Large-grain cadmium telluride thin film and method of making same

Abstract

The application provides a large-grain cadmium telluride film and a preparation method thereof, and relates to the technical field of solar cell devices. The invention uses a three-step growth method, first generates a template for the growth of large-grain cadmium telluride by a two-step method, and then performs secondary epitaxial deposition of cadmium telluride to obtain a large-grain cadmium telluride film. The grain size of the obtained large-grain cadmium telluride is 50-200 mu m, the average grain size is 95-155 mu m, and the variation coefficient of the grain size is less than 15%. The method solves the problems of slow growth rate of the epitaxial cadmium telluride film and high cost of large-scale production. At the same time, the problems of small, uneven and non-regrowth of the polycrystalline cadmium telluride film in the existing cadmium telluride film solar cell technology, which leads to low minority carrier lifetime, are solved.

Description

Technical Field

[0001] This application relates to the technical field of solar cell devices, and in particular to a large-grain cadmium telluride thin film and its preparation method. Background Technology

[0002] Cadmium telluride (CdT) has a band gap of approximately 1.45 eV and is commonly used as a p-type absorber layer material. This band gap is close to the ideal band gap corresponding to the theoretical maximum efficiency of a single-junction solar cell, thus possessing the potential to achieve high photoelectric conversion efficiency. CdT also has a sufficiently large absorption coefficient, meaning that a thickness of approximately 3 μm is sufficient to absorb the vast majority of the visible solar spectrum. In contrast, traditional crystalline silicon photovoltaics require silicon wafers that are 150–200 μm thick.

[0003] However, cadmium telluride is typically deposited rapidly on transparent conductive oxide (TCO) / glass substrates in a supersaturated cadmium and tellurium vapor environment. This results in a small critical nucleus size, a high nucleation rate, and a small internucleation distance, leading to the formation of fine grains in the thin film. The resulting grain boundary recombination limits the improvement of battery performance. Grain boundaries, as one of the main nonradiative recombination centers for charge carriers, hinder the collection and transport of charge carriers.

[0004] Larger grains can reduce nonradiative recombination at grain boundaries, effectively improving the transport and collection of photogenerated carriers, thereby enhancing the photoelectric conversion efficiency of the device.

[0005] According to the applicant's understanding, the literature reports related to large-grain cadmium telluride thin films currently include: 1) Chinese patent CN112095151 A discloses a method for obtaining large-grain quasi-single-crystal metal thin films by using tensile stress to induce plastic deformation in metal thin films, but the surface of the grains obtained by this method is prone to wrinkling and unevenness. 2) Chinese patent CN 110534654 A discloses a method for promoting the formation of large-grain thin films from monolayer perovskite thin films in a closed space. The temperature used in this patent is below 400℃, and no high-pressure environment is used. For organic-inorganic hybrid perovskite thin films, their melting and boiling points are low, and their ion mobility is high. Ion migration and grain regrowth can be completed under relatively low temperature and pressure environments. However, inorganic covalent compound thin films such as cadmium telluride have high melting and boiling points and low atomic mobility. Under the growth conditions disclosed in the above patents, grain regrowth cannot be completed.

[0006] Therefore, this application proposes a three-step method to generate large-grain cadmium telluride thin films, including two steps for preparing a seed layer. This method is simple and easy to operate, and the generated cadmium telluride grains are large in size and have good uniformity, which reduces the non-radiative recombination centers at the grain boundaries and improves the photoelectric conversion efficiency of solar cells. Summary of the Invention

[0007] The purpose of this application is to provide a large-grain cadmium telluride thin film and its preparation method to improve the problem of low photoelectric conversion efficiency of existing solar cell devices.

[0008] To achieve the above objectives, this application provides the following technical solution: On the one hand, this application provides a large-grain cadmium telluride thin film, including cadmium telluride grains, wherein the large-grain cadmium telluride grains have a size of 50~200μm, an average grain size of 95~155μm, and a grain size variation coefficient of less than 15%.

[0009] Furthermore, the thickness of the large-grain cadmium telluride film is 2~10μm, and the grains have a columnar crystal morphology.

[0010] Furthermore, the large-grain cadmium telluride thin film has (111), (220), and (311) diffraction peaks in the X-ray diffraction pattern, wherein the diffraction intensities of the (220) and (311) diffraction peaks are 5% to 20% of the diffraction intensity of the (111) derived peak, respectively.

