Preparation method of tellurium-selenium-cadmium alloy film

Abstract

The invention provides a preparation method of a tellurium-selenium-cadmium alloy film, which comprises the following steps: A) mixing cadmium selenide powder and cadmium telluride powder, and performing compression molding to obtain a powder source; b) pre-oxidizing the powder source in an oxygen-containing atmosphere to obtain a pre-oxidized powder source; in the oxygen-containing atmosphere, the molar percentage of oxygen is 1-40%; and C) preparing the tellurium-selenium-cadmium alloy film from the pre-oxidized powder source through a near-space sublimation method. The preparation method solves the problem that the selenium content in the tellurium-selenium-cadmium film obtained by the preparation method of pre-oxidation is low in the past. Moreover, in the preparation process of the tellurium-selenium-cadmium alloy thin film, regulation and control of the selenium content are more accurate, controllability is higher, when the tellurium-selenium-cadmium alloy thin film is applied to large-scale production, quality stability of products is better, and the tellurium-selenium-cadmium alloy thin film is of great significance to large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a method for preparing a tellurium-cadmium-selenide alloy film. Background Art

[0002] As global carbon emissions gradually increase, countries are actively looking for ways to get rid of their dependence on traditional fossil energy. Renewable energy such as solar energy, hydropower, wind energy, biomass energy and tidal energy are playing an increasingly important role in the human energy supply system. Among them, solar cells are semiconductor devices that can directly convert sunlight into electrical energy, showing great development potential.

[0003] Cadmium telluride thin-film solar cells are different from traditional crystalline silicon solar cells in that they have the advantages of low manufacturing cost and low price. Cadmium telluride (CdTe) is a II-VI group direct bandgap semiconductor material with an optical bandgap width of 1.50 eV and an absorption coefficient of up to 10 5 cm -1 , a CdTe film of only 1~2 μm thick can absorb most of the sunlight. In recent years, the energy conversion efficiency of cadmium telluride thin film cells has made great progress, with the highest efficiency reaching 22.6%. The significant performance improvement is mainly attributed to the use of cadmium telluride selenide alloy layer in solar cells. The band gap width of the cadmium telluride selenide alloy layer is 1.38~1.42 eV, which is smaller than the band gap width of cadmium telluride 1.50 eV. Therefore, adding cadmium telluride selenide alloy film to the cadmium telluride absorption layer is conducive to enhancing the device's effective absorption of infrared photons, promoting the collection of photogenerated carriers, and enhancing the short-circuit current density parameter, thereby achieving high conversion efficiency.

[0004] Traditionally, the CdTe alloy layer in CdTe solar cells is generally formed by two methods. The traditional method is to first grow a thin CdSe layer, then grow a CdTe absorption layer, and then achieve the mutual diffusion process of selenium and tellurium through subsequent heat treatment, but this method either leads to insufficient diffusion of selenium or excessive diffusion of selenium. The content regulation and spatial distribution of selenium in the CdTe alloy layer have a huge impact on the performance of solar cells, because if the selenium content is too low, the improvement of short-circuit current is not obvious enough; if the selenium content is too high, the CdTe layer will be non-photoactive and cannot effectively collect incident photons. Another method to form a CdTe alloy layer in a solar cell is to use the near-space sublimation method to directly pre-grow a CdTe alloy film with a specific selenium content, then grow a CdTe absorption layer, and finally through appropriate heat treatment, so as to achieve effective and precise regulation of the selenium content and spatial distribution. However, since the vapor pressure of cadmium selenide is lower than that of cadmium telluride, the selenium content in the film prepared by the close-space sublimation method is much lower than the selenium content of the powder source, resulting in the inability to meet the requirements for preparing solar cells with high short-circuit current density. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a cadmium telluride selenide alloy thin film. The preparation method of the present invention can accurately control the selenium content in the cadmium telluride selenide alloy thin film within a reasonable range, and can provide technicians with sufficient adjustable space for the selenium element to improve the short-circuit current density and conversion efficiency of cadmium telluride thin film solar cells.

