High-performance self-supporting silver selenide / carbon composite flexible thermoelectric thin film, preparation and application thereof

Abstract

The application relates to a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film and preparation and application thereof, and the preparation process of the flexible thermoelectric film comprises the following steps: (1) polyvinylpyrrolidone is added into ethylene glycol, heating and stirring are carried out to obtain a mixed solvent, then silver selenide powder is stirred with the mixed solvent to obtain a precursor slurry; (2) the precursor slurry is printed on a polyimide substrate by using a silk screen printing technology and is dried to obtain a film precursor; (3) the film precursor is heated and annealed in a vacuum environment, then, cooling is carried out to room temperature, the substrate is removed by peeling to obtain a composite film, and the composite film is the target product. The application has the advantages of low cost, simple operation and scale-up, and the prepared self-supporting composite film exhibits excellent thermoelectric performance and flexibility; the flexible thermoelectric device assembled by using the film has excellent output performance and flexibility, and can be used for wearable flexible electronic equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermoelectric material preparation, and relates to a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film and preparation and application thereof. BACKGROUND

[0002] With the rapid development of the Internet of Things technology and wearable electronic devices, the demand for energy supply technology that can work continuously and matching functional materials is increasingly urgent. Flexible thermoelectric materials are a kind of green functional materials that can continuously generate electricity by utilizing the temperature difference between the human body and the environment. Flexible thermoelectric devices prepared by using flexible thermoelectric materials have the advantages of all-solid-state, lightweight, no noise, small volume and maintenance-free, and are easy to integrate into multifunctional microelectronic devices, thus having a broad application prospect in the field of energy supply. The performance of thermoelectric materials is usually evaluated by a dimensionless merit value (ZT), and the calculation formula is: ZT = α2σT / κ, wherein α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the thermodynamic temperature. α2σ is called the power factor (PF).

[0003] In recent years, research on flexible thermoelectric materials has gradually increased and certain research progress has been made in the field of flexible thermoelectric films, which can be divided into two categories: flexible substrate support and self-supporting flexible thermoelectric films. The former is usually to deposit thermoelectric materials on a flexible polymer substrate to obtain flexibility. However, the flexible substrate will affect the effective collection of heat and the accurate testing of thermal characteristics, and the flexible substrate will generate additional stress during bending, thereby limiting the flexibility of the composite film. In addition, techniques such as magnetron sputtering, thermal evaporation, vacuum-assisted filtration and hot pressing are adopted and high-performance thermoelectric films supported by flexible substrates are obtained. However, these techniques are high in cost, high in energy consumption, difficult to operate and cannot be scaled up.

[0004] Self-supporting flexible thermoelectric films are mainly divided into conductive polymer-based materials, carbon-based materials and plastic inorganic films. The first two are usually to use conductive polymers (such as PEDOT:PSS, etc.) and carbon materials (such as carbon nanotubes, etc.) with excellent mechanical properties as flexible substrates, and then use inorganic thermoelectric materials as fillers to synergistically optimize the thermoelectric performance and flexibility of the composite film by adjusting the proportion of the two phases. However, the intrinsic thermoelectric performance and thermal stability of conductive polymers are poor, the Seebeck coefficient of carbon materials is low, the thermal conductivity is high, and a large number of heterogeneous interfaces formed after compounding easily strongly scatter carriers, resulting in that the thermoelectric performance of the composite material is still far lower than that of bulk thermoelectric materials. Plastic inorganic films based on silver sulfide-based materials exhibit excellent ductility, but their thermoelectric performance is generally low, which cannot meet the energy supply demand of electronic devices, and their preparation cycle is long and the conditions are harsh, which is not conducive to their commercial application in the field of flexible electronics.

