Composite film based on organic charge transfer eutectic and preparation method and application thereof

Abstract

The invention discloses a composite film based on organic charge transfer eutectic and a preparation method and application thereof.The composite film comprises a polymer matrix and the organic charge transfer eutectic dispersed in the polymer matrix, and the polymer is selected from one or more of polyvinylidene fluoride and copolymers thereof. The organic charge transfer eutectic comprises an electron donor molecule and an electron acceptor molecule, the electron donor molecule is a polycyclic or heterocyclic aromatic molecule or benzidine molecule with a pi conjugated structure, and the electron acceptor molecule is an organic conjugated small molecule with a quinone structure or an aromatic molecule containing a cyano group. The eutectic composite film based on organic charge transfer has excellent flexibility and dielectric property, and a flexible self-functional device prepared by using the eutectic composite film as a sensing layer has high output voltage and high stable sensitive response, and can be used in the fields of low-quality energy collection and wearable sensors.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic devices, specifically to a composite thin film based on organic charge transfer eutectic, its preparation method, and its application. Background Technology

[0002] The rapid development of wearable electronic devices has created an urgent need for flexible and sustainable energy supply technologies. Traditional batteries suffer from problems such as rigidity, large size, and the need for frequent charging, making it difficult to meet the highly integrated and flexible development requirements of future wearable devices. Nanogenerators, as a self-powered technology that can harvest mechanical energy from the environment or human activities and convert it into electrical energy, offer a promising solution to this problem (Adv. Mater. 2024, 2401264). However, existing devices mostly use rigid structures or electrodes, which are prone to mechanical fatigue under repeated deformation, limiting their practical application in the wearable field (Energy Environ. Sci. 2025, 18, 4717).

[0003] Polyvinylidene fluoride (PVDF) and its copolymers (such as PVDF-hexafluoropropylene copolymer) are ideal materials for flexible nanogenerators due to their excellent flexibility, biocompatibility, and processability, and are widely used in the construction of flexible nanogenerators (Nano Energy 2022, 98, 107343). However, the output performance of PVDF nanogenerators is strongly dependent on the content of its piezoelectric active β phase and the dielectric properties of the material. The low β phase ratio (<50%) and finite dielectric constant (εr≈8-12) of pure PVDF severely limit its charge separation ability and energy conversion efficiency (Nano Energy 2023, 109). Inorganic functional fillers (such as barium titanate, perovskite, etc.) are often introduced to improve performance. However, the rigidity of inorganic phases can easily lead to a decrease in film flexibility and interfacial bonding problems, resulting in poor stability of the constructed devices. In addition, the charge transfer efficiency of such films is limited, which severely restricts the further improvement of the output voltage (typically 20-60V at ~100kPa) and sensitivity (typically 0.1-0.5V / N) of such composite materials. Furthermore, the biotoxicity of some lead-containing materials also limits their application in the wearable field (Adv. Mater. 2022, 34, e2200042).

[0004] Therefore, there is an urgent need for a composite thin film that combines flexibility, high output voltage, high sensitivity, and stability to construct high-performance self-powered electronic devices for use in low-quality energy harvesting and wearable sensor applications. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a composite thin film based on organic charge transfer eutectic, its preparation method, and its application. An organic eutectic material with high dielectric properties is constructed using a supramolecular self-assembly strategy and then composited with a flexible polymer as a filler. This achieves a synergistic improvement in the dielectric properties and mechanical flexibility of the composite thin film, resulting in a flexible self-powered electronic device with high output voltage, high sensitivity, and good stability.

[0006] Specifically, the following technical solutions are provided:

[0007] A first aspect of this invention provides a composite film based on an organic charge-transfer eutectic, comprising a polymer matrix and an organic charge-transfer eutectic dispersed in the polymer matrix; wherein,

[0008] The polymer is selected from one or more of polyvinylidene fluoride and its copolymers;

[0009] The organic charge transfer eutectic includes an electron donor molecule and an electron acceptor molecule. The electron donor molecule is a polycyclic or heterocyclic aromatic molecule or a benzidine molecule with a π-conjugated structure. The electron acceptor molecule is an organic conjugated small molecule with a quinone structure or an aromatic molecule containing a cyano group.

[0010] Furthermore, the polymer is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0011] Furthermore, the polycyclic or heterocyclic aromatic molecule is 1,3,5-tris-(4-aminobenzene)benzene, phenazine, or acridine.

