Few-layered tiO2-mxene composite material, and preparation method and application thereof

Abstract

A preparation method of a few-layer TiO2-MXene composite material, comprising a hydrothermal reaction step, the hydrothermal reaction step is specifically: mixing thin-layer MXene colloid with concentrated hydrochloric acid to form a pre-reaction mixture, carrying out hydrothermal reaction on the pre-reaction mixture to form a final reaction mixture, so that granular TiO2 nanocrystals are in-situ grown on the MXene, and the TiO2 nanocrystals contain rutile TiO2 crystal form; the present application adopts one-step hydrothermal reaction to generate TiO2 nanocrystals in-situ grown on the MXene, before the hydrothermal reaction, concentrated hydrochloric acid is mixed into the MXene, which is beneficial to control the TiO2 nanocrystals to be granular, due to the presence of concentrated hydrochloric acid, the generation of rutile titanium dioxide crystal form is promoted, the structure of TiO2-MXene is more stable, the agglomeration problem of TiO2-MXene is reduced, and a few-layer TiO2-MXene composite material is also provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material preparation, in particular to a few-layer TiO2-MXene composite material and a preparation method and application thereof. BACKGROUND

[0002] The electron transport layer plays an important role in the performance of perovskite solar cell devices. For photo-generated electrons from the perovskite layer, the electron transport layer provides a good transport path, while preventing the electrons on the transparent electrode from recombining with the holes from the perovskite layer. In general, the selection of the electron transport layer can be guided by the following requirements: (1) excellent carrier mobility, which is conducive to the efficient transport of electrons; (2) stable chemical properties, which will not cause chemical reactions that destroy the ITO electrode and the perovskite layer; (3) good energy level matching, with a LUMO slightly lower than or equal to the LUMO of the perovskite material, and a HOMO lower than the HOMO of the perovskite layer.

[0003] n-type metal oxide semiconductors such as TiO2 and SnO2 are common materials for preparing perovskite electron transport layers, and TiO2 is the most common material for preparing electron transport layers due to its good energy level matching with perovskite, stable chemical properties, rich morphology, and non-toxic and low cost. For efficient PSCs, photo-generated carriers in the perovskite layer and the charge transport layer should be quickly and effectively separated and extracted. However, starting from TiO2 and SnO2, their poor electron mobility, even much lower than the common hole mobility, will result in ineffective electron transport and accumulation at the interface, and recombination with holes from the perovskite layer, leading to a decrease in device performance.

[0004] Graphene-like 2D material MXene and its derivatives are considered as promising electron transport layer materials due to their excellent electron mobility, good energy level matching with perovskite materials, and appropriate surface physical and chemical modification and adjustment of work function. The 2D structure of MXene provides a good channel for carrier transport in PSCs, thereby improving the phenomenon of charge recombination at defects. The 2D structure of MXene provides a good channel for carrier transport in PSCs, thereby improving the phenomenon of charge recombination at defects. The large number of terminal groups and Ti-O bonds on the surface of MXene also have a positive effect on the entire device. However, the characteristic of MXene layer structure is easy to agglomerate, which will cause the problem of island distribution of the transport layer and local short circuit. SUMMARY

[0005] Therefore, in view of the above problems, it is necessary to provide a preparation method of a few-layer TiO2-MXene composite material.

[0006] It is also necessary to provide a few-layer TiO2-MXene composite material.

[0007] A preparation method of a few-layer TiO2-MXene composite material, comprising a hydrothermal reaction step, wherein the hydrothermal reaction step is specifically:

[0008] Mixing the thin-layer MXene colloid with concentrated hydrochloric acid to form a pre-reaction mixture, wherein the volume ratio of MXene colloid to concentrated hydrochloric acid is 50-100;

[0009] Performing hydrothermal reaction on the pre-reaction mixture, wherein the hydrothermal reaction temperature is controlled at 110-130℃, to form a final reaction mixture, so as to grow granular TiO2 nanocrystals on MXene in situ, wherein the TiO2 nanocrystals contain rutile TiO2 crystal form;

[0010] Filtering the final reaction mixture to obtain a few-layer TiO2-MXene composite material.

[0011] Preferably, the hydrothermal reaction temperature is controlled at 120℃, and the hydrothermal reaction time is 6h.

[0012] Preferably, the mass fraction of the concentrated hydrochloric acid is 36%.

[0013] Preferably, the particle size of the TiO2 nanocrystals is 30-50nm.

