A composite film with piezoelectric-photoelectric function and its preparation method and application

Abstract

The present invention belongs to the field of flexible sensor technology, and specifically relates to a composite film with piezoelectric-photoelectric functions, and its preparation method and application. The composite film with piezoelectric-photoelectric functions includes two piezoelectric layers and a multifunctional layer located between the two piezoelectric layers, wherein the piezoelectric layer is polyvinylidene fluoride or a polyvinylidene fluoride copolymer; and the multifunctional layer is a TiO2@photosensitive dye molecular nanoheterojunction. The present invention utilizes the piezoelectric effect and photoelectric effect of the composite film to realize the tactile perception and light perception functions of the sensor. This method of realizing the multifunctionality of the device by relying on the multifunctionality of the material eliminates the tedious integration process of the device and the complex auxiliary electronic system, reduces the production cost, and is suitable for large-scale production applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and in particular relates to a composite film with piezoelectric-photoelectric functions, a preparation method thereof, and applications thereof. Background Art

[0002] Touch is an important sensory pathway for humans to understand the outside world, and tactile sensors are also an important means for machines to interact and perceive humans and the outside world. With the continued advancement of intelligent systems such as robotics, human-computer interaction, biomedicine, and wearable electronic devices in production and life, people's requirements for tactile sensors are becoming increasingly higher, and higher requirements are also being placed on the functionality of sensors. The demand for new flexible tactile sensors is also increasing. Based on different operating principles, flexible tactile sensors can be divided into piezoelectric sensors, piezoresistive sensors, capacitive sensors, electromagnetic sensors, and triboelectric sensors. Among them, flexible tactile sensors based on the piezoelectric effect have the advantage of not requiring an external power supply, overcoming the obstacles of integrating an additional power supply, and have become one of the most popular pressure sensors in the research field.

[0003] Polyvinylidene fluoride (PVDF) and its copolymers (PVDF-HFP and PVDF-TrFE) are semicrystalline polymers whose electroactivity is determined by the piezoelectric phase (i.e., β-phase) of the TTTT conformation. These polymers possess advantages such as high flexibility, strong electromechanical coupling, good biocompatibility, and a wide response range, making them promising for applications requiring a certain degree of flexibility, such as wearables. To increase the piezoelectric phase content in PVDF, particle-induced polarization (PIP) is an effective method. This involves embedding nanoparticles, such as carbon quantum dots (CQDs), BaTiO3, carbon black, ZnO, graphene, and carbon nanotubes (CNTs), into PVDF. The induced active sites, surface charge, and local electric field on the nanoparticles' surfaces interact with the PVDF dipoles, promoting the formation of the piezoelectric phase during material formation, resulting in flexible piezoelectric materials with excellent performance. For example, Si Wenyan et al. (Preparation and pressure sensing of ZnO / PVDF composite micron fiber arrays produced by low-voltage near-field electrospinning. Journal of Chemistry of Universities. 2017, 38(6):997-1001) used near-field electrospinning to embed ZnO particles into PVDF to obtain ZnO / PVDF composite micron fiber arrays and demonstrated the piezoelectric effect of the composite material. Zhang Yike et al. (Preparation and piezoelectric properties of carbon nanotube / polyvinylidene fluoride nanofiber membranes. Journal of Textile Research. 2021, 42(3):44-50) used electrospinning to introduce CNTs into PVDF nanofiber membranes to prepare CNTs / PVDF nanofiber membranes and assembled them into a flexible piezoelectric sensor with a sandwich structure. The above studies only improved the piezoelectric performance of the sensors, resulting in low sensitivity, single function, and a narrow range of applications. In order to expand the scope of application of flexible piezoelectric sensors, it is urgent to develop a flexible piezoelectric sensor that integrates multiple functions such as piezoelectricity, mechanical properties, and optical properties. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, one of the purposes of the present invention is to provide a composite film with piezoelectric-photoelectric functions. The composite film has a sandwich structure. While maintaining high flexibility and self-power supply, the film material is endowed with photoelectric properties by means of an intermediate multifunctional layer.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A composite film with piezoelectric-photoelectric functions includes two piezoelectric layers and a multifunctional layer located between the two piezoelectric layers; the piezoelectric layers are polyvinylidene fluoride (PVDF) or polyvinylidene fluoride copolymers (PVDF-HFP or PVDF-TrFE); and the multifunctional layer is a TiO2@photosensitive dye molecular nanoheterojunction.

