CN115285946B - Ultra-high performance flexible silver selenide film with (201) dominant crystal plane orientation and power generation device - Google Patents

Abstract

The invention relates to an ultra-high performance flexible silver selenide film with (201) dominant crystal plane orientation and a power generation device. The flexible substrate is a flexible film, and Ag ₂ Se with a (201) crystal face as a dominant growth crystal face and penetrating columnar crystals is grown on the flexible substrate. The invention prepares the uniform silver selenide film with (201) dominant crystal plane orientation and excellent crystallinity quickly and controllably through the room temperature selenization reaction for the first time, the film power factor and the thermoelectric figure of merit can respectively reach the ultra-high value of 2590 mu W m ^‑1K^‑2 and 1.2, and the film is used as a thermoelectric arm for the first time to assemble a series of flexible film thermoelectric power generation devices, the power density of the devices reaches the ultra-high performance of 27.6+/-1.95 W.m ^‑2 (30K temperature difference) and 124+/-8.78 W.m ^‑2 (60K temperature difference) under the room temperature working condition, and the invention has wide commercialized application prospect.

Description

An ultra-high performance flexible silver selenide film with (201) dominant crystal plane orientation and a power generation device

Technical Field

The present invention belongs to the field of thermoelectric materials and power generation devices, and in particular relates to an ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation and a thermoelectric power generation device.

Background technique

Energy utilization is an inexhaustible driving force for human beings to maintain sustainable development. Wearable devices can make humans part of the Internet of Things (IoT) and show great commercial prospects. However, due to the limited life of various batteries, it is facing great challenges to continuously power wearable or embedded devices. As an emerging energy harvesting tool, thermoelectric generators (TEGs) convert heat into electrical energy in a unique way and are becoming the best choice to achieve this goal. Several indicators such as the zT value, PF (power factor) and MOPD (maximum output power density) of related semiconductor materials or actual power generation devices reflect the influence of different microstructure materials on thermoelectric performance from different aspects. According to the well-known formula (PF = S ² σ and zT = S ² σTκ ^-1 ), the ideal situation is to obtain higher S (Seebeck coefficient) and σ (conductivity), but keep low κ (thermal conductivity) at the same time. However, it is very difficult to optimize these factors simultaneously in practical applications because the two key factors, S as the numerator and κ as the denominator, often change in the same direction. Worse still, the Seebeck coefficient, which is the square term in the formula, changes in the opposite direction to the carrier mobility, which is another key factor that positively affects σ. Despite this, efforts to find new materials and more efficient preparation strategies have never stopped.

In the past few decades, many traditional bulk chalcogenide compounds have been explored to meet the requirements of high zT values, such as Bi ₂ Te ₃ , Bi ₂ Se ₂ , Bi _0.5 Sb _1.5 Te ₃ , TiS ₂ and Sb ₂ Se ₂ , etc., to achieve the task of thermoelectric conversion near room temperature, among which some compounds such as Bi ₂ Te ₃ have been used in commercial products. Considering that the rigid properties of bulk materials limit their further application in F-TEGs (flexible thermoelectric generators), thin film chalcogenides have pointed out the prospects for future artificial intelligence and wearable devices with their high thermoelectric conversion performance and flexibility. Obviously, the most ideal state for future flexible wearable devices is to work at room temperature. Group I-VI (especially Ag-Se-based) compounds are a promising class of chalcogenides that have emerged recently, showing significant advantages as flexible TEGs at room temperature and have received great attention. For example, the n-type narrow bandgap semiconductor β-Ag ₂ Se (Eg = ∼0.04-0.2 eV) is considered a promising F-TEG due to its excellent room-temperature thermoelectric performance and good flexibility. In particular, Ag ₂ Se with a 2:1 Ag/Se molar stoichiometry has been demonstrated by several research groups to exhibit the best performance among various Ag-Se ratios.