[0014] Preferably, the preparation method of the few-layer TiO2-MXene composite material further comprises an ultrasonic dispersion step, wherein the ultrasonic dispersion step is specifically:

[0015] Dispersing MXene powder into deionized water and performing ultrasonic treatment for 60-75min, then centrifugal separation and collecting the upper turbidity to obtain a thin-layer MXene colloid.

[0016] Preferably, the preparation method of the few-layer TiO2-MXene composite material further comprises an etching step, wherein the etching step is specifically:

[0017] Mixing MAX, lithium fluoride and hydrochloric acid with a mass fraction of 8-10% according to a predetermined ratio to form a pre-etching mixture;

[0018] Stirring the pre-etching mixture at 30-50℃ to perform continuous etching to obtain layered material MXene.

[0019] Washing the layered material MXene to pH=6-7, then drying and grinding to obtain MXene powder.

[0020] Preferably, the MAX is Ti3AlC2.

[0021] Preferably, the particle size of the MAX is 325 mesh.

[0022] A few-layer TiO2-MXene composite material is obtained by the preparation method of the few-layer TiO2-MXene composite material.

[0023] Preferably, the application of the few-layer TiO2-MXene composite material as an electron transport layer of a perovskite solar cell.

[0024] Compared with the prior art, the present application adopts one-step hydrothermal reaction to generate TiO2 nanocrystals in situ grown on MXene, and before the hydrothermal reaction, concentrated hydrochloric acid is mixed into the MXene, which is beneficial to control the TiO2 nanocrystals into granular shape, can effectively solve the agglomeration problem of TiO2-MXene, and at the same time, due to the presence of concentrated hydrochloric acid, can promote the generation of rutile titanium dioxide crystal type, so that the structure of TiO2-MXene is more stable, and the agglomeration problem of TiO2-MXene is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The XRD pattern of the TiO2-MXene composite material.

[0026] Figure 2 The SEM image of the TiO2-MXene composite material.

[0027] Figure 3 The wetting angle of the electron transport layer of different materials, wherein (a) is TiO2-MXene, (b) is MXene, and (c) is TiO2.

[0028] Figure 4 The J-V curve and external quantum efficiency of TiO2, MXene and TiO2-MXene.

[0029] Figure 5 The encapsulated device PCE of TiO2, MXene and TiO2-MXene changes with time.

[0030] Figure 6 The PL and TRPL spectra of the perovskite thin film prepared based on TiO2, MXene and TiO2-MXene. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will be further described in combination with the embodiments.

[0032] The embodiment of the present application provides a preparation method of a few-layer TiO2-MXene composite material, which comprises a hydrothermal reaction step, and the hydrothermal reaction step is specifically:

[0033] mixing the thin-layer MXene colloid with concentrated hydrochloric acid to form a pre-reaction mixture, wherein the volume ratio of the thin-layer MXene colloid to the concentrated hydrochloric acid is 50-100;

[0034] performing a hydrothermal reaction on the pre-reaction mixture to form a final reaction mixture, wherein the hydrothermal reaction temperature is controlled at 110-130 DEG C, so as to grow the granular TiO2 nanocrystals on the MXene in-situ, and the TiO2 nanocrystals contain the rutile TiO2 crystal form;

[0035] filtering the final reaction mixture to obtain the few-layer TiO2-MXene composite material.

[0036] "Thin layer" or "few layers" are relative to "multi-layer" and "single layer", and for the thicker multi-layer material, after etching and thinning, the number of layers is between "multi-layer" and "single layer", which can be called "thin layer" or "few layers".

[0037] For example, 50 mL of the thin-layer MXene colloid is placed in a high-temperature reaction kettle, and 0.5 mL of hydrochloric acid with a mass fraction of 36% is added dropwise, and then the mixture is placed in an oven for 6 h at 120 DEG C.

[0038] Further, the final reaction mixture is filtered and washed to pH = 6-7 using a sand core funnel, and then freeze-dried to obtain the few-layer TiO2-MXene composite material.

[0039] Titanium dioxide has two crystal forms, namely anatase titanium dioxide and rutile titanium dioxide, wherein the rutile titanium dioxide is more stable.

[0040] Compared with the prior art, the present application adopts one-step hydrothermal reaction to generate TiO2 nanocrystals grown in-situ on MXene, and before the hydrothermal reaction, concentrated hydrochloric acid is mixed into the MXene, which is beneficial to control the TiO2 nanocrystals to be granular, and can effectively solve the agglomeration problem of TiO2-MXene, and at the same time, due to the presence of concentrated hydrochloric acid, the generation of rutile titanium dioxide crystal form is promoted, and excessive oxidation is prevented, so that the structure of TiO2-MXene is more stable, and the agglomeration problem of TiO2-MXene is reduced.