[0007] As a preferred embodiment of the above technical solution, the thickness of the piezoelectric layer is 10-100 μm, and the thickness of the multifunctional layer is 0.1-5 μm. Preferably, the thickness of the piezoelectric layer is 10-50 μm, and the thickness of the multifunctional layer is 0.5-3.5 μm.

[0008] In dye-sensitized solar cells, the TiO2 photoanode, along with the photosensitizing dye adsorbed on its surface (i.e., the TiO2@photosensitive dye molecule nanoheterojunction structure), captures sunlight and generates and separates excitons (electron-hole pairs). Simultaneously, the photosensitizing dye molecules are adsorbed as a monolayer on the TiO2 surface, forming a relatively stable chemical bond between the two, resulting in a stable photoelectric effect. Inspired by this, the inventors introduced the TiO2@photosensitive dye molecule nanoheterojunction structure into piezoelectric materials. This not only compensates for the lack of surface functional groups and weak interfacial bonding on the TiO2 particles, but also stimulates the inductive and interfacial bridging effects of the piezoelectric phase nanoparticles, endowing the material with stable photoelectric properties.

[0009] The present invention further provides a method for preparing the above-mentioned composite film having piezoelectric-photoelectric functions, comprising the following steps:

[0010] (1) Preparation of piezoelectric layer solution:

[0011] Dissolving polyvinylidene fluoride or polyvinylidene fluoride copolymer in an organic solvent at a mass ratio of 1:(5-10) to obtain a piezoelectric layer solution;

[0012] (2) Preparation of multifunctional layer solution:

[0013] S1. Preparation of photosensitizing dye solution: Add photosensitizing dye to ethanol at a mass ratio of 1:(1000-2000), and stir at 30-50°C for 18-30 hours to obtain a photosensitizing dye solution;

[0014] S2. Preparation of TiO2 slurry: Add PEG-20000 to water at a mass ratio of 1:(5-10), stir and dissolve to obtain a PEG-20000 solution; then add TiO2 powder, acetylacetone, and ethanol to the PEG-20000 solution and alternately mix to obtain a TiO2 dispersion; finally, uniformly mix the TiO2 dispersion with Triton X100 solution at a mass ratio of 1:(0.05-0.1), and ball mill for 60-120 minutes to obtain a TiO2 slurry;

[0015] Among them, the mass ratio of TiO2 powder, acetylacetone, ethanol, and PEG-20000 solution is 1: (0.2~0.5): (0.2~0.5): (4~8);

[0016] S3. Preparation of a multifunctional layer solution: TiO2 slurry is coated on glass and subjected to a series of heat treatments to obtain a TiO2 porous membrane. The TiO2 porous membrane is then immersed in a photosensitizing dye solution and allowed to stand in the dark for 18 to 30 hours. After the solution is removed, washed, dried, and separated from the glass to obtain TiO2@photosensitive dye molecular powder. Finally, the TiO2@photosensitive dye molecular powder is added to ethanol at a mass ratio of 1:(1000-2000) and mixed uniformly to obtain a multifunctional layer solution.

[0017] (3) Preparation of composite films:

[0018] The piezoelectric layer solution is coated on the conductive surface of the ITO-PEN electrode and dried to form a piezoelectric layer. The multifunctional layer solution is then coated on the surface of the piezoelectric layer and dried to form a multifunctional layer. Finally, the piezoelectric layer solution is coated on the surface of the multifunctional layer and heat treated to form a piezoelectric layer, thereby obtaining a composite film with piezoelectric-photoelectric functions on the surface of the ITO-PEN electrode.

[0019] As a preferred embodiment of the above technical solution, in step (1), the organic solution is one or more of N,N-dimethylformamide, acetone, ethanol, cyclohexane, ethyl acetate, and chloroform.

[0020] Preferably, the organic solvent is a mixed solvent consisting of N,N-dimethylformamide and acetone in a mass ratio of 1:(0.5~1).

[0021] As a preferred embodiment of the above technical solution, in S1 of step (2), the photosensitizing dye is any one of N719 dye, N3 dye, coumarin, porphyrin, polymethine, carotenoid, perylene, anthocyanin, hemicyanin, pterostilbene, and chlorophyll.

[0022] As a preferred embodiment of the above technical solution, in S2 of step (2), the average particle size of the TiO2 powder is 10-50 nm; the alternating mixing refers to first magnetic stirring for 15-30 minutes, then ultrasonic stirring for 15-30 minutes, and this as one cycle, and 6-10 cycles are performed; the Triton X100 solution is obtained by dissolving Triton X100 in water at a volume ratio of 1:(10-20).