[0006] The present invention provides a method for preparing a tellurium-cadmium-selenide alloy thin film, comprising the following steps:

[0007] A) mixing cadmium selenide powder and cadmium telluride powder and pressing them into a shape to obtain a powder source;

[0008] B) pre-oxidizing the powder source in an oxygen-containing atmosphere to obtain a pre-oxidized powder source;

[0009] In the oxygen-containing atmosphere, the molar percentage of oxygen is 1 to 40%;

[0010] C) preparing a cadmium telluride and selenide alloy thin film by a close-space sublimation method using the pre-oxidized powder source.

[0011] Preferably, in the powder source, the molar percentage of cadmium selenide powder is 10-60%.

[0012] Preferably, the oxygen-containing atmosphere comprises oxygen and an inert gas;

[0013] During the pre-oxidation process, the total gas pressure of the oxygen-containing atmosphere is 0.5-10 kPa.

[0014] Preferably, during the pre-oxidation, the temperature of the powder source is 500-700°C.

[0015] Preferably, the pre-oxidation time is 3 to 20 minutes.

[0016] Preferably, in the step C), the pre-oxidized powder source is placed on a support plate, a substrate is placed on top, and the cadmium telluride and selenide alloy thin film is grown under a protective atmosphere.

[0017] Preferably, during the growth of the cadmium telluride and selenide alloy thin film, the temperature of the substrate is 450-600°C.

[0018] Preferably, during the growth of the cadmium telluride and selenide alloy thin film, the temperature of the pre-oxidized powder source is 550-700°C.

[0019] Preferably, the time for growing the cadmium telluride and selenide alloy film is 50 to 500 seconds.

[0020] Preferably, the protective atmosphere comprises argon and / or nitrogen;

[0021] The gas pressure of the protective atmosphere is 0.5-20 kPa.

[0022] The present invention provides a method for preparing a cadmium telluride and selenide alloy film, comprising the following steps: A) mixing cadmium selenide powder and cadmium telluride powder and pressing and molding to obtain a powder source; B) pre-oxidizing the powder source in an oxygen-containing atmosphere to obtain a pre-oxidized powder source; in the oxygen-containing atmosphere, the molar percentage of oxygen is 1-40%; C) preparing a cadmium telluride and selenide alloy film by a close-space sublimation method using the pre-oxidized powder source. The present invention pre-oxidizes the powder source so that oxides related to tellurium and selenium are generated on the surface of the source. The oxides related to selenium are conducive to the sublimation of selenium atoms and promote the transfer of selenium atoms from the surface of the powder source to the substrate, thereby solving the problem of low selenium content in the cadmium telluride and selenium films obtained by the previous preparation method without pre-oxidation. Moreover, by controlling the molar percentage of oxygen introduced during the pre-oxidation process, the oxygen content on the surface of the powder source is regulated, and the oxygen element exists in the form of oxides related to tellurium and selenium, and its state is relatively stable. This makes the regulation of selenium content in the process of preparing tellurium-selenium cadmium alloy film in the present invention more precise and controllable, and the quality stability of the product is better when applied to large-scale production, which is of great significance for realizing large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 It is a schematic flow chart of the method for preparing the cadmium telluride and selenide alloy thin film in the present invention;

[0025] Figure 2 The graph is a relationship curve between the molar percentage of oxygen and the selenium content in Examples 1, 3, 4 and 5 of the present invention;

[0026] Figure 3 1 is the XRD diagram of the cadmium telluride and selenide thin film in Example 1 of the present invention and Comparative Example 2;

[0027] Figure 4 The voltage-current density curves of the cadmium telluride solar cells using the cadmium telluride selenide thin films in Example 1 of the present invention and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing a tellurium-selenium cadmium alloy thin film, comprising the following steps:

[0029] A) mixing cadmium selenide powder and cadmium telluride powder and pressing them into a shape to obtain a powder source;

[0030] B) pre-oxidizing the powder source in an oxygen-containing atmosphere to obtain a pre-oxidized powder source;

[0031] In the oxygen-containing atmosphere, the molar percentage of oxygen is 1 to 40%;

[0032] C) preparing a cadmium telluride and selenide alloy thin film by a close-space sublimation method using the pre-oxidized powder source.