[0005] Silver selenide is a kind of narrow band gap n-type semiconductor, silver selenide has a positive structure at low temperature, showing semiconductor characteristics, and its crystal structure will change at about 407K, transforming into a cubic structure, showing superionic conductor characteristics, so the current research mainly focuses on the near room temperature performance of silver selenide-based thermoelectric materials. The bulk silver selenide of the orthorhombic phase has high electrical conductivity, high mobility and low thermal conductivity, and has excellent near room temperature thermoelectric performance. However, there are few studies on self-supporting silver selenide-based flexible thermoelectric films at present, and the reported thermoelectric performance is low, the preparation cost is high, the time is long, the technology is complex, and the product size is limited, which limits its further application in flexible thermoelectric materials.

[0006] As provided in Chinese patent CN202010607248.X, a method for preparing a high-performance polyvinylpyrrolidone / silver selenide / nylon flexible composite thermoelectric film, comprising the following steps: (1) using selenium nanowire as a template, reacting with silver nitrate in ethylene glycol solvent, and adding polyvinylpyrrolidone during the reaction to obtain polyvinylpyrrolidone-coated silver selenide multi-scale nanostructure; (2) dispersing the polyvinylpyrrolidone-coated silver selenide multi-scale nanostructure in anhydrous ethanol, using a nylon filter membrane as a substrate, and performing suction filtration, vacuum drying and hot pressing to obtain the target product polyvinylpyrrolidone / silver selenide / nylon composite film. The silver selenide nanostructure synthesized by the patent is greatly affected by environmental conditions, and the polyvinylpyrrolidone added during the synthesis process does not carbonize after hot pressing and still maintains insulating properties, which is not conducive to improving electrical performance; at the same time, the prepared flexible film is tightly combined with the nylon substrate, which not only affects the accurate measurement of thermoelectric performance, but also limits its mechanical flexibility; in addition, the preparation of the film requires expensive hot pressing equipment, which is high in cost and is not conducive to large-scale application. SUMMARY

[0007] The purpose of the present application is to provide a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film and its preparation and application. The prepared self-supporting composite film exhibits excellent thermoelectric performance and flexibility.

[0008] The purpose of the present application can be achieved by the following technical solutions:

[0009] In one aspect, the present application provides a method for preparing a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film, comprising the following steps:

[0010] (1) adding polyvinylpyrrolidone to ethylene glycol, heating and stirring to obtain a mixed solvent, and then stirring silver selenide powder with the mixed solvent to obtain a precursor slurry;

[0011] (2) printing the precursor slurry on a polyimide substrate using a screen printing technique and drying to obtain a film precursor;

[0012] (3) heating and annealing the thin film precursor in a vacuum environment, then cooling to room temperature, removing the substrate by peeling to obtain a composite thin film, which is the target product.

[0013] Further, the polyvinylpyrrolidone and ethylene glycol are added in a ratio of (1.5-2.5) g: 10 mL, preferably 2 g: 100 mL.

[0014] Further, in step (1), the temperature of heating and stirring is 60-80℃, preferably 70℃.

[0015] Further, in step (1), the mass ratio of silver selenide powder to mixed solvent is 6-10:1.

[0016] Further, in step (1), the stirring time of silver selenide powder and mixed solvent is 16-32 h, preferably 24 h.

[0017] Further, in step (2), the mesh size of the screen plate used in the screen printing technique is 250 mesh.

[0018] Further, in step (3), the heating and annealing is performed in a tube furnace.

[0019] Further, in step (3), the heating and annealing temperature is 400-450℃, preferably 420-450℃, more preferably 450℃, and the time is 2-3 h.

[0020] Further, in the heating and annealing process, the temperature rising rate is 2.5-5℃ / min.

[0021] Further, in step (3), the substrate is removed by peeling, and the edge region with a width of 0.5-1.5 mm (preferably about 1 mm) is cut off.

[0022] Further, the silver selenide is prepared by one-pot method.

[0023] In a second aspect, the present application provides a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film, which is prepared by the preparation method as described above.

[0024] In a third aspect, the present application provides the use of a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film in a flexible thermoelectric device or a portable wearable electronic device.