[0041] Further, the hydrothermal reaction temperature is controlled at 120 DEG C, and the hydrothermal reaction time is 6 h.

[0042] Further, the mass fraction of the concentrated hydrochloric acid is 36%.

[0043] Further, the particle size of the TiO2 nanocrystals is 30-50 nm.

[0044] Further, the preparation method of the few-layer TiO2-MXene composite material further comprises an ultrasonic dispersion step, and the ultrasonic dispersion step specifically comprises:

[0045] Disperse MXene powder into deionized water and perform ultrasonic treatment for 60-75 min, then centrifugal separation and collect the upper turbidity to obtain thin-layer MXene colloid.

[0046] Centrifugal separation is performed by a centrifuge for 60 min, and the centrifuge speed should not exceed 3500 rpm / min.

[0047] Further, the preparation method of the few-layer TiO2-MXene composite material further comprises an etching step, and the etching step specifically comprises:

[0048] Mix MAX, lithium fluoride and hydrochloric acid with a mass fraction of 8-10% according to a predetermined ratio to form a pre-etching mixture;

[0049] Stir the pre-etching mixture at 30-50℃ to perform continuous etching, and obtain layered material MXene.

[0050] Wash the layered material MXene to pH=6-7, then dry and grind to obtain MXene powder.

[0051] For example, mix 1g of MAX with 15-20mL of hydrochloric acid and 1g of lithium fluoride in a polytetrafluoroethylene beaker, heat to room temperature of 30-50℃ by a magnetic stirrer, and perform continuous etching at a rotation speed of 120-3000prm / min for 48h. After etching is completed, for the acidic mixture, repeatedly wash by a centrifuge with a rotation speed of 8000rpm / min and each cycle of 5min until pH=6-7, place the obtained sample in an oven for drying at 60℃, and grind and collect.

[0052] Further, the MAX is Ti3AlC2.

[0053] Further, the particle size of the MAX is 325 mesh.

[0054] The few-layer TiO2-MXene composite material is obtained by the preparation method of the few-layer TiO2-MXene composite material.

[0055] Further, the few-layer TiO2-MXene composite material is applied as an electron transport layer of a perovskite solar cell.

[0056] The present application is further illustrated by the following examples and comparative examples, and the following examples are only used to illustrate the present application in detail, and do not limit the protection scope of the present application in any way.

[0057] Example 1: 1 g of MAX was mixed with 15 mL of hydrochloric acid (mass fraction 8-10%) and 1 g of lithium fluoride into a polytetrafluoroethylene beaker, heated to room temperature about 45°C by a magnetic stirrer, and continuously etched at a speed of 230 prm / min for 48 h; after etching, the acid mixture was repeatedly washed with deionized water to PH = 6-7 by a centrifuge at a speed of 8000 rpm / min for 5 min each cycle, and the obtained sample was placed in an oven for drying at 60°C, ground and collected to obtain MXene powder; the MXene powder was dispersed in deionized water and ultrasonically treated for 60-75 min, then centrifuged at 3500 rpm / min for 60 min, after centrifugation, the upper turbid liquid was collected to obtain a thin-layer MXene colloid; 50 mL of the thin-layer MXene colloid was taken into a high-temperature reaction kettle, and 0.5 mL of hydrochloric acid with a mass fraction of 36% was added dropwise, and then placed in an oven at 120°C for 6 h to obtain a final reaction mixture, which was filtered and washed to pH = 6-7 using a sand core funnel, and then freeze-dried to obtain a few-layer TiO2-MXene composite material.

[0058] Referring to Figure 1 A new peak appeared at 25.31°, corresponding to the (101) plane of A-TiO2, and the characteristic peak at 27.2° was the (110) plane of R-TiO2. A-TiO2 is anatase titanium dioxide, and R-TiO2 is rutile titanium dioxide.

[0059] Referring to Figure 2 The surface of the TiO2-MXene composite material has a large number of TiO2 small particles generated, and the dispersion is good and no agglomeration phenomenon occurs.

[0060] Referring to Figure 3 The contact angles of TiO2, MXene and TiO2-MXene are 77.3°, 55.7° and 45.3°, respectively. The TiO2-MXene composite material has the smallest wetting angle, so it has the best wettability, which is conducive to reducing the nucleation energy of perovskite, thereby promoting the formation of a dense and good perovskite thin film.