[0012] Furthermore, the benzidine molecule is 4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, or 3,3',5,5'-tetramethylbenzidine.

[0013] Furthermore, the organic conjugated small molecule with a quinone structure is tetrachloro-p-benzoquinone, tetrafluoro-p-benzoquinone, 2,5-diamino-3,6-dichloro-1,4-benzoquinone, 2,5-dichloro-3,6-dihydroxy-p-benzoquinone, 2,5-dibromo-3,6-dihydroxy-p-benzoquinone, or 2,5-difluoro-3,6-dihydroxy-p-benzoquinone.

[0014] Further, the cyano-containing aromatic molecule is 1,3,5-benzotrionitrile, 1,2,4,5-tetracyanobenzene, 2,3,5,6-tetrafluoroterephthalonitrile, 4,5-difluorophthalonitrile, 3,4,5,6-tetrafluorophthalonitrile or 4,5-dichlorophthalonitrile.

[0015] Furthermore, the molar ratio of electron donor molecules to electron acceptor molecules in the organic charge transfer eutectic is preferably 1:3-3:1, such as 1:1, 1:2, 1:3, 2:1, 2:3, 3:2, 3:1, etc., including but not limited to the molar ratios listed above. If the content of electron donor molecules or electron acceptor molecules is too high, the corresponding eutectic material cannot be fully formed, and the product contains excess single crystals, which destroys the long-range order of the eutectic and the isolation of charge transport paths, thereby reducing the overall charge transfer efficiency of the composite film. Therefore, preferably, the molar ratio of the two molecules is controlled within the range of 1:3-3:1 to fully form the eutectic product.

[0016] Furthermore, the preferred mass ratio of the polymer to the organic charge-transfer eutectic is (15-20):(0.5-7).

[0017] A second aspect of this invention provides a method for preparing the composite thin film based on organic charge transfer eutectic as described in the first aspect, comprising the following steps:

[0018] The organic charge transfer eutectic or the eutectic component forming the organic charge transfer eutectic is mixed uniformly with the polymer solution to obtain a mixed solution, which is then spin-coated and dried to prepare the composite film based on the organic charge transfer eutectic.

[0019] The eutectic component includes the electron donor molecule and the electron acceptor molecule.

[0020] Further, the preparation of the organic charge transfer eutectic includes the following steps: dissolving electron donor molecules and electron acceptor molecules in a good solvent, then adding a poor solvent for liquid sealing treatment, allowing it to stand and evaporate to crystallize, thereby obtaining the organic charge transfer eutectic; preferably, the good solvent is selected from one or more of chloroform, dichloromethane, acetonitrile, tetrahydrofuran, and chlorobenzene, and the poor solvent is selected from one or more of ethanol, isopropanol, methanol, acetonitrile, cyclohexane, and n-hexane; the volume ratio of the good solvent to the poor solvent is 1:4 to 4:1.

[0021] Furthermore, the polymer solution is obtained by dissolving the polymer in a solvent, wherein the polymer is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-hexafluoropropylene copolymer, and the solvent is preferably N,N-dimethylformamide.

[0022] Further, the polymer in the polymer solution preferably accounts for 15%-20% of the total mass; the ratio of the mass of the organic charge-transfer eutectic or the total mass of the eutectic components forming the organic charge-transfer eutectic to the mass of the polymer solution is (0.5-7):100, more preferably (0.5-1):100, for example 0.75:100.

[0023] In this invention, the amount of organic charge transfer eutectic or its eutectic components added to the polymer solution should not be too much or too little. If the amount added is too little, the output voltage cannot be effectively improved; however, the amount added should not be too much either, as excessive eutectic will agglomerate during the drying process, severely hindering the orderly arrangement and regular stacking of polyvinylidene fluoride-hexafluoropropylene molecular chains during crystallization, leading to a decrease in matrix crystallinity and an increase in crystal defects. In addition, filler agglomerates can become stress concentration points and may lead to charge leakage. These factors work together to weaken the overall piezoelectric properties of the composite material, resulting in a gradual decrease in output voltage. Therefore, in order to fully utilize the synergistic effect between the organic charge transfer eutectic and polyvinylidene fluoride-hexafluoropropylene, and improve the polarization effect and charge transfer efficiency, preferably, the ratio of the mass of the organic charge transfer eutectic or the total mass of the eutectic components forming the organic charge transfer eutectic to the mass of the polymer solution is controlled at (0.5-1):100, more preferably 0.75:100.