[0033] The present invention firstly mixes cadmium selenide powder and cadmium telluride powder sufficiently and evenly to obtain mixed powder, and then presses the mixed powder into a flat and dense block. The sufficient mixing of the powders and the pressing into a flat and dense block are beneficial to the uniformity of the composition and grain morphology of the subsequently prepared cadmium telluride selenide film.

[0034] In the present invention, the molar percentage of cadmium selenide powder in the mixed powder is preferably 10-60%, more preferably 20-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, preferably a range value with the above any numerical value as the upper or lower limit, and accordingly, the molar percentage of cadmium telluride powder in the mixed powder is preferably 40-90%, more preferably 50-80%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, preferably a range value with the above any numerical value as the upper or lower limit.

[0035] After obtaining the powder source, the present invention performs a pre-oxidation treatment on the powder source. Specifically, the powder source is placed in a cavity filled with an oxygen-containing atmosphere and heated at a high temperature. The corresponding oxides of tellurium and selenium are generated on the surface of the powder source, wherein the oxide related to selenium is beneficial to the sublimation of selenium atoms and promotes the transfer of selenium atoms from the surface of the powder source to the substrate, thereby solving the problem of low selenium content in the cadmium telluride and selenium thin film obtained by the previous preparation method without pre-oxidation.

[0036] In the present invention, the oxygen-containing atmosphere preferably includes oxygen and an inert gas, the inert gas is preferably nitrogen and / or argon, and the molar percentage of oxygen in the oxygen-containing atmosphere is preferably 1-40%, more preferably 10-30%, such as 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, preferably a range value with any of the above values ​​as the upper or lower limit. The greater the degree of oxidation of the mixed powder source, the higher the content of selenium in the grown cadmium telluride selenide alloy film. Therefore, by adjusting the percentage of oxygen in the pre-oxidation treatment step, technicians can regulate the selenium content in the cadmium telluride selenide alloy film.

[0037] During the pre-oxidation treatment, the total gas pressure of the oxygen-containing atmosphere in the chamber is preferably 0.5~10 kPa, preferably 1~8 kPa, such as 0.5 kPa, 1 kPa, 1.5 kPa, 2 kPa, 2.5 kPa, 3 kPa, 3.5 kPa, 4 kPa, 4.5 kPa, 5 kPa, 5.5 kPa, 6 kPa, 6.5 kPa, 7 kPa, 7.5 kPa, 8 kPa, 8.5 kPa, 9 kPa, 9.5 kPa, 10 kPa, preferably a range value with any of the above values ​​as the upper or lower limit.

[0038] In the present invention, during the pre-oxidation treatment, the temperature of the powder source is preferably 500-700°C, more preferably 550-650°C, such as 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, preferably a range value with any of the above values ​​as the upper or lower limit; the time of the pre-oxidation treatment is preferably 3-20 min, more preferably 5-15 min.

[0039] After the pre-oxidation treatment is completed, the present invention adopts a close-space sublimation method to prepare a tellurium-cadmium-selenide alloy film using a pre-oxidized powder source. Specifically, the substrate is placed in a close-space sublimation method device, a supporting plate supporting the pre-oxidized powder source is placed underneath, and a protective atmosphere is introduced to grow the tellurium-cadmium-selenide alloy film.

[0040] The near-space sublimation method used in the present invention to form a cadmium telluride and selenide alloy has the following advantages: 1. The growth rate is fast. The time required for preparing the cadmium telluride and selenide alloy layer of the cadmium telluride thin film battery is about 50 to 200 seconds; 2. The prepared cadmium telluride and selenide thin film has a larger grain size. Compared with the traditional interdiffusion method, that is, first preparing a layer of cadmium selenide and then preparing a layer of cadmium telluride on top of it, the grain size formed by this traditional method is smaller, resulting in a large number of grain boundaries, which is easy to cause the recombination of photogenerated carriers and loss of device performance; 3. The diffusion of selenium elements can be effectively controlled, because the cadmium telluride and selenide layer grown by the near-space sublimation method is not as intense as the above-mentioned traditional interdiffusion method. Therefore, the near-space sublimation method for preparing the cadmium telluride and selenide layer can provide technicians with sufficient controllable space for selenium elements.