Prior art reports have reported polycrystalline Ag ₂ Se bulk materials obtained by direct reaction of elemental silver and selenium at 1000°C (10 ^-4 Torr) for 10 hours. In addition, Cai and colleagues reported in Nature Communications a Ag ₂ Se F-TEG (film thickness of about 10 μm) prepared by hot pressing at 200°C and 24 MPa, with a high power factor of about 987.4 μW m ^-1 K ^-2 , an estimated zT of 0.6 at 300K, and the PF value was further increased to 2231.5 μW m ^-1 K ^-2 by Cu/AgCuSe incorporation. However, almost all the selenization strategies reported so far inevitably require relatively high temperatures (>130°C, the phase transition temperature from α phase to β phase), or high pressure or vacuum conditions, which are also not conducive to the further commercialization of Ag ₂ Se materials. In addition, if the film thickness can be further reduced, it will not only reduce the cost, but also be beneficial to the flexibility of the film product.

In 2013, our research group applied for an invention patent with application number 201310090546.6, and the invention name is: a chemical method for in-situ synthesis of Ag ₂ Se semiconductor photoelectric thin film materials at room temperature. The elemental Se powder is dissolved in an aqueous solution of Na ₂ S to form an orange-yellow solution, and then a substrate material with a certain thickness of elemental silver film sputtered on the surface and the above solution are placed in the same container. The solution is added first and then the substrate material is added, and it is ensured that these substrate materials are immersed below the liquid surface. The reaction is carried out in the temperature range of 7 to 35°C, and the reaction time varies according to the actual situation (under different conditions, the reaction time varies within 1.5min to 3h). After the reaction is completed, a silver-gray Ag ₂ Se semiconductor photoelectric thin film material can be prepared in situ on the substrate surface. The obtained product is washed with deionized water and dried at 80°C.

In the present application, the applicant has conducted a large number of experiments and regulated the selenization reaction conditions in many aspects, and achieved the controllable preparation of a uniform silver selenide film with (201) dominant crystal plane orientation and excellent crystallinity. This film is directly used as a thermoelectric arm to prepare a series of flexible thin-film thermoelectric power generation devices in situ. The device power density reaches 27.6±1.95W·m ^-2 (30K temperature difference) and 124±8.78W·m ^-2 (30K temperature difference) under room temperature working conditions. Ultra-high performance, it has broad prospects for commercial applications.

Summary of the invention:

The technical problem to be solved by the present invention is: in view of the shortcomings of the prior art, an ultra-high performance flexible silver selenide film and a power generation device with a (201) dominant crystal plane orientation are provided.

The technical solution adopted by the present invention for the problem to be solved is:

Provided is an ultra-high performance flexible silver selenide film with (201) dominant crystal plane orientation. The film is a flexible film on which Ag ₂ Se with (201) crystal plane as the dominant growth crystal plane and columnar crystals running through it is grown on a flexible substrate.

According to the above scheme, the thickness of the flexible silver selenide film is 600-1400nm, the surface is uniform, and the crystallinity is excellent.

A method for in-situ large-area controlled synthesis of an ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation based on a single silver film is provided, wherein single Se powder is dissolved in an aqueous solution of Na2S to form a deep red solution, and then a single silver film with a silver thickness of 250 to 450 nm is immersed in the solution to react and synthesize an ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation.

According to the above scheme, the single-element silver film adopts a flexible substrate.

In the above scheme, the silver thin film forming method used is DC magnetron sputtering or silver mirror reaction wet chemical method.

In the above solution, the substrate material is flexible PI (polyimide).

In the above scheme, the Se source is in excess.

In the above scheme, the molar ratio of Se/S in the sodium sulfide/Se powder aqueous solution is 1:1-2:1.

In the above scheme, the reaction temperature is selected in the range of 20-40°C; the reaction time is 15 seconds to 60 seconds.

According to the above scheme, after the reaction is completed, it is washed with deionized water and dried naturally. The obtained silver selenide film sample is gray-black.

Provided is the application of the ultra-high performance flexible silver selenide film with (201) dominant crystal plane orientation as a thermoelectric power generation device.

Provided is a flexible thin-film thermoelectric power generation device which is prepared by directly using the highly oriented flexible silver selenide thermoelectric film penetrated by the synthesized columnar crystals as the thermoelectric arm.