[0024] Furthermore, the spin coating rate is preferably 300-600 r / min.

[0025] Furthermore, the drying temperature is preferably 50-90°C, and the drying time is preferably 1-10 hours.

[0026] The third aspect of this invention provides the application of the composite thin film based on organic charge transfer eutectic described in the first aspect in flexible self-powered devices.

[0027] A fourth aspect of the present invention provides a flexible self-powered device, comprising a first conductive substrate layer, a sensing layer and a second conductive substrate layer stacked sequentially, wherein the sensing layer is a composite thin film based on organic charge transfer eutectic as described in the first aspect.

[0028] Further, the first conductive substrate layer includes a first polymer substrate and a first conductive layer disposed on the outer surface of the first polymer substrate; the second conductive substrate layer includes a second polymer substrate and a second conductive layer disposed on the outer surface of the second polymer substrate; the materials of the first polymer substrate and the second polymer substrate are respectively selected from polyethylene terephthalate, polylactic acid, and thermoplastic polyurethane; the materials of the first conductive layer and the second conductive layer include, but are not limited to, silver or copper.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention provides a composite thin film based on organic charge transfer eutectic. By selecting the types of organic eutectic molecules and combining them with a supramolecular self-assembly strategy, an organic eutectic material with high dielectric properties is constructed. This material is then used as a filler to composite with a flexible polymer, thereby achieving a synergistic improvement in the dielectric properties and mechanical flexibility of the composite thin film. This results in a flexible self-powered electronic device with high output voltage, high sensitivity, and good stability, opening up new avenues for the development of efficient and flexible self-powered devices.

[0031] 2. This invention also provides a method for preparing the above-mentioned composite thin film based on organic charge transfer eutectic. The method involves dissolving an organic charge transfer eutectic with an asymmetric central structure, or electron donor and acceptor molecules capable of forming the above-mentioned organic charge transfer eutectic, in a specific polymer solution. A wet film is then formed by spin-coating. During the drying process of the wet film, the electron donor and acceptor molecules self-assemble in situ to form a eutectic structure, resulting in a composite thin film embedded with the organic charge transfer eutectic. The above preparation method is simple, the conditions are easily controlled, and the raw materials are inexpensive and readily available, making it suitable for mass production.

[0032] 3. This invention also provides a flexible self-powered device, using the aforementioned composite thin film based on organic charge transfer eutectic as the sensing layer. This flexible self-powered device not only possesses excellent flexibility and resilience, but also exhibits high sensitivity to force, fast response speed, high output voltage (output voltage not less than 90V under 50N pressure), and short recovery time. It demonstrates a stable output signal in 1000 pressure tests, showing good repeatability and stability, and has promising application prospects in low-quality energy harvesting and wearable sensor fields. Attached Figure Description

[0033] Figure 1 This invention relates to electron donor molecular structures of polycyclic or heterocyclic aromatic molecules or benzidine molecules having π-conjugated structures.

[0034] Figure 2 These are electron acceptor molecular structures that have a quinone structure or contain a cyano group, as described in this invention.

[0035] Figure 3 The X-ray diffraction patterns of the organic eutectic material and the single-molecule crystal material prepared in Example 1 are shown below.

[0036] Figure 4 The graph shows the dielectric properties of the organic eutectic material prepared in Example 1.

[0037] Figure 5 a is a schematic diagram of the self-powered device; b is a bent image of the self-powered device; c is a folded image of the self-powered device; d is a restored image of the self-powered device after folding.

[0038] Figure 6 A comparison diagram of the output voltage of the pure polymer film prepared in Example 1 and the self-powered device constructed based on the composite film of organic eutectic material, single electron acceptor molecular crystal, and single electron donor molecular crystal.

[0039] Figure 7 The output performance diagrams of the self-powered device constructed from a composite thin film based on organic eutectic material prepared in Example 1 are as follows: a is the pressure-voltage diagram, b is the response time and recovery time diagram, and c is the output voltage diagram after 1000 cycles.

[0040] Figure 8 The output voltage comparison diagram shows the self-powered device prepared using pure polyvinylidene fluoride-hexafluoropropylene as the sensing layer in Example 1 and the self-powered devices prepared in Examples 1-6.