[0023] As a preferred embodiment of the above technical solution, in step (2) S3, the coating is carried out by any one of spin coating, scraper coating, screen printing or casting; the stepwise heat treatment refers to first keeping the temperature at 50-60°C for 30-60 minutes, then keeping the temperature at 100-120°C for 5-15 minutes, and finally keeping the temperature at 400-500°C for 20-40 minutes.

[0024] As a preferred embodiment of the above technical solution, in step (3), the coating is carried out by any one of spin coating, scraper coating, screen printing or casting, preferably spin coating, with a spin coating speed of 1000~3000rpm and a time of 30~120s; the drying is carried out by keeping the temperature at 30~60℃ for 5~20min; the heat treatment refers to keeping the temperature at 30~60℃ for 20~40min and then keeping the temperature at 100~130℃ for 0.5~2h.

[0025] Another object of the present invention is to provide an application of the above-mentioned composite film with piezoelectric-photoelectric functions in a multifunctional flexible piezoelectric sensor.

[0026] The method for preparing the multifunctional flexible piezoelectric sensor comprises the following steps:

[0027] The ITO-PEN electrode of the above-mentioned composite film with piezoelectric-photoelectric function is placed face up, and then another blank ITO-PEN electrode is taken with the conductive surface facing down, and the upper surface is staggered and covered. The uncovered parts of the two electrodes are used as leads, and silicone is coated around them for fixation. The wires are fixed to the two electrode leads with conductive silver paste to obtain the multifunctional flexible piezoelectric sensor.

[0028] In summary, the present invention has the following beneficial effects:

[0029] 1. The present invention introduces the TiO2@photosensitive dye molecule nanoheterojunction structure into the piezoelectric material, which not only makes up for the shortcomings of insufficient functional groups on the surface of TiO2 particles and weak interface bonding, but also greatly stimulates the piezoelectric phase nanoparticle induction effect and interface bridging effect. Moreover, the particle induction effect enhanced by the nanoheterojunction structure can promote the formation of the piezoelectric phase of polyvinylidene fluoride in the piezoelectric layer. The enhanced interface bridging effect between the photosensitive dye molecules of TiO2 particles and the polyvinylidene fluoride substrate can improve the interface stress transfer. At the same time, the photosensitive dye molecules are in a single-layer adsorption state on the TiO2 surface, playing the role of capturing sunlight and generating and separating excitons (electron-hole pairs), thereby generating a stable photoelectric effect. Therefore, the composite film prepared by the present invention has both excellent flexibility and piezoelectric properties, as well as stable photoelectric properties.

[0030] 2. The present invention adopts the technology of adsorbing photosensitive molecules on TiO2 solid film in the process of preparing the multifunctional layer solution, avoiding the multilayer adsorption of photosensitive molecules on the TiO2 surface, thereby obtaining a TiO2@photosensitive dye molecule nanoheterojunction structure with a single molecular layer of photosensitive molecules adsorbed. This not only ensures the excitation of the multilayer effect of the nanoheterojunction structure, but also reduces the material cost.

[0031] 3. The present invention utilizes the piezoelectric effect and photoelectric effect of the composite film to realize the tactile perception and light perception functions of the sensor. This method of realizing the multifunctionality of the device by leveraging the multifunctionality of the material eliminates the tedious integration process and complex auxiliary electronic system of the device, reduces production costs, and is suitable for large-scale production applications.

[0032] 4. The multifunctional flexible piezoelectric sensor fabricated by this invention has significant application value in intelligent systems such as wearable electronics, intelligent robots, human-machine interaction, and human health measurement. For example, when used as electronic skin for intelligent robots, it enhances tactile perception while also providing new light sensing capabilities. Furthermore, excess energy captured by the sensor can be used by other electronic devices within the intelligent system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic structural diagram of the multifunctional flexible piezoelectric sensor of Example 1;

[0034] Figure 2 is a SEM image of the intermediate product in Example 1 - the TiO2 porous membrane;

[0035] Figure 3 is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 under periodic constant force;

[0036] Figure 4 is the real-time output voltage-force curve of the multifunctional flexible piezoelectric sensor in Example 1;

[0037] Figure 5 is the real-time output current-force curve of the multifunctional flexible piezoelectric sensor in Example 1;

[0038] Figure 6 is a real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 under continuous bending and torsion working conditions;

[0039] Figure 7 This is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 when it is placed on the ground and stepped on by the foot;

[0040] Figure 8 is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 under simulated continuous wind blowing;

[0041] Figure 9 This is the real-time output voltage-time curve of the flexible piezoelectric sensor in comparative example 1 under periodic constant force;

[0042] Figure 10This is the real-time output voltage-force curve of the flexible piezoelectric sensor in Example 1 under periodic constant force. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below with reference to specific embodiments. However, the specific details of the embodiments are only for the purpose of illustrating the present invention and do not represent all the technical methods under the concept of the present invention. Therefore, they should not be understood as limiting the overall technical solution of the present invention.