[0041] In the present invention, the protective atmosphere is preferably nitrogen and / or argon, more preferably pure argon. The pressure of the protective atmosphere during the growth of the cadmium telluride and selenide alloy film is preferably 0.5~20 kPa, more preferably 1~15 kPa, such as 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, 11 kPa, 12 kPa, 13 kPa, 14 kPa, 15 kPa, 16 kPa, 17 kPa, 18 kPa, 19 kPa, 20 kPa, preferably a range value with any of the above values ​​as the upper or lower limit.

[0042] In the present invention, the substrate is preferably a clean glass substrate, and the temperature of the substrate is preferably 450-600°C, more preferably 500-550°C, such as 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, preferably a range value with any of the above values ​​as the upper or lower limit.

[0043] In the present invention, during the growth of the cadmium telluride and selenide alloy film, the temperature of the pre-oxidized powder source is preferably 550~700°C, more preferably 600~650°C, such as 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, preferably a range value with any of the above values ​​as the upper or lower limit; the growth time of the cadmium telluride and selenide alloy film is preferably 50~500s, more preferably 100~300s, such as 50s, 100s, 150s, 200s, 300s, 400s, 500s, preferably a range value with any of the above values ​​as the upper or lower limit; the thickness of the cadmium telluride and selenide alloy film can be controlled to be between 100~1000nm by controlling the growth time.

[0044] In the present invention, after the growth of a cadmium telluride and selenide alloy thin film is completed once, the pre-oxidized powder source does not need to be oxidized again and can be reused.

[0045] Generally speaking, the molar percentage of selenium in the cadmium telluride selenide layer in the cadmium telluride thin-film solar cell with a higher short-circuit current density, that is, the molar percentage of selenium / (selenium + tellurium) is 15-25%. The corresponding optimal band gap within this ratio range is 1.38-1.42 eV, which is smaller than the band gap of cadmium telluride, 1.50 eV. Therefore, adding a cadmium telluride selenide alloy film with the above ratio range to the cadmium telluride absorption layer is beneficial to enhancing the effective absorption of infrared photons by the device, promoting the collection of photogenerated carriers, and enhancing the short-circuit current density parameter, thereby achieving high conversion efficiency. The preparation method of the present invention can accurately control the molar percentage of selenium in the cadmium telluride selenide layer within the above range, and has good controllability and high accuracy. The preparation method of the cadmium telluride and selenide alloy thin film proposed in the present application can effectively control the selenium content in the cadmium telluride and selenide alloy thin film. Furthermore, it can effectively control the content and spatial distribution of the selenium element in the absorption layer of the cadmium telluride thin film solar cell, which is beneficial to optimize the device's full absorption of photogenerated carriers, and ultimately improve the short-circuit current density and conversion efficiency of the cadmium telluride thin film solar cell.

[0046] In order to further illustrate the present invention, a method for preparing a cadmium telluride and selenide alloy thin film provided by the present invention is described in detail below in conjunction with examples, but it should not be construed as limiting the protection scope of the present invention.

[0047] Example 1

[0048] S1, cadmium selenide powder and cadmium telluride powder are fully mixed and pressed into shape. Cadmium selenide and cadmium telluride powders are weighed using a calibrated electronic scale, and the molar ratio is: cadmium selenide: cadmium telluride = 2:3, that is, the molar percentage of cadmium selenide powder in the mixed powder is 40%. The two powders are fully mixed using a powder mixer. The mixed powder is pressed into shape using a tablet press, and the size of the pressed powder source is 60×30 mm and the thickness is 2 mm.

[0049] S2, pre-oxidize the powder source. Place the sample in a near-space sublimation device, with a graphite plate supporting the powder source underneath. Introduce a mixed gas of oxygen and argon into the chamber, where the molar percentage of oxygen in the mixed gas is 20%, and the total gas pressure is 2 kPa. Set the source temperature to 650°C and the heating time to 10 minutes.