[0041] Figure 9 Comparison of the output voltages of the self-powered devices prepared in Examples 7 and 8;

[0042] Figure 10 This is a schematic diagram of the fabrication process and application of the self-powered device in this invention;

[0043] Figure 11 The following are application effect diagrams of the self-powered device in this invention: a) Lighting up an LED by applying pressure to the self-powered device; b) Output signal when the self-powered device is attached to a finger and the finger is bent at different angles; c) Output signal when the self-powered device is attached to the wrist and the wrist is bent at 45°; d) Output signal when the self-powered device is attached to the elbow and the elbow is bent at 90°. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0046] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0047] Example 1

[0048] This embodiment relates to the fabrication of a composite thin film and a self-powered device based on organic charge transfer eutectic, and the specific operations are as follows:

[0049] (1) Add 0.035 g of 1,3,5-tris-(4-aminobenzene)benzene and 0.036 g of 1,2,4,5-tetracyanobenzene to 15 mL of dichloromethane and sonicate for 10 min to obtain an electron donor-acceptor organic solvent stock solution; take 3 mL of ethanol solution and slowly drip it into the stock solution along the bottle wall, let it stand for several days until the solvent completely evaporates to obtain an organic eutectic material.

[0050] 2.25g of polyvinylidene fluoride-hexafluoropropylene particles were added to 10.25g of N,N-dimethylformamide and stirred for 10h to obtain a polyvinylidene fluoride-hexafluoropropylene solution; 0.0075g of organic eutectic material was weighed and added to 1g of polyvinylidene fluoride-hexafluoropropylene solution and stirred for 30min to obtain a polyvinylidene fluoride-hexafluoropropylene solution with a eutectic content of 0.75%.

[0051] (2) Using spin coating, two polyethylene terephthalate (PET) films measuring 2cm × 3cm were taken and coated with silver paste as electrodes at a spin speed of 2000 r / min. The films were then dried in an oven at 60°C for 1 hour. After drying, a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFA) solution with a eutectic content of 0.75% was spin-coated onto one of the PET films at a spin speed of 500 r / min for 1 minute. After spin coating, the films were dried in a vacuum drying oven at 90°C for 10 hours to form a sensing layer. The two dried PET films were then removed, and the sensing layer of the PET film with the piezoelectric layer was placed facing inwards and bonded to the other PET film to obtain a self-powered device.

[0052] Depend on Figure 3 It can be seen that the organic eutectic material prepared in this embodiment exhibits characteristic diffraction peaks that are significantly different from those of 1,3,5-tris-(4-aminobenzene)benzene crystals and 1,2,4,5-tetracyanobenzene crystals, indicating the formation of organic eutectic.

[0053] The dielectric properties of the organic eutectic material prepared in this embodiment were tested, and the test results are as follows: Figure 4 As shown, the dielectric constant of the organic eutectic material can reach as high as 10.21, and it has low dielectric loss. This also indicates that the 1,3,5-tris-(4-aminobenzene)benzene-1,2,4,5-tetracyanobenzene eutectic material with high dielectric constant has been successfully prepared.

[0054] A schematic diagram of the self-powered device prepared in this embodiment is shown below. Figure 5 As shown in a, by Figure 5As shown in b-5d, the device has good flexibility and resilience, and can reversibly bend and fold at any angle.

[0055] To further investigate the influence of eutectic materials on the output performance of self-powered devices, this embodiment uses pure polyvinylidene fluoride-hexafluoropropylene (PVDF-HFA) as the sensing layer to prepare self-powered devices. Furthermore, it prepares corresponding PVDF-HFA self-powered devices based on 1,3,5-tris-(4-aminobenzene)benzene and PVDF-HFA self-powered devices based on 1,2,4,5-tetracyanobenzene by replacing the organic eutectic material. Under the same pressure (50 N), the output voltage of different self-powered devices was tested, such as... Figure 6 As shown, compared to the self-powered devices prepared using pure polyvinylidene fluoride-hexafluoropropylene as the sensing layer, the output voltage of the self-powered devices prepared by introducing 1,3,5-tris-(4-aminobenzene)benzene crystals did not change significantly. Although the output voltage of the self-powered devices prepared by introducing 1,2,4,5-tetracyanobenzene crystals increased, the increase was limited, and the output voltage was still below 50V. However, the output voltage of the self-powered devices prepared by the organic eutectic material formed by the electron donor molecules and electron acceptor molecules was significantly improved (~90V). This also shows that the addition of eutectic can effectively improve the output performance of the self-powered devices.