[0044] Example 1

[0045] A method for preparing a multifunctional flexible piezoelectric sensor comprises the following steps:

[0046] (1) Preparation of piezoelectric layer solution:

[0047] N,N-dimethylformamide and acetone were mixed uniformly at a mass ratio of 1:0.55 to obtain a mixed solvent, and then PVDF-HFP was dissolved in the mixed solvent at a mass ratio of 1:6.32 to obtain a piezoelectric layer solution;

[0048] (2) Preparation of multifunctional layer solution:

[0049] S1. Preparation of photosensitizing dye solution: Add photosensitizing dye N719 to ethanol at a mass ratio of 1:1330, and stir at 40°C for 24 hours to obtain a photosensitizing dye solution;

[0050] S2. Preparation of TiO2 slurry: PEG-20000 was added to deionized water at a mass ratio of 1:9.38, and stirred to dissolve to obtain a PEG-20000 solution. TiO2 powder, acetylacetone, and ethanol were then added to the PEG-20000 solution, and alternately mixed to obtain a TiO2 dispersion. Finally, the TiO2 dispersion was uniformly mixed with a Triton X100 solution at a mass ratio of 1:0.06, and ball milled for 60 minutes to obtain a TiO2 slurry.

[0051] The mass ratio of TiO2 powder, acetylacetone, ethanol, and PEG-20000 solution is 1:0.49:0.2:4.15 by weight; the average particle size of the TiO2 powder is 25 nm; the alternating mixing refers to first magnetic stirring for 30 minutes, then ultrasonic stirring for 15 minutes, and this is one cycle, and 6 cycles are performed; the Triton X100 solution is obtained by dissolving Triton X100 in water at a volume ratio of 1:10.

[0052] S3. Preparation of a multifunctional layer solution: Spin-coat a TiO2 slurry onto glass and obtain a TiO2 porous membrane after a series of heat treatments. Then, immerse the TiO2 porous membrane in a photosensitizing dye solution and allow it to stand in the dark for 24 hours. After the solution is complete, remove the membrane, wash it, dry it, and separate it from the glass to obtain TiO2@photosensitive dye molecular powder. Finally, add the TiO2@photosensitive dye molecular powder to ethanol at a mass ratio of 1:1578 and mix them evenly to obtain a multifunctional layer solution.

[0053] The stepwise heat treatment is performed at 60°C for 30 minutes, then at 120°C for 5 minutes, and finally at 450°C for 30 minutes.

[0054] (3) Preparation of composite films:

[0055] The piezoelectric layer solution is spin-coated on the conductive surface of the ITO-PEN electrode to form a piezoelectric layer after drying. The multifunctional layer solution is then spin-coated on the surface of the piezoelectric layer to form a multifunctional layer after drying. Finally, the piezoelectric layer solution is spin-coated on the surface of the multifunctional layer again and heat-treated to form a piezoelectric layer, thereby obtaining a composite film with piezoelectric-photoelectric functions on the surface of the ITO-PEN electrode. The thickness of the piezoelectric layer is 44 μm, and the thickness of the multifunctional layer is 2.2 μm.

[0056] The spin coating was performed at a speed of 1000 rpm for 60 seconds. The drying step was performed at 60° C. for 10 minutes. The heat treatment step was performed at 30° C. for 30 minutes and then at 120° C. for 1 hour.

[0057] (4) Preparation of sensor:

[0058] The ITO-PEN electrode of the above-mentioned composite film with piezoelectric-photoelectric function is placed face up, and then another blank ITO-PEN electrode is taken with the conductive surface facing down, and the upper surface is staggered and covered. The uncovered parts of the two electrodes are used as leads, and silicone is coated around them for fixation. The wires are fixed to the two electrode leads with conductive silver paste to obtain the multifunctional flexible piezoelectric sensor.