[0050] S3, preparation of tellurium-cadmium-selenide alloy film. The tellurium-cadmium-selenide alloy film was prepared by close-space sublimation method. A clean glass substrate was placed in a close-space sublimation method device, with a graphite plate supporting the powder source underneath, and the distance between the sample surface and the powder source was 3 mm. Pure argon gas was introduced into the cavity, and the gas pressure was controlled to be 2 kPa. During the preparation process, the substrate temperature was pre-set to 500°C, the source temperature was 650°C, the growth was 150 seconds, and the thickness of the prepared cadmium-tellurium-selenide was about 500 nanometers.

[0051] According to energy spectrum testing methods such as EDS, the molar percentage of selenium in the prepared cadmium telluride selenide alloy film is 28%.

[0052] Example 2

[0053] The difference from Example 1 is that the molar percentage of cadmium selenide powder in the mixed powder of S1 is 20%. The specific description of S1 is as follows:

[0054] S1, cadmium selenide powder and cadmium telluride powder are fully mixed and pressed into shape. Cadmium selenide and cadmium telluride powders are weighed using a calibrated electronic scale, and the molar ratio is: cadmium selenide: cadmium telluride = 1:4, that is, the molar percentage of cadmium selenide powder in the mixed powder is 20%. The two powders are fully mixed using a powder mixer. The mixed powder is pressed into shape using a tablet press, and the size of the pressed powder source is 60×30 mm and the thickness is 2 mm.

[0055] The remaining steps S2 and S3 are consistent with the operation flow in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is 15%.

[0056] Example 3

[0057] The difference from Example 1 is that a mixed gas of oxygen and argon is introduced into S2 during the pre-oxidation process, wherein the molar percentage of oxygen in the mixed gas is 10%. The specific description of S2 is as follows:

[0058] S2, pre-oxidize the powder source. Place the sample in a near-space sublimation device, with a graphite plate supporting the powder source underneath. Introduce a mixed gas of oxygen and argon into the chamber, where the molar percentage of oxygen in the mixed gas is 10%, and the total gas pressure is 2 kPa. Set the source temperature to 650°C and the heating time to 10 minutes.

[0059] The remaining steps S1 and S3 are consistent with the operation flow in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is 19%.

[0060] Example 4

[0061] The difference from Example 1 is that a mixed gas of oxygen and argon is introduced into S2 during the pre-oxidation process, wherein the molar percentage of oxygen in the mixed gas is 30%. The specific description of S2 is as follows:

[0062] S2, pre-oxidize the powder source. Place the sample in a near-space sublimation device, with a graphite plate supporting the powder source underneath. Introduce a mixed gas of oxygen and argon into the chamber, where the molar percentage of oxygen in the mixed gas is 10%, and the total gas pressure is 2 kPa. Set the source temperature to 650°C and the heating time to 10 minutes.

[0063] The remaining steps S1 and S3 are consistent with the operation flow in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is 33%.

[0064] Example 5

[0065] The difference from Example 1 is that a mixed gas of oxygen and argon is introduced into S2 during the pre-oxidation process, wherein the molar percentage of oxygen in the mixed gas is 40%. The specific description of S2 is as follows:

[0066] S2, pre-oxidize the powder source. Place the sample in a near-space sublimation device, with a graphite plate supporting the powder source underneath. Introduce a mixed gas of oxygen and argon into the chamber, where the molar percentage of oxygen in the mixed gas is 40%, and the total gas pressure is 2 kPa. Set the source temperature to 650°C and the heating time to 10 minutes.

[0067] The remaining steps S1 and S3 are consistent with the operation flow in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is 35%.

[0068] Example 6

[0069] The difference from Example 1 is that the temperature of the powder source during the preparation of the S3 cadmium telluride selenide alloy film is 600° C. The specific description of S3 is as follows:

[0070] S3, preparation of tellurium-cadmium-selenide alloy film. The tellurium-cadmium-selenide alloy film was prepared by close-space sublimation method. A clean glass substrate was placed in a close-space sublimation method device, with a graphite plate supporting the powder source underneath, and the distance between the sample surface and the powder source was 3 mm. Pure argon gas was introduced into the cavity, and the gas pressure was controlled to be 2 kPa. During the preparation process, the substrate temperature was pre-set to 500°C, the source temperature was 600°C, and the growth was 150 seconds. The thickness of the prepared cadmium-tellurium-selenide was about 500 nanometers.