According to the above scheme, the above method includes placing the silver selenide film prepared above into a thermal evaporator, using a mask plate to deposit gold electrodes at both ends of each silver selenide film, directly making thermoelectric arms, and making power generation devices.

According to the above scheme, multiple, for example, 4 silver selenide films are connected in series to form a silver selenide single-arm temperature difference power generation device. For example, 4 silver selenide films are placed side by side, gold electrodes are deposited at both ends, and then connected in series with silver paste, with one end as the cold end and the other end as the hot end, to assemble the power generation device.

The present invention controls the thickness of the initial silver single substance film, the Se content, the Se/S molar ratio, etc., and further selects a flexible substrate, and the selenization reaction is carried out simultaneously from the upper and lower interfaces of the single substance Ag film. Through the room temperature selenization reaction, a gray-black flexible silver selenide film with a thickness of 600-1400 nanometers, a (201) dominant crystal plane orientation, a uniform surface, and excellent crystallinity can be prepared. The reaction is rapid, which is conducive to obtaining a firmly bonded silver selenide film, and the reaction time is short, which is convenient for commercial use.

The present invention is the first to rapidly and controllably prepare uniform silver selenide thin films with (201) dominant crystal plane orientation and excellent crystallinity through room temperature selenization reaction. The power factor and thermoelectric figure of merit of the film can reach ultra-high values of 2590μW m ^-1 K ^-2 and 1.2 respectively. For the first time, the film is directly used as a thermoelectric arm to assemble a series of flexible thin film thermoelectric power generation devices. The device power density reaches ultra-high performance of 27.6±1.95W·m ^-2 (30K temperature difference) and 124±8.78W·m ^-2 (60K temperature difference) under room temperature working conditions. The method is simple to operate and does not require complex processes such as high temperature, high pressure, forging and pressing. It is low-cost and low-energy, and has broad industrial application prospects. It overcomes the shortcomings of the current _Ag2Se thermoelectric material preparation selenization strategy, which requires relatively high temperature (>130℃, phase transition temperature from α phase to β phase), long reaction time, and high pressure or vacuum conditions, and solves the problems of poor crystallinity and tendency and low thermoelectric performance.

Advantages of the present invention:

1. Silver selenide film has obvious (201) dominant crystal plane orientation, uniform surface and excellent crystallinity. Compared with the film without (201) dominant crystal plane orientation, the thermoelectric performance (ZT value and PF value) is greatly improved. The optimized film power factor (PF value) and thermoelectric figure of merit (zT) can reach ultra-high values of 2590μWm ^- 1K ^-2 and 1.2 respectively.

2. The method of the present invention can in-situ control the synthesis of ultra-high performance flexible silver selenide thin films with obvious (201) dominant crystal plane orientation, and can well control the morphology, size, thickness, and crystal phase of the Ag ₂ Se thin film material to obtain a crystal film with highly oriented columnar crystals running through it.

The macroscopic geometry of the in-situ prepared thin film is controllable, which enables the fabrication of large-scale devices with high repeatability of device performance;

The invention can control the synthesis over a large area in situ; the reaction is fast, and the reaction in room temperature aqueous solution can be completed within 1 minute; the operation is simple, and it is conducive to obtaining a firmly bonded silver selenide film; it meets the needs of industrial applications and is green and environmentally friendly.

3. Based on the above-mentioned flexible silver selenide film directly used as a series of flexible thin film thermoelectric power generation devices assembled as thermoelectric arms, the device power density under room temperature working conditions is greatly improved compared with the thermoelectric devices prepared with silver selenide without (201) dominant crystal plane orientation. The optimized device power density reaches ultra-high performance of 27.6±1.95W·m ^-2 (30K temperature difference) and 124±8.78W·m ^-2 (30K temperature difference).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a physical picture of a gray-black silver selenide film obtained by in-situ selenization reaction at room temperature;

FIG2 is an X-ray powder diffraction diagram of a silver selenide film obtained by depositing a 150 nm silver film in Comparative Example 1;

