetone, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone or propylene carbonate in any proportion.

5. The method of claim 1 wherein The dispersion medium is water.

6. The method of claim 1 wherein Nb2CT x MXene nanoplatelets are dispersed in a dispersion medium to form a dispersion liquid with a concentration of 0.2-0.4 mg / ml.

7. The method of claim 1 wherein The transparent conductive substrate material is indium tin oxide or fluorine-doped tin oxide.

8. The Nb2C coated on the surface of the transparent conductive substrate material prepared by the preparation method of any one of claims 1-7 x - MXene nanoplatelet hole injection layer material with a light transmittance greater than 98%.

9. The Nb2C T of claim 8 x Use of MXene nanoplatelet hole injection layer materials in the preparation of OLEDs devices.

10. The Nb2C of claim 8 x Use of MXene nanoplatelet hole injection layer materials in the preparation of solar cells or photodetector devices.

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