[0071] The remaining steps S1 and S2 are consistent with the operation process in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is 26%.

[0072] Example 7

[0073] The difference from Example 1 is that the total gas pressure of the mixed gas during the preparation of the S3 tellurium-cadmium-selenide alloy film is 5 kPa. The specific description of S3 is as follows:

[0074] S3, preparation of cadmium telluride and selenide alloy film. The cadmium telluride and selenide alloy film is prepared by close-space sublimation method. A clean glass substrate is placed in a close-space sublimation method device, with a graphite plate supporting the powder source below it, and the distance between the sample surface and the powder source is 3 mm. Pure argon gas is introduced into the cavity, and the gas pressure is controlled to be 5 kPa. During the preparation process, the substrate temperature is pre-set to 500°C and the source temperature is pre-set to 650°C. The thickness of the cadmium telluride and selenide layer is controlled to be 100~1000 nanometers by controlling the growth time. For example, if the growth time is 150 seconds, the thickness of the prepared cadmium telluride and selenide is about 500 nanometers.

[0075] The remaining steps S1 and S2 are consistent with the operation flow in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is 24%.

[0076] Comparative Example 1

[0077] The difference from Example 1 is that in S2, the powder source containing cadmium selenide and cadmium telluride powder is not pre-oxidized, that is, only pure argon gas is introduced in this process. The specific description of S2 is as follows:

[0078] S2, do not pre-oxidize the powder source. Place the above sample in a near-space sublimation device, with a graphite plate supporting the powder source below. Introduce pure argon into the chamber, that is, the molar percentage of oxygen in the mixed gas is 0, and the total gas pressure is 2 kPa. Set the source temperature to 650°C and the heating time to 10 minutes.

[0079] The remaining steps S1 and S3 are consistent with the operation flow in Example 1. In this comparative example, the powder source is not pre-oxidized, so the selenium element is not easily transferred from the powder source to the glass substrate, and the molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is only 2%.

[0080] Comparative Example 2

[0081] The difference from Example 1 is that the powder source is not subjected to the pre-oxidation process of step S2, and a mixed gas of oxygen and argon is introduced during the preparation of the tellurium-cadmium-selenide alloy film in step S3, wherein the molar percentage of oxygen in the mixed gas is 5%. The specific description of step S3 is as follows:

[0082] S3, preparation of tellurium-cadmium-selenide alloy film. The tellurium-cadmium-selenide alloy film was prepared by close-space sublimation method. A clean glass substrate was placed in a close-space sublimation method device, with a graphite plate supporting the powder source underneath, and the distance between the sample surface and the powder source was 3 mm. A mixed gas of oxygen and argon was introduced into the cavity, wherein the molar percentage of oxygen in the mixed gas was 5%, and the total gas pressure was 2 kPa. During the preparation process, the substrate temperature was pre-set to 500°C, the source temperature was 650°C, the growth was 150 seconds, and the thickness of the prepared cadmium-tellurium-selenide was about 500 nanometers.

[0083] The remaining steps S1 are consistent with the operation process in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is as high as 57%. Figure 3 and Figure 4 As shown, the film exhibits a hexagonal phase structure and is non-photoactive, resulting in an energy conversion efficiency of the solar cell of only 7.8%.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that the powder source is not subjected to the pre-oxidation process of step S2, and a mixed gas of oxygen and argon is introduced during the preparation of the tellurium-cadmium-selenide alloy film in step S3, wherein the molar percentage of oxygen in the mixed gas is 1%. The specific description of step S3 is as follows:

[0086] S3, preparation of tellurium-cadmium-selenide alloy film. The tellurium-cadmium-selenide alloy film was prepared by close-space sublimation method. A clean glass substrate was placed in a close-space sublimation method device, with a graphite plate supporting the powder source underneath, and the distance between the sample surface and the powder source was 3 mm. A mixed gas of oxygen and argon was introduced into the cavity, wherein the molar percentage of oxygen in the mixed gas was 1%, and the total gas pressure was 2 kPa. During the preparation process, the substrate temperature was pre-set to 500°C, the source temperature was 650°C, the growth was 150 seconds, and the thickness of the prepared cadmium-tellurium-selenide was about 500 nanometers.