Figures 3-4 are scanning electron microscope surface and cross-sectional morphologies of the silver selenide film obtained in Comparative Example 1;

FIG5 is a diagram showing the maximum output power of the silver selenide film obtained in Comparative Example 1;

FIG6 is a graph showing the maximum output power density of the silver selenide film obtained in Comparative Example 1;

FIG7 is an X-ray powder diffraction diagram of a silver selenide film obtained by depositing a 250 nm silver film in Example 1;

Fig. 8-Fig. 9 are scanning electron microscope images of the silver selenide film obtained in Example 1;

FIG10 is a diagram showing the maximum output power of the silver selenide film obtained in Example 1;

FIG11 is a diagram showing the maximum output power density of the silver selenide film obtained in Example 1;

FIG12 is an X-ray powder diffraction diagram of a silver selenide film obtained by depositing a 350 nm silver film in Example 2;

Figures 13-14 are scanning electron microscope surface and cross-sectional morphologies of the silver selenide film obtained in Example 2;

FIG15 is a cross-sectional coaxial transmission backscattered electron diffraction image of the silver selenide film obtained in Example 2;

FIG16 is a diagram showing the maximum output power of the silver selenide film obtained in Example 2;

FIG17 is a diagram showing the maximum output power density of the silver selenide film obtained in Example 2;

FIG18 is an X-ray powder diffraction pattern of a silver selenide film obtained by depositing a 450 nm silver film in Example 3;

Figures 19-20 are scanning electron microscope images of the silver selenide film obtained in Example 3;

FIG21 is a diagram showing the maximum output power of the silver selenide film obtained in Example 3;

FIG22 is a diagram showing the maximum output power density of the silver selenide film obtained in Example 3.

FIG23 : SEM-EDS spectrum of the solid powder residue after the Se/Na ₂ S aqueous solution reacted with Ag (corresponding to P-1000) was naturally dried;

Figure 24. Device diagram of a silver selenide single-arm temperature difference generator.

Detailed ways:

The present invention synthesizes a highly oriented flexible silver selenide thermoelectric film and a power generation device with columnar crystals in-situ and in large areas based on a single silver film. By adjusting the initial single silver film thickness, substrate type, Se content, reaction time and other parameters, the selenization reaction can be carried out simultaneously from the upper and lower interfaces of the single Ag film. A gray-black flexible silver selenide film with a thickness of 600-1400 nanometers, a (201) dominant crystal plane orientation, a uniform surface and excellent crystallinity is quickly and controllably prepared on a PI (polyimide) substrate through a room temperature selenization reaction, and a series of flexible thin film thermoelectric power generation devices are prepared in-situ.

Further, gold electrodes were deposited at both ends of each silver selenide film using a mask plate, directly used as four thermoelectric arms, and four silver selenide films were placed side by side up and down, connected in series with silver paste, and then one end was used as the cold end and the other end as the hot end to assemble a silver selenide single-arm temperature difference power generation device. The effective length of the silver selenide thermoelectric arm was controlled to be 14mm. The temperature difference at both ends of the device was controlled to evaluate its actual output performance.

Example 1

(1) Preparation of single silver thin film

A silver film of about 250 nm was deposited on a polyimide (PI) substrate using a DC magnetron sputtering method. The sputtering current was 40 mA, the sputtering vacuum was 4×10 ^-3 mbar, and the thickness of the sputtered silver film was controlled using a film thickness monitor. During the sputtering process, a mask was used to control the size of the deposited silver film. Finally, the single silver film deposited on the surface of the PI substrate was 4 parallel rectangles. Each rectangle was 16 mm long and 5 mm wide, and the interval between the rectangles was 5 mm.