[0011] Furthermore, the minority carrier lifetime of the large-grain cadmium telluride thin film is greater than 300 ns.

[0012] On the other hand, this application also provides a method for preparing large-grain cadmium telluride thin films, comprising the following steps: S1. Deposit a 100~500nm cadmium telluride seed layer on the surface of the window layer with a transparent substrate. The deposition temperature is 400~600℃, the source temperature is 600~800℃, and the pressure is 100~2000Pa.

[0013] S2. The cadmium telluride seed layer is annealed under high temperature and high pressure at a temperature of 400~600℃, an annealing pressure of 10~30MPa, and a holding time of 0.5~3h. After annealing, the size of the seed layer grains is 50~200μm, the average grain size is 95~155μm, and the thickness is 100~500nm. S3. Under the conditions of substrate temperature of 400~600℃, source temperature of 600~800℃, and pressure of 100~2000Pa, secondary epitaxial deposition of cadmium telluride is carried out on the seed layer as a substrate to obtain a large-grain cadmium telluride thin film.

[0014] Furthermore, in S3, the cadmium telluride film is deposited on the seed layer at a rate of 0.05~1 μm / min.

[0015] Furthermore, in S1 and / or S3, the heating rate of the source and the substrate is 1~100℃ / min, and the pressure increase rate is 0.1~100 Pa / min. Furthermore, in S2, the heating rate is 0.1~5℃ / min, and the pressure increase rate is 0.1~2 MPa / min.

[0016] Furthermore, the methods used for depositing the seed layer in S1 and the secondary epitaxial deposition of cadmium telluride in S3 are selected from at least one of near-space sublimation (CSS), vapor transport, thermal evaporation, and sputtering.

[0017] Furthermore, the transparent substrate is selected from at least one of soda-lime glass, borosilicate glass, and flexible polymer substrate; Furthermore, the window layer is selected from one or more combinations of metal oxides, metal nitrides, cadmium sulfide, cadmium selenide, and cadmium telluride selenide.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The large-grain cadmium telluride thin film provided by this invention features large cadmium telluride grains with a small coefficient of variation and good grain uniformity. This effectively reduces grain boundary density and significantly decreases carrier recombination at grain boundaries, contributing to improved minority carrier lifetime and photoelectric conversion efficiency of corresponding solar cell devices. Furthermore, this invention provides a deposition method for large-grain cadmium telluride thin films, enabling rapid growth of micron-thickness films. Under high temperature and pressure, a seed layer of small grains hundreds of nanometers thick is forced to undergo grain diffusion and fusion, growing into a large-grain template. Micron-thickness large-grain cadmium telluride thin films are then rapidly epitaxially deposited on this template using near-space sublimation. This method improves the production efficiency of preparing epitaxial large-grain thin films. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the preparation method of the large-grain cadmium telluride thin film provided by the present invention. Figure 2 This is a structural diagram of the cadmium telluride solar cell device provided by the present invention; Figure 3 This is a distribution diagram of the large-grain cadmium telluride grain size in Example 1 of the present invention; Figure 4 This is a distribution diagram of the large-grain cadmium telluride grain size in Example 2 of the present invention; Figure 5This is a distribution diagram of the large-grain cadmium telluride grain size in Example 3 of the present invention; Figure 6 The images show the XRD patterns of the samples from Example 1 and Comparative Example 1 of this invention (A is the XRD result of the large-grain cadmium telluride film in Example 1, and B is the XRD result of the large-grain cadmium telluride film in Comparative Example 1). Figure 7 This invention illustrates the effect of cadmium telluride grain size on minority carrier lifetime and conversion efficiency in the embodiments and comparative examples.

[0021] See attached Figure 2 The structure includes a glass substrate 201, a transparent conductive film 202, a window layer 203, a cadmium telluride absorber layer 204, a back contact layer 205, and a metal electrode layer 206. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a large-grain cadmium telluride thin film, comprising cadmium telluride grains, wherein the large-grain cadmium telluride grains have a size of 50~200μm, an average grain size of 95~155μm, and a grain size variation coefficient of less than 15%.

[0024] Preferably, the large-grain cadmium telluride has a grain size of 80~190μm and an average grain size of 100~152μm.