[0059] Example 2

[0060] A method for preparing a multifunctional flexible piezoelectric sensor comprises the following steps:

[0061] (1) Preparation of piezoelectric layer solution:

[0062] N,N-dimethylformamide and acetone are mixed uniformly at a mass ratio of 1:0.8 to obtain a mixed solvent, and then PVDF-HFP is dissolved in the mixed solvent at a mass ratio of 1:8 to obtain a piezoelectric layer solution;

[0063] (2) Preparation of multifunctional layer solution:

[0064] S1. Preparation of photosensitizing dye solution: Add photosensitizing dye N3 to ethanol at a mass ratio of 1:1000, and stir at 50° C. for 18 h to obtain a photosensitizing dye solution;

[0065] S2. Preparation of TiO2 slurry: PEG-20000 was added to deionized water at a mass ratio of 1:5.65, and stirred to dissolve to obtain a PEG-20000 solution. TiO2 powder, acetylacetone, and ethanol were then added to the PEG-20000 solution and alternately mixed to obtain a TiO2 dispersion. Finally, the TiO2 dispersion was uniformly mixed with a Triton X100 solution at a mass ratio of 1:0.05, and ball milled for 90 minutes to obtain a TiO2 slurry.

[0066] The mass ratio of TiO2 powder, acetylacetone, ethanol, and PEG-20000 solution is 1:0.2:0.35:5.32 by weight; the average particle size of the TiO2 powder is 25 nm; the alternating mixing refers to first magnetic stirring for 25 minutes, then ultrasonic stirring for 20 minutes, and this is one cycle, and 8 cycles are performed; the Triton X100 solution is obtained by dissolving Triton X100 in water at a volume ratio of 1:20.

[0067] S3. Preparation of a multifunctional layer solution: Spin-coat a TiO2 slurry onto glass and obtain a TiO2 porous membrane after a series of heat treatments. Then, immerse the TiO2 porous membrane in a photosensitizing dye solution and allow it to stand in the dark for 18 hours. After the solution is complete, remove the membrane, wash it, dry it, and separate it from the glass to obtain TiO2@photosensitive dye molecular powder. Finally, add the TiO2@photosensitive dye molecular powder to ethanol at a mass ratio of 1:1125 and mix them evenly to obtain a multifunctional layer solution.

[0068] The stepwise heat treatment is performed by first keeping the temperature at 55°C for 45 minutes, then keeping the temperature at 100°C for 10 minutes, and finally keeping the temperature at 400°C for 25 minutes.

[0069] (3) Preparation of composite films:

[0070] The piezoelectric layer solution is spin-coated on the conductive surface of the ITO-PEN electrode to form a piezoelectric layer after drying. The multifunctional layer solution is then spin-coated on the surface of the piezoelectric layer to form a multifunctional layer after drying. Finally, the piezoelectric layer solution is spin-coated on the surface of the multifunctional layer again and heat-treated to form a piezoelectric layer, thereby obtaining a composite film with piezoelectric-photoelectric functions on the surface of the ITO-PEN electrode. The thickness of the piezoelectric layer is 27 μm, and the thickness of the multifunctional layer is 1.9 μm.

[0071] The spin coating was performed at a speed of 3000 rpm for 30 seconds. The drying step was performed at 45° C. for 5 minutes. The heat treatment step was performed at 40° C. for 40 minutes and then at 100° C. for 2 hours.

[0072] (4) Preparation of sensor:

[0073] The ITO-PEN electrode of the above-mentioned composite film with piezoelectric-photoelectric function is placed face up, and then another blank ITO-PEN electrode is taken with the conductive surface facing down, and the upper surface is staggered and covered. The uncovered parts of the two electrodes are used as leads, and silicone is coated around them for fixation. The wires are fixed to the two electrode leads with conductive silver paste to obtain the multifunctional flexible piezoelectric sensor.

[0074] The output voltage of the multifunctional flexible piezoelectric sensor prepared in the embodiment of the present invention is 2.58V, and the linear relationship R 2 >0.977, sensitivity is 255mV / N.