(2) Preparation of silver selenide thin films and evaluation of thermoelectric properties

At 25°C and normal pressure, weigh 0.6g Na ₂ S·9H ₂ O and add it to 20mL deionized water to dissolve, then add 0.2g Se powder and stir to dissolve it to obtain a deep red solution. Then immerse the above-prepared single silver film in the solution and react for about 20s to completely convert the silver into silver selenide. After completion, wash with deionized water and dry naturally. During the reaction, it can be observed that the selenization reaction proceeds simultaneously from the upper and lower interfaces of the single Ag film, and the obtained silver selenide film sample is gray-black, as shown in Figure 1. Figure 7 is the XRD diagram of the obtained sample, and its PDF card number is: 71-2410. The test results show that the prepared thin film material is highly matched with β-phase silver selenide and shows a strong (201) crystal plane orientation; Figures 8 and 9 are SEM images of the obtained samples. The test results show that the thickness of the sample is 600nm. The silver selenide thin film material is composed of large micron-sized grains interwoven with each other. The film has good density from a microscopic level and has abundant interfaces between the grains. Characterization by cross-sectional coaxial transmission backscattered electron diffraction shows that the silver selenide film is a columnar crystal. The sample XRD and the SEM-EDS spectrum of the solid powder residue after the Se/Na2S aqueous solution reacting with Ag is naturally dried, and the silver in the silver single substance film is completely converted and the reaction is complete.

After measurement, the prepared silver selenide thin film material has a Seebeck coefficient of -129μV/K at 300K, an electrical conductivity of 1440S/cm, a thermal conductivity of 0.74W/(m·K), a power factor of 2400μW/(m·K), and a thermoelectric figure of merit of approximately 0.97.

(2) Assembly and performance evaluation of silver selenide single-arm thermoelectric generator devices

The silver selenide film prepared above was placed in a thermal evaporator, and gold electrodes were deposited at both ends of each silver selenide using a mask, and the effective length of the silver selenide thermoelectric arm was controlled to be 14 mm. Four silver selenide thermoelectric arms were connected in series using room temperature cured silver paste to assemble a silver selenide single-arm thermoelectric generator device, as shown in Figure 24. The temperature difference at both ends of the device was controlled to evaluate its actual output performance. The cold end temperature was controlled to be 25°C, and the hot end temperature was increased from 35°C to 85°C, with a temperature interval of 10°C. The output of the device was measured using a digital source meter, as shown in Figures 10 and 11. Under the temperature difference conditions of 10°C to 60°C, the corresponding maximum output powers were 19.6, 118, 313, 580.7, 925 and 1346.8 nW, respectively, and the corresponding maximum output power densities were 1.66, 10.05, 26.56, 49.28, 78.5 and 114.29 W/m ² , respectively.

Example 2

(1) Preparation of single silver thin film

A 350nm silver film was deposited on a polyimide (PI) substrate using a DC magnetron sputtering method. The sputtering current was 40mA, the sputtering vacuum was 4×10 ^-3 mbar, and the thickness of the sputtered silver film was controlled using a film thickness monitor. During the sputtering process, a mask was used to control the size of the deposited silver film. Finally, the single silver film deposited on the surface of the PI substrate was 4 parallel rectangles. Each rectangle was 16mm long and 5mm wide, and the interval between the rectangles was 5mm.

(2) Preparation of silver selenide thin films and evaluation of thermoelectric properties

At 25°C and normal pressure, weigh 0.6g Na ₂ S·9H ₂ O and add it to 20mL deionized water to dissolve, then add 0.2g Se powder and stir to dissolve it to obtain a deep red solution. Then immerse the above-prepared single silver film in the solution and react for about 30s to completely convert the silver into silver selenide. After completion, wash it with deionized water and dry it naturally. The obtained silver selenide film sample is gray-black. Figure 12 is the XRD diagram of the obtained sample, and its PDF card number is: 71-2410. The test results show that the prepared film material is highly matched with β-phase silver selenide and shows a strong (201) crystal plane orientation; Figures 13 and 14 are SEM images of the obtained samples. The test results show that the thickness of the sample is 1000nm. The silver selenide film material is composed of large micron-sized grains interwoven with each other. The film has good density from the microscopic level and has abundant interfaces between the grains. Figure 15 is a cross-sectional coaxial transmission backscattered electron diffraction band contrast image of the obtained sample, from which it can be seen that the silver selenide film is a columnar through-crystal. Characterized by the sample XRD and the SEM-EDS spectrum of the solid powder residue after the Se/Na ₂ S aqueous solution reacting with Ag (corresponding to P-1000) is naturally dried (as shown in Figure 23), the silver in the silver single substance film is completely converted and the reaction is complete.