[0025] Understandably, the grain size of large-grain cadmium telluride refers to the grain size in the lateral direction (the extension direction of the large-grain cadmium telluride film), and the average grain size refers to the average value of the lateral grain size. A lateral grain size within the aforementioned range ensures a sufficiently large grain size and its uniform distribution, effectively reducing the number of grain boundaries, thereby improving minority carrier lifetime and increasing battery conversion efficiency. The coefficient of variation of cadmium telluride grain size is the ratio of the standard deviation of grain size to the average grain size. The coefficient of variation is a quantitative indicator of the uniformity of grain size or the relative dispersion of grain size distribution. The coefficient of variation of the grain size in this invention is less than 15%, indicating that the large-grain cadmium telluride has a highly consistent grain size and good uniformity, effectively ensuring an ideal average grain size, effectively reducing the number of grain boundaries, and thus reducing non-radiative recombination of charge carriers at grain boundaries.

[0026] In some embodiments, the thickness of the large-grain cadmium telluride film is 2~10 μm, and the grains have a columnar crystal morphology.

[0027] Preferably, the thickness of the large-grain cadmium telluride film is 3~4 μm.

[0028] Understandably, the thickness of a large-grain cadmium telluride film can be interpreted as the longitudinal dimension of the large-grain cadmium telluride grains. The reason for controlling the thickness of the large-grain cadmium telluride film to be 2–10 μm is that this thickness range matches the light absorption depth of the cadmium telluride material, enabling effective absorption of over 95% of incident photons. Simultaneously, it allows the vast majority of photogenerated carriers to be effectively collected by the electrodes within a distance smaller than their diffusion length, thereby minimizing bulk recombination losses.

[0029] In some embodiments, the large-grain cadmium telluride thin film has (111), (220), and (311) diffraction peaks in the X-ray diffraction pattern, wherein the diffraction intensities of (220) and (311) are 5% to 20% of the diffraction intensity of (111).

[0030] Understandably, the cadmium telluride large-grain thin film in this invention exhibits strong preferential growth in the (111) plane direction, demonstrating effective grain growth and a significant improvement in crystal quality.

[0031] In some embodiments, the minority carrier lifetime of the large-grain cadmium telluride thin film is greater than 300 ns.

[0032] Understandably, the grain boundary density of large-grain thin films is effectively reduced, which effectively suppresses grain boundary recombination of minority carriers, thereby improving minority carrier lifetime.

[0033] This application also provides a method for preparing large-grain cadmium telluride thin films, comprising the following three steps: S1. Deposit a 100~500nm cadmium telluride seed layer on the surface of the window layer with a transparent substrate. The substrate temperature for depositing the seed layer is 400~600℃, the source temperature is 600~800℃, and the pressure is 100~2000Pa. S2. The cadmium telluride seed layer is annealed under high temperature and high pressure at a temperature of 400~600℃, an annealing pressure of 10~30MPa, and a holding time of 0.5~3h. After annealing, the size of the seed layer grains is 50~200μm, the average grain size is 95~155μm, and the thickness is 100~500nm. S3. Under the conditions of substrate temperature of 400~600℃, source temperature of 600~800℃, and pressure of 100~2000Pa, secondary epitaxial deposition of cadmium telluride is carried out on the seed layer as a substrate to obtain a large-grain cadmium telluride thin film.

[0034] Understandably, the purpose of step S1 is to deposit a cadmium telluride seed layer on the window layer, the thickness of which is 100-500 nm. This thickness range is limited because: if the thickness is less than 100 nm, the deposited film is prone to discontinuity, failing to form a complete crystalline layer with effective template function; if the thickness exceeds 500 nm, the seed layer is too thick, increasing material consumption and processing time, and potentially affecting the quality of subsequent epitaxial crystal growth due to increased accumulated stress. To further optimize performance and cost-effectiveness, the seed layer thickness is preferably 200-300 nm, which provides a sufficient crystalline template while achieving the best balance between material utilization and process efficiency. Furthermore, the coefficient of variation of the grain size of this seed layer is less than 15%, and the good size uniformity ensures a concentrated grain size distribution on the seed layer surface, thereby providing a consistent and stable nucleation interface for the uniform epitaxial growth of large cadmium telluride grains, which is beneficial for obtaining an absorption layer with uniform crystal structure and consistent photoelectric properties.

[0035] S2. The seed layer is annealed under high temperature and high pressure in a sealed container. The annealing temperature is 400~600℃, the annealing pressure is 10~30MPa, and the holding time is 0.5~3h.

[0036] Preferably, the seed layer is annealed under high temperature and high pressure in a sealed container, with an annealing temperature of 500~550℃, an annealing pressure of 20~26MPa, and a holding time of 0.5~1.5h.