[0075] Example 3

[0076] A method for preparing a multifunctional flexible piezoelectric sensor comprises the following steps:

[0077] (1) Preparation of piezoelectric layer solution:

[0078] N,N-dimethylformamide and acetone are mixed uniformly at a mass ratio of 1:0.5 to obtain a mixed solvent, and then PVDF-TrEE is dissolved in the mixed solvent at a mass ratio of 1:10 to obtain a piezoelectric layer solution;

[0079] (2) Preparation of multifunctional layer solution:

[0080] S1. Preparation of photosensitizing dye solution: Add photosensitizing dye N719 to ethanol at a mass ratio of 1:1450, and stir at 30°C for 30 hours to obtain a photosensitizing dye solution;

[0081] S2. Preparation of TiO2 slurry: PEG-20000 was added to deionized water at a mass ratio of 1:7.54, and the mixture was stirred to dissolve to obtain a PEG-20000 solution. TiO2 powder, acetylacetone, and ethanol were then added to the PEG-20000 solution and alternately mixed to obtain a TiO2 dispersion. Finally, the TiO2 dispersion was uniformly mixed with a Triton X100 solution at a mass ratio of 1:0.1, and ball milled for 120 minutes to obtain a TiO2 slurry.

[0082] The mass ratio of TiO2 powder, acetylacetone, ethanol, and PEG-20000 solution is 1:0.37:0.5:7.63 by weight; the average particle size of the TiO2 powder is 25 nm; the alternating mixing refers to first magnetic stirring for 15 minutes, then ultrasonic stirring for 30 minutes, and this as one cycle, and 10 cycles are performed; the Triton X100 solution is obtained by dissolving TritonX100 in water at a volume ratio of 1:15.

[0083] S3. Preparation of a multifunctional layer solution: Spin-coat a TiO2 slurry onto glass and obtain a TiO2 porous membrane after a series of heat treatments. Then, immerse the TiO2 porous membrane in a photosensitizing dye solution and allow it to stand in the dark for 30 hours. After the solution is complete, remove the membrane, wash it, dry it, and separate it from the glass to obtain TiO2@photosensitive dye molecular powder. Finally, add the TiO2@photosensitive dye molecular powder to ethanol at a mass ratio of 1:1892 and mix them evenly to obtain a multifunctional layer solution.

[0084] The stepwise heat treatment is performed by first keeping the temperature at 50°C for 60 minutes, then keeping the temperature at 110°C for 15 minutes, and finally keeping the temperature at 500°C for 40 minutes.

[0085] (3) Preparation of composite films:

[0086] The piezoelectric layer solution is spin-coated on the conductive surface of the ITO-PEN electrode to form a piezoelectric layer after drying. Then, the multifunctional layer solution is spin-coated on the surface of the piezoelectric layer to form a multifunctional layer after drying. Finally, the piezoelectric layer solution is spin-coated on the surface of the multifunctional layer and heat-treated to form a piezoelectric layer, thereby obtaining a composite film with piezoelectric-photoelectric function on the surface of the ITO-PEN electrode; the thickness of the piezoelectric layer is 18 μm, and the thickness of the multifunctional layer is 1.1 μm.

[0087] The spin coating was performed at a speed of 2000 rpm for 90 seconds. The drying step was performed at 60° C. for 20 minutes. The heat treatment step was performed at 30° C. for 30 minutes and then at 130° C. for 0.5 hours.

[0088] (4) Preparation of sensor:

[0089] The ITO-PEN electrode of the above-mentioned composite film with piezoelectric-photoelectric function is placed face up, and then another blank ITO-PEN electrode is taken with the conductive surface facing down, and the upper surface is staggered and covered. The uncovered parts of the two electrodes are used as leads, and silicone is coated around them for fixation. The wires are fixed to the two electrode leads with conductive silver paste to obtain the multifunctional flexible piezoelectric sensor.

[0090] The output voltage of the multifunctional flexible piezoelectric sensor prepared in the embodiment of the present invention is 2.37V, and the linear relationship R2 >0.982, sensitivity is 249mV / N.

[0091] Comparative Example 1

[0092] The method is basically the same as Example 1, except that the flexible piezoelectric sensor does not have a multifunctional layer and consists of only two piezoelectric layers. The specific preparation method is as follows:

[0093] (1) Preparation of piezoelectric layer solution:

[0094] N,N-dimethylformamide and acetone were mixed uniformly at a mass ratio of 1:0.55 to obtain a mixed solvent, and then PVDF-HFP was dissolved in the mixed solvent at a mass ratio of 1:6.32 to obtain a piezoelectric layer solution;

[0095] (2) Preparation of composite films:

[0096] Spin-coating a piezoelectric layer solution on the conductive surface of an ITO-PEN electrode, drying the piezoelectric layer, and then spin-coating the piezoelectric layer solution again on the surface of the piezoelectric layer, and heat-treating the piezoelectric layer to form a piezoelectric layer, thereby obtaining a composite film with piezoelectric function on the surface of the ITO-PEN electrode;

[0097] The spin coating was performed at a speed of 1000 rpm for 60 seconds. The drying step was performed at 60° C. for 10 minutes. The heat treatment step was performed at 30° C. for 30 minutes and then at 120° C. for 1 hour.