After measurement, the prepared silver selenide thin film material has a Seebeck coefficient of -134μV/K at 300K, an electrical conductivity of 1440S/cm, a thermal conductivity of 0.66W/(m·K), a power factor of 2590μW/(m·K), and a thermoelectric figure of merit of approximately 1.2.

(3) Assembly and performance evaluation of silver selenide single-arm thermoelectric generator devices

The silver selenide film prepared above was placed in a thermal evaporator, and gold electrodes were deposited at both ends of each silver selenide using a mask, and the effective length of the silver selenide thermoelectric arm was controlled to be 14 mm. Four silver selenide thermoelectric arms were connected in series using room temperature cured silver paste to assemble a silver selenide single-arm thermoelectric generator device. The temperature difference at both ends of the device was controlled to evaluate its actual output performance. The cold end temperature was controlled to be 25°C, and the hot end temperature was increased from 35°C to 85°C with a temperature interval of 10°C. The output of the device was measured using a digital source meter, as shown in Figures 16 and 17. Under the temperature difference conditions of 10°C to 60°C, the corresponding maximum output powers were 36.6, 241, 576, 1120, 1790 and 2580 nW, respectively, and the corresponding maximum output power densities were 1.75, 11.5, 27.6, 53.5, 85.6 and 124 W/m ² , respectively.

Example 3

(1) Preparation of single silver thin film

A silver film of about 450nm was deposited on a polyimide (PI) substrate by direct current magnetron sputtering, with a sputtering current of 40mA and a sputtering vacuum of 4×10 ^-3 mbar. The thickness of the sputtered silver film was controlled by film thickness monitoring. During the sputtering process, a mask was used to control the size of the deposited silver film. Finally, the single silver film deposited on the surface of the PI substrate was 4 parallel rectangles. Each rectangle was 16mm long and 5mm wide, and the interval between the rectangles was 5mm.

(2) Preparation of silver selenide thin films and evaluation of thermoelectric properties

At 25°C and normal pressure, weigh 0.6g Na2S·9H2O and add it to 20mL deionized water to dissolve, then add 0.2g Se powder and stir to dissolve it to obtain a deep red solution. Then immerse the above-prepared single silver film in the solution and react for about 40s to completely convert the silver into silver selenide. After completion, wash it with deionized water and dry it naturally. The obtained silver selenide film sample is gray-black. Figure 18 is the XRD diagram of the obtained sample, and its PDF card number is: 71-2410. The test results show that the prepared film material is highly matched with β-phase silver selenide and shows a strong (201) crystal plane orientation; Figures 19 and 20 are SEM images of the obtained samples. The test results show that the thickness of the sample is 1400nm. The silver selenide film material is composed of large micron-sized grains interwoven with each other. The film has good density from the microscopic level and has rich interfaces between the grains. The cross-sectional coaxial transmission backscattered electron diffraction characterization shows that the silver selenide film is a columnar through-crystal. The sample XRD and the SEM-EDS spectrum of the solid powder residue after the Se/Na2S aqueous solution reacting with Ag is naturally dried show that the silver in the silver single substance film is completely converted and the reaction is complete.

After measurement, the prepared silver selenide thin film material has a Seebeck coefficient of -138μV/K at 300K, an electrical conductivity of 1230S/cm, a thermal conductivity of 0.76W/(m·K), a power factor of 2340μW/(m·K), and a thermoelectric figure of merit of approximately 0.92.