[0061] The ΔG of TiO2 (77.3°), MXene (55.7°), and TiO2-MXene (45.3°) are -0.0878, -0.1125, and -0.1226 J·m -1From the perspective of thermodynamics, a lower ΔG will enhance the ability of the thin film to adsorb steam molecules, and in the preparation of perovskite thin films, the solution can better adsorb and spread on the electron transport layer, thereby facilitating the formation of a dense and good perovskite thin film, greatly reducing the internal defects of the thin film. This means that the perovskite photoactive layer has better light trapping ability, and the reduction of internal defects also helps to reduce the problem of carrier recombination and perovskite degradation caused by defects, thereby effectively improving the efficiency and stability of the device.

[0062] Example 2: The perovskite solar cell is prepared as follows:

[0063] ITO conductive glass cleaning: Select a conductive glass with a size of 1.5 cm x 1.5 cm, first clean the surface of the attached object with alcohol and deionized water, and then wipe it with a dust-free cloth. Put the wiped conductive glass sheet into the cleaning rack and put it into a beaker, then use deionized water, acetone and isopropanol for ultrasonic cleaning for 45 min, finally, use an air gun to blow dry the glass sheet, and put it into a glass dish with the front face up.

[0064] Preparation of electron transport layer: The ITO conductive glass is subjected to ultraviolet treatment for 15-30 min to improve its wettability, and is subjected to spin coating within 2 h, with spin coating parameters of 3000 rpm, 30 s. Use a pipette to suck 60 μL of electron transport layer solution and vertically drop it onto the glass surface for spin coating film formation. Place the spin-coated sample on a constant temperature platform and anneal at 150°C for 30 min to form a dense electron transport layer. The electron transport layer solution is a dispersion of the above-mentioned few-layer TiO2-MXene composite material.

[0065] Preparation of PbI2 solution: Weigh 591.5 mg of PbI2 and 15.6 mg of CsCl, mix them together and dissolve them in 800 mL of DMF + 200 mL of DMSO mixed solution. Stir at 70°C for 2 h, then filter with a 0.22 μm polytetrafluoroethylene filter head and wait for use.

[0066] Preparation of organic salt solution: Weigh 90 mg of FAI, 4 mg of MABr and 9 mg of MACI, mix them together and dissolve them in 1 mL of isopropanol (IPA) solution. Stir at room temperature for 30 min, then filter with a 0.22 μm polytetrafluoroethylene filter head and wait for use.

[0067] Perovskite layer preparation: the electron transport layer formed by film was subjected to ultraviolet treatment for 15-30 min, then the spin coating of PbI2 solution was performed on the electron transport layer in the glove box at the parameters of 2500 rpm, 30 s and immediately placed on the constant temperature heating plate, and then removed after annealing at 70℃ for 60 s; after cleaning the glove box for 15-20 min, 65 μL of the organic salt solution was spin-coated under the conditions of 1500 rpm, 30 s, and the spin coating switch was immediately opened when the organic salt solution spread from the center of the glass to the periphery; the glove box was immediately removed after spin coating, and annealed on the constant temperature heating plate at 150℃ for 20 min.

[0068] Preparation of Spiro-OMeTAD solution: 72.3 mg of Spiro-OMeTAD powder was dissolved in 1 mL of chlorobenzene (CB), and then 17.5 μL of lithium salt acetonitrile solution (520 mg / mL) and 28.8 μL of 4-tBP solution were measured with a pipette; the above solution was ultrasonicated in an ultrasonic instrument for 5 min and then filtered with a 0.22 μm polytetrafluoroethylene filter head for use.

[0069] Preparation of hole transport layer: 65 μL of filtered Spiro solution was spin-coated on the perovskite layer under the parameter conditions of 3000 rpm for 30 s to form a film.

[0070] Evaporation of metal electrode: a 600-900 Å thick gold layer was deposited on the Spiro-OMeTAD layer as a counter metal electrode by vacuum evaporation, thereby obtaining a complete perovskite solar cell.

[0071] Figure 4 The TiO 2、 The results of the photoelectric performance test of the electron transport layer made of MXene, TiO2-MXene and TiO2-MXene. The photoelectric performance of TiO2-MXene is the best, and its short-circuit current, open-circuit voltage, fill factor and photoelectric conversion efficiency are better than those of other materials, respectively: open-circuit voltage VOC is 10.32 mA·cm-2, short-circuit current JSC is 16.8 mA·cm-2, photoelectric conversion efficiency is 12.5%, and EQE is 83.6%.

[0072] Referring to Figure 5 After the PSC devices based on TiO2, MXene and TiO2-MXene were exposed to the natural environment for 384 h, their efficiencies decreased to 78.1%, 56.4% and 61.2% of the initial efficiency, respectively. When MXene material is used as ETL, it will present island-like distribution, resulting in direct contact between the perovskite layer and the ITO conductive glass and causing local short circuit phenomenon, which reduces the stability of the device, while TiO2-MXene material is relatively dense, reducing the short circuit phenomenon.