[0025] The formation mechanism of the self-supporting silver selenide / carbon composite flexible thermoelectric film is speculated as follows:

[0026] First, polyvinylpyrrolidone was chosen as the binder, mixed with low-boiling ethylene glycol to obtain a solvent with good fluidity and viscosity, which was mixed with silver selenide powder in a certain proportion to obtain an ink with good stability. Then, a simple and scalable screen printing technology was used to print the ink onto a polyimide substrate with high thermal stability (its thickness was selected as 150 μm to ensure that it would not be deformed by heat). Then, the printed film was annealed in a vacuum furnace. During the annealing process, the low-boiling ethylene glycol in the film evaporated, and at the same time, the polyvinylpyrrolidone in the solvent carbonized, resulting in a carbon content gradient along the out-of-plane direction. The evaporation of the solvent left a small amount of micropores in the film, which helped the film release stress and consume energy during bending. In addition, when the viscous solvent near the smooth polyimide substrate surface evaporated, the binding force between the remaining silver selenide / carbon composite film and the polyimide substrate decreased significantly, which made the silver selenide / carbon composite film easy to peel off from the polyimide substrate to become a self-supporting film. At the same time, in the initial annealing stage, the escape of the solvent left space for the silver selenide grains to settle, and the silver selenide grains grew further with the assistance of the residual fluidity of the solvent, showing good crystallinity. The residual polyvinylpyrrolidone was eventually pyrolyzed into carbon with low thermal conductivity and attached to the silver selenide grain boundaries. Due to the double blocking of the dense and smooth polyimide substrate and the settled upper silver selenide layer, the silver selenide grains near the bottom of the film tended to grow in the in-plane direction. In contrast, the silver selenide grains on the surface of the film tended to grow freely into equiaxed crystals due to exposure to vacuum. Therefore, the silver selenide grains formed a textured gradient from the bottom to the surface of the film, which was beneficial to the high flexibility of the composite film. The prepared self-supporting silver selenide / carbon composite film has excellent flexibility and excellent thermoelectric performance.

[0027] The present application utilizes a one-pot method to synthesize silver selenide powder, which is then mixed with polyvinylpyrrolidone and ethylene glycol in a certain proportion to obtain a thermoelectric ink with good fluidity, and then a scalable screen printing technology is used to print a film, and through a simple annealing process and a simple substrate peeling process, a self-supporting silver selenide / carbon flexible composite film with high thermoelectric performance and excellent flexibility is prepared. Specifically, the silver selenide / carbon composite film structure is relatively dense, composed of well-crystallized micro-nano silver selenide grains and a small amount of carbon, showing a relatively high room temperature PF, while the film has a small number of pores, multiple size defects and heterogeneous interfaces, resulting in a relatively low κ, and its room temperature ZT value can reach 0.81. In addition, thanks to the combination of the double gradients of carbon content and silver selenide texturing level in the out-of-plane direction, the film shows excellent flexibility. The four-arm thermoelectric device assembled with the optimized film outputs a maximum power of 5.5 μW and a power density of 22.9 W m -2 at a temperature difference of 31.4 K, and exhibits good flexibility.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] (1) The preparation process is low in cost, the thermoelectric ink (i.e. precursor slurry) is simple to synthesize, the mature screen printing technology and simple thermal annealing process are adopted, the energy consumption is low, and the preparation can be scaled up;

[0030] (2) The prepared flexible composite film does not need a flexible substrate for support, so the interface problem between the thermoelectric film and the substrate is avoided, and the effective collection of heat and the direct and accurate testing of the thermoelectric performance are facilitated;

[0031] (3) In the prepared self-supporting silver selenide / carbon composite film, the nano- to sub-micron-sized silver selenide grains have good crystallinity and coherent grain boundaries, a small amount of adhesive carbon exists in the nanopores and / or grain boundaries, and in addition, there are multiple size defects, which are beneficial to the synergistic optimization of the thermoelectric transport properties;