[0098] (3) Preparation of sensor:

[0099] Place the ITO-PEN electrode surface of the above-mentioned composite film with piezoelectric function upwards, then take another blank ITO-PEN electrode and place the conductive surface downwards, staggeredly cover its upper surface, and use the uncovered parts of the two electrodes as leads. Apply silicone around them for fixation, and fix the wires at the two electrode leads with conductive silver paste to obtain the flexible piezoelectric sensor.

[0100] Figure 1 Schematic diagram of the structure of the multifunctional flexible piezoelectric sensor in Example 1.

[0101] Figure 2 This is an SEM image of the intermediate product prepared from the multifunctional layer solution in Example 1 - the TiO2 porous membrane. From this morphology image, it can be seen that the TiO2 nanoparticles with a size of about 25 nm are in the form of single particles and form a cross-linked porous membrane well, which provides a guarantee for the subsequent monolayer adsorption of photosensitizing dye molecules.

[0102] Figure 3This is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 under a periodic constant force. It can be seen from the figure that the real-time output voltage of the sensor under a periodic constant force (4.63N) has the characteristics of complete periodicity and self-powered operation. It can also be seen that under a periodic constant force of 4.63N, the output voltage of the sensor can reach 2.76V.

[0103] Figure 4 The real-time output voltage-force curve of the multifunctional flexible piezoelectric sensor in Example 1 is shown in the figure. It can be seen from the figure that there is a good linear relationship between the real-time output voltage of the sensor and the applied force (R 2 >0.967), the sensitivity of the sensor is 252mV / N.

[0104] Figure 5 This is the real-time output current-force curve of the multifunctional flexible piezoelectric sensor in Example 1. It can be seen that the current of the sensor is higher than that in the dark field when the same action is applied under light, indicating that in addition to the tactile perception and mechanical energy capture capabilities, the sensor also has light perception and light capture capabilities.

[0105] Figure 6 This is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 under continuous bending and torsion working state, which shows that the sensor can not only sense subtle changes in its own bending and torsion, but also has excellent flexibility.

[0106] Figure 7 This is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 when it is placed on the ground and stepped on by the foot. It can be seen that as the stepping force changes, the voltage also changes accordingly, indicating that the sensor can sense the changing differences in the ground force and can be integrated with the floor as an energy conversion device to collect the mechanical energy generated by human movement.

[0107] Figure 8 This is the real-time output voltage-time curve of the multifunctional flexible piezoelectric sensor in Example 1 under simulated continuous wind blowing, which shows that the sensor can sense the changes in wind blowing and can be used as an energy conversion device to capture wind energy in nature.

[0108] Figure 9 This is the real-time output voltage-time curve of the flexible piezoelectric sensor in Example 1 under a periodic constant force. It can be seen from the figure that under a periodic constant force (4.63N), the output voltage of the sensor is 1.36V, which is much lower than the output voltage of the multifunctional flexible piezoelectric sensor prepared in Example 1.

[0109] Figure 10This is the real-time output voltage-force curve of the flexible piezoelectric sensor in Example 1 under periodic constant force. It can be seen from the figure that the sensitivity of the sensor is 139mV / N.

[0110] As can be seen above, the output voltage and sensitivity of the sensor prepared in Comparative Example 1 were 1.36 V and 139 mV / N, respectively, significantly lower than those of the sensor prepared in Example 1 under the same conditions. This demonstrates that the TiO2@photosensitive dye molecular layer exhibits significant photoelectric effect, piezoelectric phase induction effect, and interface bridging effect in the sensor. Specifically, the introduction of the TiO2@photosensitive dye molecular heterojunction structure enhances piezoelectric phase formation and interface bonding within the polyvinylidene fluoride piezoelectric layer, while also creating a built-in electric field within the sensor, thereby improving the sensor's sensitivity and output voltage.