[0087] The remaining steps S1 are consistent with the operation flow in Example 1. The molar percentage of selenium in the finally prepared cadmium telluride selenide alloy film is as high as 49%, resulting in an energy conversion efficiency of the solar cell of only 9.3%.

[0088] According to Example 1 and Comparative Examples 1 to 3, it can be seen that in Comparative Example 1, the powder source was not pre-oxidized, and oxygen was not introduced during the film growth process. The selenium content in the prepared cadmium telluride selenide film was very low, only about 2%. Figure 2 As shown, the corresponding band gap is about 1.50 eV, which cannot meet the requirements for preparing cadmium telluride thin film solar cells with high short-circuit current density. This is because the saturated vapor pressure of cadmium selenide is lower than that of cadmium telluride, resulting in the selenium content in the prepared film being much lower than the selenium content in the powder source, which makes it impossible to meet the requirements for preparing solar cells with high short-circuit current density.

[0089] Comparative Examples 2 and 3 directly use powder sources without pre-oxidation treatment to prepare CdTe thin films in an oxygen atmosphere. Even with a very low oxygen content (1%), the selenium content in the film is still relatively high, reaching 49%. The high selenium content causes the film to form a hexagonal lattice structure (such as Figure 3 As shown in Figure 2, the hexagonal CdTe thin film is non-photoactive, that is, it cannot effectively convert sunlight into photogenerated carriers, resulting in a significant reduction in the short-circuit current and conversion efficiency of the solar cell, as shown in Figure 2. Figure 4 shown.

[0090] The preparation method in Example 1 of the present invention finally prepares a cadmium telluride selenide thin film with a molar percentage of selenium of about 12-35%, which is a more suitable concentration for cadmium telluride solar cells, and the film presents a cubic lattice structure, which is photoactive in solar cells. It can be seen that the preparation method of the cadmium telluride selenide alloy thin film provided in the embodiment of the present application has a simple process, a fast film growth rate, and a controllable percentage of selenium in the prepared cadmium telluride selenide alloy thin film, which is conducive to the manufacture of a cadmium telluride thin film solar cell with higher photogenerated carrier collection efficiency and higher short-circuit circuit density.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a tellurium-cadmium-selenide alloy thin film, comprising the following steps: A) mixing cadmium selenide powder and cadmium telluride powder and pressing them into a shape to obtain a powder source; B) pre-oxidizing the powder source in an oxygen-containing atmosphere to obtain a pre-oxidized powder source; In the oxygen-containing atmosphere, the molar percentage of oxygen is 1 to 40%; C) preparing a cadmium telluride and selenide alloy thin film by a close-space sublimation method using the pre-oxidized powder source.

2. The preparation method according to claim 1, characterized in that: In the powder source, the molar percentage of cadmium selenide powder is 10-60%.

3. The preparation method according to claim 1, characterized in that: The oxygen-containing atmosphere includes oxygen and an inert gas; During the pre-oxidation process, the total gas pressure of the oxygen-containing atmosphere is 0.5-10 kPa.

4. The preparation method according to claim 1, characterized in that: During the pre-oxidation, the temperature of the powder source is 500-700°C.

5. The preparation method according to claim 4, characterized in that: The pre-oxidation time is 3 to 20 minutes.

6. The preparation method according to claim 1, characterized in that: In the step C), the pre-oxidized powder source is placed on a support plate, a substrate is placed on top, and a cadmium telluride and selenide alloy thin film is grown under a protective atmosphere.

7. The preparation method according to claim 6, characterized in that: During the growth of the cadmium telluride and selenide alloy film, the temperature of the substrate is 450-600°C.

8. The preparation method according to claim 6, characterized in that: In the process of growing the cadmium telluride and selenide alloy film, the temperature of the pre-oxidized powder source is 550-700°C.

9. The preparation method according to claim 6, characterized in that: The time for growing the cadmium telluride and selenide alloy film is 50 to 500 seconds.

10. The preparation method according to claim 6, characterized in that: The protective atmosphere comprises argon and / or nitrogen; The gas pressure of the protective atmosphere is 0.5-20 kPa.

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