[0032] (4) The prepared film has excellent thermoelectric performance, and the optimized room temperature ZT value (-0.81) of the film is one of the highest values in the reported self-supporting flexible thermoelectric films;

[0033] (5) The prepared film has a carbon content gradient along the out-of-plane direction and a silver selenide texturing level gradient, and the double gradients jointly construct the flexible structure of the self-supporting film, and a small amount of micropores in the film are also beneficial to the release of bending stress, so the composite film shows excellent flexibility and can withstand 3000 bending cycles at a bending radius of 4 mm while maintaining more than 90% of the electrical conductivity;

[0034] (6) The flexible thermoelectric device prepared from the film has excellent performance, can output high power density at a low temperature difference, and has good flexibility, and can be applied to heat collection and power generation of wearable electronic devices in different scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 FESEM images of the surface and back of the sample film1 prepared in Example 1.

[0036] Figure 2 FESEM images of the cross section of the sample film1 prepared in Example 1 and the corresponding EDS energy spectrum of C, Ag and Se elements.

[0037] Figure 3 XRD patterns of the surface and back of the sample film1 prepared in Example 1.

[0038] Figure 4 XPS of the surface and back of the sample film1 prepared in Example 1 within a depth range of 90nm.

[0039] Figure 5 The Raman spectra of the sample film1 prepared in Example 1 at different depths from the bottom to the surface on the cross section.

[0040] Figure 6 These are transmission electron microscopy (TEM) images of sample film1 obtained in Example 1 at different resolutions.

[0041] Figure 7 The temperature-dependent thermoelectric properties of sample film1 prepared in Example 1 and its ZT value are compared with the ZT values ​​of self-supporting flexible thermoelectric films reported in other literature.

[0042] Figure 8 The results of the flexibility test of sample film1 prepared in Example 1 are presented, and the flexibility is compared with that of flexible thermoelectric films reported in other literature.

[0043] Figure 9 The output performance of the four-arm flexible thermoelectric device assembled from sample film1 prepared in Example 1.

[0044] Figure 10 The flexibility of the four-arm flexible thermoelectric device assembled from sample film1 obtained in Example 1. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0046] In the following embodiments, the flexible polyimide substrates were all purchased from Zhongshan Chenxi Technology Co., Ltd. Unless otherwise specified, all other raw materials or processing techniques are commercially available and conventional in the art.

[0047] Example 1:

[0048] A method for preparing a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film involves the sequential and slow addition of 0.005 mol silver nitrate, 0.025 mol potassium hydroxide, 1 mL 3-mercaptopropionic acid, 0.005 mol selenium dioxide, and 0.015 mol potassium borohydride to 500 mL of deionized water. The mixture is then stirred and reacted in an oil bath at 40 °C for 5 h. Afterward, the precipitate is washed twice by alternating centrifugation with deionized water and anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 60 °C for 12 h, and finally ground to obtain silver selenide powder.

[0049] Polyvinylpyrrolidone (PVP-K30) and ethylene glycol were heated and stirred at 70°C for 30 min at a ratio of 2 g: 10 mL, and then naturally cooled to room temperature to obtain a solvent. Silver selenide powder was then mixed with the solvent at a mass ratio of 8:1 and stirred for 24 h. The mixture was then printed onto a 150 μm thick flexible polyimide substrate using a 250-mesh screen and dried in a vacuum oven at 60°C for 12 h. After drying, the sample was placed in a ceramic boat and then placed in a tube furnace, where it was annealed at 450°C for 2 h under vacuum. After the tube furnace cooled naturally to room temperature, the sample was removed, and a 1 mm wide area was trimmed from the film edge. The polyimide substrate was then peeled off to obtain a self-supporting silver selenide / carbon composite flexible thermoelectric film (film1) with a thickness of approximately 13 μm.