Claims

1. A method for preparing a composite film with piezoelectric-photoelectric function, characterized in that: The following steps are involved: (1) Preparation of piezoelectric layer solution: Dissolving polyvinylidene fluoride or polyvinylidene fluoride copolymer in an organic solvent at a mass ratio of 1:(5-10) to obtain a piezoelectric layer solution; (2) Preparation of multifunctional layer solution: S1. Preparation of photosensitizing dye solution: Add photosensitizing dye to ethanol at a mass ratio of 1:(1000-2000), and stir at 30-50°C for 18-30 hours to obtain a photosensitizing dye solution; S2. Preparation of TiO2 slurry: Add PEG-20000 to water at a mass ratio of 1:(5-10), stir and dissolve to obtain a PEG-20000 solution; then add TiO2 powder, acetylacetone, and ethanol to the PEG-20000 solution and alternately mix to obtain a TiO2 dispersion; finally, uniformly mix the TiO2 dispersion with Triton X100 solution at a mass ratio of 1:(0.05-0.1), and ball mill for 60-120 minutes to obtain a TiO2 slurry; The mass ratio of TiO2 powder, acetylacetone, ethanol, and PEG-20000 solution is 1: (0.2~0.5): (0.2~0.5): (4~8); S3. Preparation of a multifunctional layer solution: TiO2 slurry is coated on glass and subjected to a series of heat treatments to obtain a TiO2 porous membrane. The TiO2 porous membrane is then immersed in a photosensitizing dye solution and allowed to stand in the dark for 18 to 30 hours. After the solution is removed, washed, dried, and separated from the glass to obtain TiO2@photosensitive dye molecular powder. Finally, the TiO2@photosensitive dye molecular powder is added to ethanol at a mass ratio of 1:(1000-2000) and mixed uniformly to obtain a multifunctional layer solution. (3) Preparation of composite films: The piezoelectric layer solution is coated on the conductive surface of the ITO-PEN electrode and dried to form a piezoelectric layer. The multifunctional layer solution is then coated on the surface of the piezoelectric layer and dried to form a multifunctional layer. Finally, the piezoelectric layer solution is coated on the surface of the multifunctional layer and heat treated to form a piezoelectric layer, thereby obtaining a composite film with piezoelectric-photoelectric functions on the surface of the ITO-PEN electrode.

2. The method for preparing a composite film having piezoelectric-photoelectric functions according to claim 1, characterized in that: In step (1), the organic solvent is one or more of N,N-dimethylformamide, acetone, ethanol, cyclohexane, ethyl acetate, and chloroform.

3. The method for preparing a composite film having piezoelectric-photoelectric functions according to claim 1, characterized in that: In S1 of step (2), the photosensitizing dye is any one of N719 dye, N3 dye, coumarin, porphyrin, polymethine, carotenoid, perylene, anthocyanin, hemicyanine, pterostilbene, and chlorophyll.

4. The method for preparing a composite film having piezoelectric-photoelectric functions according to claim 1, characterized in that: In step (2) S2, the alternating mixing refers to first magnetic stirring for 15 to 30 minutes, then ultrasonic stirring for 15 to 30 minutes, which constitutes one cycle, and 6 to 10 cycles are performed.

5. The method for preparing a composite film having piezoelectric-photoelectric functions according to claim 1, characterized in that: In step (2) S3, the stepwise heat treatment refers to first keeping the temperature at 50-60°C for 30-60 min, then keeping the temperature at 100-120°C for 5-15 min, and finally keeping the temperature at 400-500°C for 20-40 min.

6. The method for preparing a composite film having piezoelectric-photoelectric functions according to claim 1, characterized in that: In step (3), the drying is carried out by keeping the temperature at 30-60°C for 5-20 minutes; the heat treatment is carried out by keeping the temperature at 30-60°C for 20-40 minutes and then keeping the temperature at 100-130°C for 0.5-2 hours.

7. The method for preparing a composite film having piezoelectric-photoelectric functions according to claim 1, characterized in that: The coating is performed by any one of spin coating, doctor blade coating, screen printing or casting.

8. A composite film with piezoelectric-photoelectric function prepared by the preparation method according to claim 1, characterized in that: The composite film comprises two piezoelectric layers and a multifunctional layer located between the two piezoelectric layers. The piezoelectric layers are polyvinylidene fluoride or polyvinylidene fluoride copolymers. The multifunctional layer is a TiO2@photosensitive dye molecule nanoheterojunction.

9. The composite film with piezoelectric-photoelectric function according to claim 8, characterized in that: The thickness of the piezoelectric layer is 10-100 μm, and the thickness of the multifunctional layer is 0.1-5 μm.

10. Use of the composite film with piezoelectric-photoelectric function as claimed in claim 8 in a multifunctional flexible piezoelectric sensor.

Images