[0037] Understandably, the purpose of step S2 is to generate a high-quality seed layer. Under high temperature and pressure, small grains, due to their high surface curvature, are gradually absorbed by neighboring large grains through grain boundary migration, resulting in a significant increase in grain size (lateral dimension) and a reduction and stabilization of grain boundaries. Ultimately, the crystal quality and compactness of the seed layer film are comprehensively improved. First, the reduction of grain boundaries and bulk defects significantly suppresses carrier recombination, making V oc (Open-circuit voltage) is significantly improved; secondly, the larger grain size reduces carrier scattering, improves mobility and collection efficiency, thereby increasing J sc (Short-circuit current density); furthermore, the improved material density and transport characteristics effectively reduced the series resistance, resulting in a significant increase in the fill factor (FF). These synergistic optimizations ultimately drove a significant overall increase in photoelectric conversion efficiency (PCE).

[0038] Understandably, the purpose of step S3 is to use the large-grain seed layer as a template to rapidly epitaxially grow (vertically grow) a large-grain cadmium telluride thin film layer as the absorber layer of the solar cell using a near-space sublimation method.

[0039] Understandably, in this application, S1 and S2 prepare the seed layer through a two-step method, in which cadmium telluride grains achieve lateral growth, i.e., grain size increase. S3 prepares deposited cadmium telluride to achieve longitudinal growth of the cadmium telluride grains, i.e., increase in film thickness. This method is simple, highly operable, and produces large-grained cadmium telluride with good uniformity.

[0040] In some embodiments, in S3, the deposition rate of cadmium telluride on the seed layer is 0.05~1 μm / min.

[0041] Preferably, the deposition rate of the cadmium telluride film on the seed layer is 0.1~0.5 μm / min.

[0042] Understandably, the reason why the cadmium telluride film has a deposition rate of 0.05~1μm / min on the seed layer is that at this deposition rate, the adsorbed atoms have sufficient surface migration ability, thereby suppressing problems such as amorphization, porosity or high defect density that are easily caused by high-speed deposition, and ensuring that the film maintains high orientation, high density and low defect state during rapid growth.

[0043] In some embodiments, in S1 and / or S3, the heating rate of the source and substrate is 1~100℃ / min, and the pressure increase rate is 0.1~100 Pa / min; Preferably, in S1 and / or S3, the heating rate is 50~90℃ / min and the pressure increase rate is 10~70Pa / min; In some embodiments, in step S2, the heating rate is 0.1~5℃ / min, and the pressure increase rate is 0.1~2MPa / min.

[0044] Preferably, in step S2, the heating rate is 3~5 °C / min and the pressure increase rate is 0.8~1.5 MPa / min.

[0045] In some embodiments, the methods used for depositing the seed layer in S1 and the secondary deposition of cadmium telluride in S3 are selected from at least one of near-space sublimation, vapor transport, thermal evaporation and sputtering.

[0046] Preferably, the methods used for depositing the seed layer in S1 and for the secondary deposition of cadmium telluride in S3 are selected from at least one of near-space sublimation (CSS) and thermal evaporation.

[0047] In some embodiments, the transparent substrate is selected from at least one of soda-lime glass, borosilicate glass, and flexible polymer substrate; In some embodiments, the window layer is selected from one or more combinations of metal oxides, metal nitrides, cadmium sulfide, cadmium selenide, and cadmium telluride selenide.

[0048] In order to enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to demonstrate the significant improvement in performance of the large-grain cadmium telluride thin film, its preparation method, and the cadmium telluride solar cell device containing it provided by the embodiments of this application, the above technical solutions are illustrated below through examples.

[0049] Example 1 The structure of the large-grain cadmium telluride thin-film solar cell device prepared in this embodiment is as follows: Figure 2 As shown, it sequentially includes a glass substrate layer 201, a transparent conductive film (TCO conductive layer) 202, a window layer 203, a cadmium telluride absorption layer (large grain cadmium telluride film) 204, a back contact layer 205, and a metal electrode layer (back electrode) 206.

[0050] 1. Place the commercial TCO glass substrate containing the glass substrate layer 201 and the TCO conductive layer 202 into detergent, acetone, ethanol and deionized water for ultrasonic cleaning for 15 minutes, blow it dry with nitrogen and then put it into an oven to dry.

[0051] 2. Place a clean TCO glass substrate into a coating equipment to rapidly deposit a 150nm cadmium selenide thin film as the window layer 203.