[0050] Figure 1 Field emission scanning electron microscopy (FESEM) images of the surface and back side of sample film1 are shown. The surface morphology of the film is relatively rough, with equiaxed grains and a small number of micropores. In contrast, the back side of the film has a relatively smooth morphology and higher density, which may be due to the growth of silver selenide grains along the c-axis on the smooth and dense polyimide substrate surface. Furthermore, as... Figure 2 As shown, the cross-sectional FESEM image of sample film1, with a thickness of approximately 13 μm, reveals weak texturing along the planar direction. In the EDS spectrum corresponding to the cross-sectional FESEM image, the C element exhibits a gradient content variation, forming a carbon-rich layer near the film surface, while Ag and Se elements are relatively uniformly distributed. The X-ray diffraction (XRD) patterns of the film surface and back side are shown below. Figure 3 As shown, the XRD pattern matches well with the standard PDF card (PDF#24-1041) of the silver selenide orthorhombic phase. Furthermore, a hump is present in the XRD pattern of the film surface, which can be attributed to the presence of amorphous carbon. Moreover, the intensity of this peak is higher than that of the XRD pattern on the back side of the film, which is related to the higher carbon content on the film surface compared to the bottom. Simultaneously, the intensity of the (00l) diffraction peaks containing the (002) and (004) planes in the XRD pattern on the back side of the film is simultaneously enhanced compared to the film surface, indicating that the (00l) texture of the silver selenide grains at the bottom of the film is higher than that at the film surface. X-ray photoelectron spectroscopy (XPS) of sample film1 in the 90 nm depth range was obtained using in-situ etching technology, and together with the XPS pattern on the back side of the film... Figure 4 The results are shown in the figure. With increasing depth, the O 1s peak intensity decreases rapidly, indicating that oxidation below the film surface is suppressed. Importantly, the Ag 3d peak position remains essentially unchanged, indicating the stable presence of stoichiometric silver selenide in the composite film. The relative intensity of the Ag 3d peak gradually increases, indicating a gradual increase in silver selenide content and a gradual decrease in carbon content from the film surface to the bottom. Raman spectroscopy measurements were performed on the cross-section of sample film1 from bottom to surface, and the results are shown in the figure. Figure 5As shown. Located at 1350 and 1580cm -1 The two nearby spikes belong to the D and G bands, which are related to carbon defects and graphitization. Another spike is at 2580 cm⁻¹. -1 The broad peaks on the left and right correspond to 2D bands, which are caused by the accumulation of trace amounts of graphitized carbon. The three characteristic peaks of carbon indicate that polyvinylpyrrolidone is carbonized during annealing. Notably, under the same laser source and intensity, the detection intensity of these characteristic peaks gradually increases from the bottom of the film to the surface, indicating that the carbon content gradually increases along the out-of-plane direction.

[0051] Figure 6 (a) shows a low-magnification transmission electron microscopy (TEM) image of a typical region of sample film1, containing dense silver selenide polycrystals and fewer nanopores. Figure 6 (b) shows Figure 6 (a) is a high-resolution TEM (HRTEM) image of the area marked by the red box, which contains several silver selenide grains surrounded by a layer of carbon with a thickness of nanometers. Figure 6 (c) is Figure 6 (b) shows a magnified image of the lattice distortion region marked with a brown square, exhibiting typical stacking fault (SF) characteristics, resulting in slight pattern overlap in the Fast Fourier Transform (FFT) modes in the upper left inset. Another inverse Fourier Transform image shows the presence of edge dislocations. These localized lattice defects enhance phonon scattering, thereby reducing κ. Figure 6 (d) shows Figure 6 (b) shows a more ordered lattice arrangement region marked with green squares, revealing three silver selenide nanocrystals with coherent grain boundaries (GBs), which facilitate electron transport while hindering phonon propagation. Furthermore, in Figure 6 (d) The presence of amorphous rings in the corresponding FFT image indicates the presence of trace amounts of amorphous carbon within the silver selenide grains. Figure 6 As shown in (e), carbon adheres to the area around GBs, not only tightly binding the silver selenide grains but also filling and healing some large cracks between the grains. This helps the silver selenide / carbon composite film withstand external stress, thus exhibiting good mechanical properties. Figure 6 (e) is a magnified image of the carbon coating area marked by the blue box. Figure 6 In (f), a small number of ordered striations appear at the edges of silver selenide grains, indicating that carbon has slight graphitization.