(2) Assembly and performance evaluation of silver selenide single-arm thermoelectric generator devices

The silver selenide film prepared above was placed in a thermal evaporator, and gold electrodes were deposited at both ends of each silver selenide using a mask, and the effective length of the silver selenide thermoelectric arm was controlled to be 14 mm. Four silver selenide thermoelectric arms were connected in series using room temperature cured silver paste to assemble a silver selenide single-arm thermoelectric generator device. The temperature difference at both ends of the device was controlled to evaluate its actual output performance. The cold end temperature was controlled to be 25°C, and the hot end temperature was increased from 35°C to 85°C with a temperature interval of 10°C. The output of the device was measured using a digital source meter, as shown in Figures 21 and 22. Under the temperature difference of 10°C to 60°C, the corresponding maximum output powers were 41.8, 268.4, 706.7, 1308.4, 2060 and 2927 nW, respectively, and the corresponding maximum output power densities were 1.40, 9.01, 23.74, 43.95, 69.20 and 98.32 W/m ² , respectively.

At the same time, we studied different initial silver film thicknesses and other different conditions and found that the process reaction conditions of the present invention have an important influence on the successful synthesis of the target product.

For example, the initial silver film thickness affects the crystal orientation of the target product: a single silver film is prepared according to the reference example method, and the initial thickness of the silver film is 150nm; at 25°C and normal pressure, 0.6g Na ₂ S·9H ₂ O is weighed and added to 20mL deionized water to dissolve, and then 0.2g Se powder is added thereto and stirred to dissolve, obtaining a deep red solution. Then the single silver film prepared above is immersed in the solution, and the silver element is completely converted into silver selenide after the reaction. After the reaction is completed, it is washed with deionized water and dried naturally. The obtained silver selenide film sample is gray-black. Figure 2 is the XRD diagram of the obtained sample, and its PDF card number is: 71-2410. The test results show that the prepared film material is highly matched with β-phase silver selenide and shows a strong (121) crystal orientation; Figures 3 and 4 are SEM images of the obtained sample, and the test results show that the thickness of the sample is 550nm. After measurement, the Seebeck coefficient of the silver selenide thin film material at 300K is -138μV/K, the electrical conductivity is 856S/cm, the thermal conductivity is 1.13W/(m·K), the power factor is 1630μW/(m·K), and the thermoelectric figure of merit is about 0.43. The performance is significantly worse than that of the silver selenide thin film material synthesized in Examples 1-3.

Claims (9)

1. An ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation, characterized in that: it is a flexible film, Ag ₂ Se with a (201) crystal plane as a dominant growth crystal plane and columnar crystals running through it is grown on a flexible substrate, and the preparation method is: dissolving a single substance Se powder in an aqueous solution of Na ₂ S to form a deep red solution, wherein: the Se/S molar ratio in the sodium sulfide/Se powder aqueous solution is 1:1-2:1, and then immersing a single substance silver film with a silver thickness of 250-450nm into the solution to react and synthesize an ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation. 2. The silver selenide film according to claim 1 is characterized in that the flexible silver selenide film has a thickness of 600-1400 nm, a uniform surface, and excellent crystallinity. 3. A method for synthesizing the ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation as claimed in claim 1 based on a single silver film, characterized in that: single Se powder is dissolved in an aqueous solution of _Na2S to form a deep red solution, wherein: the Se/S molar ratio in the sodium sulfide/Se powder aqueous solution is 1:1-2:1, and then a single silver film with a silver thickness of 250~450nm is immersed in the solution to react and synthesize an ultra-high performance flexible silver selenide film with a (201) dominant crystal plane orientation. 4. The method according to claim 3 is characterized in that: the single-substance silver thin film adopts a flexible substrate, and the single-substance silver thin film forming method used is a DC magnetron sputtering or a silver mirror reaction wet chemical method. 5. The method according to claim 3, characterized in that the substrate material is flexible PI polyimide. The method according to claim 3 , characterized in that the Se source is excessive. 7. The method according to claim 3, characterized in that: the reaction temperature is selected in the range of 20-40°C; and the reaction time is 15 seconds to 60 seconds. 8. Use of the ultra-high performance flexible silver selenide film described in claim 1 as a thermoelectric power generation device. 9. A flexible thin-film thermoelectric power generation device prepared by directly using the ultra-high performance flexible silver selenide thermoelectric film described in claim 1 as a thermoelectric arm.