[0052] 3. The process for preparing large-grain cadmium telluride thin films in 204 is as follows: Figure 1 As shown: (1) Use nitrogen gas to blow away the attached impurities on the surface of the cadmium selenide film sample.

[0053] (2) The sample in (1) was placed in the CSS system to rapidly deposit a 300 nm cadmium telluride thin film seed layer, with a source temperature of 700 °C, a substrate heating temperature of 580 °C, an argon gas pressure of 200 Pa, and a source-to-substrate distance of 3 mm.

[0054] (3) Clean the inside and outside of the reactor, and blow away the impurities attached to the surface of the seed layer in (2) with nitrogen gas. Then place it on the sample rack inside the reactor, close the reactor, and check the sealing to ensure that there is no leakage during the annealing process, so as to prevent the annealing pressure and film quality from being affected.

[0055] (4) Slowly introduce argon gas into the reactor and gradually increase the internal pressure to 25 MPa at 1 MPa / min. At the same time, start the temperature control system to increase the temperature inside the reactor to 500℃ at 5℃ / min and maintain the temperature for annealing for 80 min.

[0056] (5) After annealing, turn off the heating and allow the reactor to cool down naturally at room temperature. After reaching room temperature, slowly release the gas and take out the sample.

[0057] (6) Transfer the sample from (5) to the CSS system for secondary epitaxial deposition of a 3.2 μm CdTe polycrystalline thin film, wherein the source temperature is 700 °C, the substrate heating temperature is 580 °C, the argon gas pressure is 200 Pa, and the distance between the source and the substrate is 3 mm.

[0058] like Figure 3 As shown, the prepared cadmium telluride grains ranged in size from 110 to 190 μm, with an average grain size of 151.1 μm and a grain size variation coefficient of 10.8%. Furthermore, XRD results showed that ( Figure 6 The prepared cadmium telluride thin film has a significant (111) crystal plane preferred orientation, which reflects its good crystallization performance.

[0059] 4. Spray a 70 g / L cadmium chloride solution evenly onto the CdTe film surface and anneal at 400°C for 30 min.

[0060] 5. Clean the surface of the CdTe thin film sample sequentially with 3% dilute nitric acid solution and deionized water.

[0061] 6. Sequentially deposit 30nm ZnTe:Cu and 200nm molybdenum as the back contact layer 205 and the back electrode 206.

[0062] 7. Anneal the deposited sample at 200℃ for 20 minutes to obtain a complete thin-film solar cell device.

[0063] Example 2 Compared to Example 1, the difference in this example is that the annealing time of the seed layer is 35 minutes, while the remaining steps are the same as in Example 1, resulting in a thin-film solar cell device.

[0064] like Figure 4 As shown, the prepared cadmium telluride grains ranged in size from 90 to 170 μm, with an average grain size of 130.1 μm and a grain size variation coefficient of 14.3%.

[0065] Example 3 Compared to Example 1, the difference in this example is that the annealing temperature of the seed layer is 400°C, while the remaining steps are the same as in Example 1, resulting in a thin-film solar cell device.

[0066] like Figure 5 As shown, the prepared cadmium telluride grains ranged in size from 80 to 140 μm, with an average grain size of 104.9 μm and a grain size variation coefficient of 13.3%.

[0067] Comparative Example 1 Compared to Example 1, the difference in this comparative example is that, in the fabrication process of the thin-film solar cell, a seed layer is not used, but a 3.2 μm cadmium telluride absorber layer is directly deposited on the cadmium selenide window layer. The remaining steps are the same as in Example 1.

[0068] Comparative Example 2 Compared to Example 1, the difference in this comparative example is that a secondary epitaxial deposition step is not performed in the fabrication process of the thin-film solar cell, while the remaining steps are the same as in Example 1.

[0069] The physical parameters of grain size, average grain size, grain size variation coefficient, and minority carrier lifetime of large-grained cadmium telluride in each embodiment and comparative example are summarized in Table 1 below.

[0070] Table 1

[0071] The performance of the large-grain cadmium telluride thin-film solar cell devices prepared in each embodiment and comparative example was tested, and the results are shown in Table 2 below.

[0072] Photoelectric performance testing: Under standard test conditions (AM 1.5G, 100 mW / cm², 25℃), the current-voltage characteristics of the device were scanned using a solar simulator. The open-circuit voltage, short-circuit current density, fill factor and photoelectric conversion efficiency were directly obtained by analyzing the obtained IV curves, thereby systematically characterizing the energy conversion performance of the device under illumination.