[0052] Figure 7 The thermoelectric properties of sample film1 as a function of temperature are shown. Its Seebeck coefficient at room temperature is -138 μVK. -1 The conductivity is 930 S cm⁻¹ -1 The power factor is 1761 μW / m.-1 K -2 .like Figure 7 As shown in (a), when the temperature increases from 300 K to 400 K, |α| decreases from 138 μV K. -1 Dropped to 82 μV K -1 σ then increases from 930 μV K -1 It rose rapidly to 2743S cm -1 This is due to the thermal excitation of charge carriers within the orthogonal silver selenide semiconductor (β-Ag₂Se). However, when the temperature reaches 410 K, |α| rapidly decreases to 28 μV K. -1 σ suddenly increases to 3635S cm -1 This is because β-Ag₂Se transforms into cubic silver selenide (α-Ag₂Se) at around 407 K (Tc), exhibiting typical half-metal characteristics. Finally, sample film1 achieves a maximum power factor (PF) of approximately 1955 μW / m² at about 360 K. -1 K -2 Considering the strong coupling between electrical properties and carrier concentration (n), Figure 7 (b) shows the temperature dependence of n and carrier mobility (μ) of sample film1. As temperature increases, n decreases from 0.6 × 10⁻⁶. 19 cm -3 Gradually increased to 2.8 × 10 19 cm -3 μ decreased from 968 to 615 cm 2 V -1 s -1 When the temperature exceeds Tc, n and μ decrease to 7.0 × 10⁻⁶. 19 cm -3 and 288cm 2 V -1 s -1 This abrupt change is due to α-Ag₂Se being a superionic conductor, in which Ag ions move freely, resulting in a high ion diffusion coefficient, thus causing strong electron scattering and a sudden decrease in μ. The κ value of a film 1 with a thickness of approximately 13 μm at room temperature is 0.66 W / m. -1 K -1 Calculations show that the room temperature ZT value of sample film1 is 0.81. Figure 7 As shown in (c), this value is one of the highest ZT values ​​reported in the literature for self-supporting flexible thermoelectric films.

[0053] The flexibility of sample film1 is as follows Figure 8As shown in (a), when sample film1 was bent 1000 times with a bending radius of 4 mm, its σ value decreased by only 2.8%. As the number of bends increased to 3000, the σ retention rate still exceeded 90%, demonstrating excellent flexibility. Figure 8 As shown in (b), the flexibility exhibited by sample film1 is competitive with that of flexible films (including substrate-supported films and self-supporting films) reported in the literature (e.g. Nat. Mater. 2019, 18, 62; Adv. Funct. Mater. 2022, 32, 2106902).

[0054] Figure 9 The output characteristics of the four-arm flexible thermoelectric device assembled using sample film1 are shown, including the open-circuit voltage (V) it produces. oc The voltage is linearly related to the temperature difference between the hot and cold ends of the device and is close to the theoretical open-circuit voltage. This can be achieved by adjusting the load resistance (R). L The output voltage (V) and output current (I) exhibit a linear relationship under different temperature differences. When R L When the total internal resistance (Ri) of the circuit is equal, the maximum output power is 2.0, 3.1, and 5.5 μW at ΔT values ​​of 18.5, 24.7, and 31.4 K, respectively, corresponding to power densities of 8.2, 13.1, and 22.9 W / m². -2 It exhibits excellent output characteristics. Furthermore, the flexibility of the fabricated thermoelectric device was tested by bending it along directions parallel (x-x') and perpendicular (y-y') to the arm length direction. The device was directly clamped with a polyimide film to avoid additional damage.