[0056] Furthermore, the output performance, sensitivity, and stability of the self-powered device based on organic charge transfer eutectic prepared in this embodiment under different pressures were further tested, such as... Figure 7 As shown in Figure a, the output voltage of the self-powered device increases with increasing pressure, and it has a fast response speed, requiring only 105.9 ms to respond and recovering within 84.3 ms. Figure 7 b). Apply the same pressure to the self-powered device and release it, repeating this operation 1000 times, with the following results: Figure 7 As shown in Figure c, the output signal remained stable during 1000 pressurization tests, demonstrating good repeatability and stability.

[0057] Example 2

[0058] This embodiment relates to the preparation of a composite thin film based on organic charge transfer eutectic and a self-powered device. The only difference from Example 1 is that the eutectic content in step (1) is 0.5%; the rest of the operations are the same, and the corresponding self-powered device is prepared.

[0059] like Figure 8As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 80V under a constant pressure of 50N.

[0060] Example 3

[0061] This embodiment relates to the preparation of a composite thin film based on organic charge transfer eutectic and a self-powered device. The only difference from Embodiment 1 is that the eutectic content in step (1) is 1%; the rest of the operations are the same, and the corresponding self-powered device is prepared.

[0062] like Figure 8 As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 85V under a constant pressure of 50N.

[0063] Example 4

[0064] This embodiment relates to the preparation of a composite thin film based on organic charge transfer eutectic and a self-powered device. The only difference from Embodiment 1 is that the eutectic content in step (1) is 3%; the rest of the operations are the same, and the corresponding self-powered device is prepared.

[0065] like Figure 8 As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 65V under a constant pressure of 50N.

[0066] Example 5

[0067] This embodiment relates to the preparation of a composite thin film based on organic charge transfer eutectic and a self-powered device. The only difference from Embodiment 1 is that the eutectic content in step (1) is 5%; the rest of the operations are the same, and the corresponding self-powered device is prepared.

[0068] like Figure 8 As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 60V under a constant pressure of 50N.

[0069] Example 6

[0070] This embodiment relates to the preparation of a composite thin film based on organic charge transfer eutectic and a self-powered device. The only difference from Embodiment 1 is that the eutectic content in step (1) is 7%; the rest of the operations are the same, and the corresponding self-powered device is prepared.

[0071] like Figure 8 As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 23V under a constant pressure of 50N.

[0072] Example 7

[0073] This embodiment relates to the preparation of a composite thin film and a self-powered device based on organic charge transfer eutectic. The only difference from Embodiment 1 is that the preparation of the polyvinylidene fluoride-hexafluoropropylene solution in step (1) is as follows: 0.0037g of phenazine and 0.0063g of 2,5-dichloro-3,6-dihydroxy-p-benzoquinone are weighed and added to 1g of polyvinylidene fluoride-hexafluoropropylene solution and stirred for 30min to obtain a polyvinylidene fluoride-hexafluoropropylene solution with a eutectic content of 0.75%, which is then set aside.

[0074] All other operations were performed in the same manner, and the corresponding self-powered device was successfully prepared.

[0075] like Figure 9 As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 90N under a constant pressure of 50N.

[0076] Example 8

[0077] This embodiment relates to the preparation of a composite thin film and a self-powered device based on an organic charge transfer eutectic. The only difference from Example 1 is the preparation of the polyvinylidene fluoride-hexafluoropropylene solution in step (1). Specifically, 0.0046 g of phenazine and 0.0054 g of 2,5-dichloro-3,6-dihydroxy-p-benzoquinone are weighed and added to 1 g of polyvinylidene fluoride-hexafluoropropylene solution and stirred for 30 min to obtain a polyvinylidene fluoride-hexafluoropropylene solution with a eutectic content of 1%, which is then set aside. All other operations are the same, and the corresponding self-powered device is prepared.

[0078] like Figure 9 As shown, the self-powered device based on organic charge transfer eutectic prepared in this embodiment has an output voltage of 35N under a constant pressure of 50N.

[0079] application

[0080] Taking the self-powered device prepared in Example 1 as an example, the self-powered device is used to self-power a light bulb and to monitor signals of daily human activities, as detailed below:

[0081] like Figure 11 As shown in Figure a, when mechanical pressure is applied to a self-powered device, the electrical energy generated by the device is converted from AC to DC by a bridge rectifier, and its output voltage is sufficient to light up 100 light bulbs at once.