[0073] Minority carrier lifetime testing: Time-resolved photoluminescence method is used: the sample is excited by an ultrashort pulse laser to generate electron-hole pairs. When these non-equilibrium carriers recombine radiatively, they emit fluorescence. Since the decay of fluorescence intensity directly reflects the decay of non-equilibrium minority carrier concentration, the minority carrier lifetime can be fitted by detecting the change in fluorescence intensity over time.

[0074] Table 2

[0075] Comparing Examples 1 to 3 with Comparative Examples 1 to 2, by controlling the seed layer grain size to be 50-200 μm, the average grain size to be 95-155 μm, and the thickness to be 100-500 nm, and then using this seed layer as a template for secondary epitaxial deposition of cadmium telluride, the resulting large-grain cadmium telluride has a large grain size (lateral dimension), and the grain size variation coefficient is below 15%, indicating good size uniformity. This reduces grain boundaries and bulk defects, improves grain quality, and increases open-circuit voltage, short-circuit current density, and fill factor compared to Comparative Examples 1 and 2. Furthermore, the photoelectric conversion efficiency is also significantly improved (e.g., ...). Figure 7(As shown).

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A large-grain cadmium telluride thin film, characterized in that, The film includes cadmium telluride grains, wherein the grain size of the cadmium telluride grains is 50~200μm, the average grain size is 95~155μm, and the coefficient of variation of the grain size is less than 15%; the large-grain cadmium telluride film is prepared by high-temperature and high-pressure annealing under a pressure of 10~30MPa.

2. The large-grain cadmium telluride thin film according to claim 1, characterized in that, The thickness of the large-grain cadmium telluride film is 2~10μm, and the grains are columnar crystals.

3. The large-grain cadmium telluride thin film according to claim 1, characterized in that, The large-grain cadmium telluride has (111), (220), and (311) diffraction peaks in its X-ray diffraction pattern, wherein the diffraction intensities of the (220) and (311) peaks are 5% to 20% of the diffraction intensity of the (111) peak, respectively.

4. The large-grain cadmium telluride thin film according to claim 1, characterized in that, The minority carrier lifetime of the large-grain cadmium telluride thin film is greater than 300 ns.

5. A method for preparing a large-grain cadmium telluride thin film, characterized in that, Includes the following steps: S1. Deposit a 100~500nm cadmium telluride seed layer on the surface of the window layer with a transparent substrate, with a substrate temperature of 400~600℃, a source temperature of 600~800℃, and a pressure of 100~2000Pa. S2. The cadmium telluride seed layer is annealed under high temperature and high pressure at a temperature of 400~600℃, an annealing pressure of 10~30MPa, and a holding time of 0.5~3h. After annealing, the size of the seed layer grains is 50~200μm, the average grain size is 95~155μm, and the thickness is 100~500nm. S3. Under the conditions of substrate temperature of 400~600℃, source temperature of 600~800℃, and pressure of 100~2000Pa, secondary epitaxial deposition of cadmium telluride is carried out on the seed layer as a substrate to obtain a large-grain cadmium telluride thin film.

6. The preparation method according to claim 5, characterized in that, In S3, the cadmium telluride film grows at a rate of 0.05~1 μm / min on the seed layer.

7. The preparation method according to claim 5, characterized in that, In S1, the heating rate of the source and the substrate is 1~100℃ / min, and the pressure increase rate is 0.1~100 Pa / min; and / or In S3, the heating rate of the source and the substrate is 1~100℃ / min, and the pressure increase rate is 0.1~100 Pa / min.

8. The preparation method according to claim 5, characterized in that, In S2, the heating rate is 0.1~5℃ / min, and the pressure increase rate is 0.1~2 MPa / min.

9. The preparation method according to claim 5, characterized in that, The methods used for the seed layer deposition in S1 and the secondary epitaxial deposition of cadmium telluride in S3 are independently selected from at least one of near-space sublimation, vapor transport, thermal evaporation and sputtering.

10. The preparation method according to claim 5, characterized in that, The transparent substrate is selected from at least one of soda-lime glass, borosilicate glass, and flexible polymer substrate; And / or, The window layer is selected from one or more combinations of metal oxides, metal nitrides, cadmium sulfide, cadmium selenide, and cadmium telluride selenide.

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