[0055] like Figure 10 As shown, regardless of whether the bending occurs in the x-x' or y-y' direction, the resistance change of the device when bent along a circular tube with a radius of 9 mm is greater than the resistance change when bent in the 18 mm direction. This is because the smaller the bending radius, the greater the bending stress. After 1000 bends along the x-x' or y-y' direction with a bending radius of 9 mm, the resistance change rates are 10.7% and 11.0%, respectively, indicating that the fabricated thermoelectric device has good flexibility.

[0056] Example 2:

[0057] The process was largely the same as in Example 1, except that the weight ratio of silver selenide powder to solvent was adjusted to 6:1. The prepared self-supporting flexible composite film had a Seebeck coefficient of -137 μV K at room temperature. -1 The conductivity is 798 Scm -1 The power factor is 1491 μW / m. -1 K -2 The decrease in its thermoelectric properties is mainly due to the increased porosity caused by the evaporation of more solvent, which in turn leads to poorer electrical properties.

[0058] Example 3:

[0059] The process was largely the same as in Example 1, except that the weight ratio of silver selenide powder to solvent was adjusted to 10:1. The prepared flexible composite film had a Seebeck coefficient of -133 μV K at room temperature. -1 The conductivity is 901 S cm⁻¹ -1 The power factor is 1591 μW / m. -1 K -2 Its power factor is among the highest reported for self-supporting flexible thermoelectric films.

[0060] Comparative Example 1:

[0061] Compared to Example 1, most aspects are the same, except that the room temperature Seebeck coefficient of the prepared self-supporting silver selenide / carbon composite flexible film is -135 μV K, except that the thermal annealing temperature is adjusted to 400°C. -1 The conductivity is 831 S cm⁻¹ -1 The power factor is 1524 μW / m. -1 K -2 The decrease in its thermoelectric properties is mainly due to the incomplete removal of solvent caused by the lower heat treatment temperature, the smaller size of silver selenide grains, and the higher defect content in the carbonized product of polyvinylpyrrolidone after the heat treatment temperature is lower, which leads to enhanced scattering of charge carriers and thus a decrease in electrical properties.

[0062] Comparative Example 2:

[0063] Compared with Example 1, most of the contents are the same, except that the flexible polyimide substrate is replaced with a nylon substrate. The nylon substrate curls and deforms at heat treatment temperatures above 250°C, causing the film to fail.

[0064] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric thin film, characterized in that, Includes the following steps: (1) Polyvinylpyrrolidone was added to ethylene glycol and heated and stirred to obtain a mixed solvent. Then, silver selenide powder was stirred with the mixed solvent to obtain a precursor slurry. (2) The precursor slurry is printed onto a polyimide substrate using screen printing technology and then dried to obtain a thin film precursor; (3) The film precursor is heated and annealed in a vacuum environment, then cooled to room temperature, and the substrate is peeled off to obtain the composite film, which is the target product. The ratio of polyvinylpyrrolidone to ethylene glycol is (1.5-2.5) g: 10 mL; In step (1), the mass ratio of silver selenide powder to mixed solvent is 6-10:1; In step (3), the substrate is peeled off, and the edge area with a width of 0.5 to 1.5 mm is first cut off; In step (3), the heating annealing temperature is 450℃ and the time is 2-3h.

2. The method for preparing a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric thin film according to claim 1, characterized in that, In step (1), the heating and stirring temperature is 60-80℃.

3. The method for preparing a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric thin film according to claim 1, characterized in that, In step (1), the stirring time of silver selenide powder and mixed solvent is 16 to 32 hours.

4. The method for preparing a high-performance self-supporting silver selenide / carbon composite flexible thermoelectric thin film according to claim 1, characterized in that, In step (2), the mesh size of the screen used in the screen printing technology is 250 mesh.

5. A high-performance self-supporting silver selenide / carbon composite flexible thermoelectric thin film, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. The application of the high-performance self-supporting silver selenide / carbon composite flexible thermoelectric film as described in claim 5 in flexible thermoelectric devices or portable wearable electronic devices.

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