[0073] Referring to Figure 6 The photoluminescence intensity decay of the perovskite thin film based on different electron transport layers presents the phenomenon of TiO2-MXene > MXene > TiO2;the perovskite thin film formed on the TiO2-MXene has a fast electron injection rate, and the electron injection lifetime is 56.2 ns, and the charge extraction efficiency is the highest.

[0074] The synthesized few-layer TiO2-MXene composite material has excellent performance as an electron transport layer material of PSCs, and TiO2 nanocrystals are in-situ grown on the MXene through a one-step hydrothermal method. The Ti-O bond generated by oxidation in the TiO2-MXene can effectively reduce the macroscopic defects of the spin-coated film, and has better wettability, and lower Gibbs free energy, which is beneficial to the formation of a dense perovskite thin film. O2 The TiO2-MXene electron transport layer promotes the crystallization of the perovskite layer and obtains a uniform and large grain size, and the large grain size is beneficial to the perovskite crystal to better absorb light.

[0075] The steps in the method of the embodiments of the present application can be adjusted in sequence, combined and deleted according to actual needs.

[0076] The above disclosure is only the preferred embodiments of the present application, and of course cannot limit the scope of the rights of the present application, and those skilled in the art can understand that all or part of the above-mentioned embodiments are implemented, and equivalent changes made according to the claims of the present application still belong to the scope covered by the present application.

Claims

1. The application of a few-layer TiO2-MXene composite material as the electron transport layer of a perovskite solar cell, characterized in that: The preparation method of the few-layer TiO2-MXene composite material includes a hydrothermal reaction step, wherein the hydrothermal reaction step specifically comprises: Thin-layer MXene colloid is mixed with concentrated hydrochloric acid to form a pre-reaction mixture. The volume ratio of MXene colloid to concentrated hydrochloric acid is 50-100. The pre-reaction mixture is subjected to a hydrothermal reaction at a temperature controlled at 110-130°C to form a final reaction mixture, thereby enabling the in-situ growth of particulate TiO2 nanocrystals on MXene, wherein the TiO2 nanocrystals contain rutile TiO2 crystal form. The final reaction mixture was filtered to obtain a few-layer TiO2-MXene composite material; The concentrated hydrochloric acid has a mass fraction of 36%. The preparation method of the few-layer TiO2-MXene composite material further includes an ultrasonic dispersion step, which specifically includes: MXene powder was dispersed in deionized water and sonicated for 60-75 minutes. Then, it was centrifuged and the supernatant was collected to obtain a thin layer of MXene colloid. The preparation method of the few-layer TiO2-MXene composite material further includes an etching step, which specifically includes: MAX, lithium fluoride and hydrochloric acid with a mass fraction of 8-10% are mixed in a predetermined ratio to form a pre-etching mixture; The pre-etching mixture is stirred at 30-50°C to perform continuous etching, thereby obtaining the layered material MXene; The layered material MXene was washed to pH 6-7, then dried and ground to obtain MXene powder; The electron transport layer was prepared by subjecting the ITO conductive glass to UV treatment for 15-30 minutes to improve its wettability, and then spin-coating it using a spin coater within 2 hours at 3000 rpm for 30 seconds. 60 μL of the electron transport layer solution was pipetted and vertically dropped onto the glass surface to form a film. The spin-coated sample was then placed on a constant temperature platform and annealed at 150°C for 30 minutes to form a dense electron transport layer. The electron transport layer solution was a dispersion of the aforementioned few-layer TiO2-MXene composite material.

2. The application of the few-layer TiO2-MXene composite material as described in claim 1 as the electron transport layer of a perovskite solar cell, characterized in that: The hydrothermal reaction temperature was controlled at 120℃, and the hydrothermal reaction time was 6 hours.

3. The application of the few-layer TiO2-MXene composite material as described in claim 1 as the electron transport layer of a perovskite solar cell, characterized in that: The TiO2 nanocrystals have a particle size of 30-50 nm.

4. The application of the few-layer TiO2-MXene composite material as described in claim 1 as the electron transport layer of a perovskite solar cell, characterized in that: The MAX is Ti3AlC2.

5. The application of the few-layer TiO2-MXene composite material as described in claim 1 as the electron transport layer of a perovskite solar cell, characterized in that: The particle size of the MAX is 325 mesh.

6. A few-layer TiO2-MXene composite material, characterized in that: It is obtained by the preparation method of the few-layer TiO2-MXene composite material according to claim 1.

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