[0082] Furthermore, integrating this self-powered device into smart clothing or wearable devices can be used for real-time monitoring of daily activities and physiological signals. For example... Figure 11 As shown in b-11d, after the device is attached to different parts of the human body, it can detect various physiological movements such as finger, wrist, and elbow flexion in real time. As the finger continuously flexes from 0° to 90°, the electrical signal increases accordingly. Figure 11b) Similarly, by fixing the device to the wrist and elbow, the movement of large joints can also be accurately monitored.

[0083] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite thin film based on organic charge transfer eutectic, characterized in that, It includes a polymer matrix and an organic charge-transfer eutectic dispersed in the polymer matrix; wherein, The polymer is selected from one or more of polyvinylidene fluoride and its copolymers; The organic charge transfer eutectic includes an electron donor molecule and an electron acceptor molecule. The electron donor molecule is a polycyclic or heterocyclic aromatic molecule or a benzidine molecule with a π-conjugated structure. The electron acceptor molecule is an organic conjugated small molecule with a quinone structure or an aromatic molecule containing a cyano group.

2. The composite film according to claim 1, characterized in that, The polymer is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-hexafluoropropylene copolymer; The polycyclic or heterocyclic aromatic molecule is 1,3,5-tris-(4-aminobenzene)benzene, phenazine, or acridine; The benzidine molecule is 4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, or 3,3',5,5'-tetramethylbenzidine; The organic conjugated small molecules with quinone structures are tetrachloro-p-benzoquinone, tetrafluoro-p-benzoquinone, 2,5-diamino-3,6-dichloro-1,4-benzoquinone, 2,5-dichloro-3,6-dihydroxy-p-benzoquinone, 2,5-dibromo-3,6-dihydroxy-p-benzoquinone, or 2,5-difluoro-3,6-dihydroxy-p-benzoquinone; The cyano-containing aromatic molecule is 1,3,5-benzotrionitrile, 1,2,4,5-tetracyanobenzene, 2,3,5,6-tetrafluoroterephthalonitrile, 4,5-difluorophthalonitrile, 3,4,5,6-tetrafluorophthalonitrile, or 4,5-dichlorophthalonitrile.

3. The composite film according to claim 1 or 2, characterized in that, The molar ratio of electron donor molecules to electron acceptor molecules in the organic charge transfer eutectic is 1:3 to 3:

1.

4. The composite film according to claim 1 or 2, characterized in that, The mass ratio of the polymer to the organic charge-transfer eutectic is (15-20):(0.5-7).

5. A method for preparing a composite thin film according to any one of claims 1-4, characterized in that, Includes the following steps: The organic charge transfer eutectic or the eutectic component forming the organic charge transfer eutectic is mixed uniformly with the polymer solution to obtain a mixed solution, which is then spin-coated and dried to prepare the composite film based on the organic charge transfer eutectic. The eutectic component includes the electron donor molecule and the electron acceptor molecule.

6. The preparation method according to claim 5, characterized in that, The polymer solution is obtained by dissolving the polymer in a solvent; The solvent is N,N-dimethylformamide; The polymer in the solution comprises 15%-20% by mass.

7. The preparation method according to claim 5, characterized in that, The spin coating rate is 300-600 r / min; The drying temperature is 50-90℃, and the time is 1-10h.

8. The application of the composite thin film based on organic charge transfer eutectic as described in any one of claims 1-4 in a flexible self-powered device.

9. A flexible self-powered device, characterized in that, It includes a first conductive substrate layer, a sensing layer and a second conductive substrate layer stacked sequentially, wherein the sensing layer is a composite thin film based on organic charge transfer eutectic as described in any one of claims 1-4.

10. The flexible self-powered device according to claim 9, characterized in that, The first conductive substrate layer includes a first polymer substrate and a first conductive layer disposed on the outer surface of the first polymer substrate; The second conductive substrate layer includes a second polymer substrate and a second conductive layer disposed on the outer surface of the second polymer substrate; The materials of the first polymer substrate and the second polymer substrate are respectively selected from polyethylene terephthalate, polylactic acid, and thermoplastic polyurethane; The materials of the first conductive layer and the second conductive layer include silver or copper.

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