A copper-zinc-tin-sulfur thin-film solar cell absorber layer and its preparation method

Abstract

This invention discloses a copper-zinc-tin-sulfur thin-film solar cell absorber layer, its preparation method, and the thin-film solar cell itself. The preparation method includes: using zinc, copper, and tin as evaporation sources, simultaneously initiating evaporation deposition; sequentially shutting off the zinc, tin, and copper evaporation sources according to a preset deposition time to form a precursor film on a substrate surface; pre-alloying the precursor film under a protective atmosphere; and performing a three-stage sulfurization annealing treatment on the pre-alloyed precursor film to obtain the copper-zinc-tin-sulfur thin-film solar cell absorber layer. This method, through gradient co-evaporation combined with pre-alloying and three-stage sulfurization, effectively improves the crystallinity and phase purity of the absorber layer, thereby increasing the cell efficiency.

Description

Technical Field

[0001] This invention relates to the field of thin-film solar cell technology, and in particular to a copper-zinc-tin-sulfur thin-film solar cell absorber layer and its preparation method, as well as a thin-film solar cell. Background Technology

[0002] Among numerous photovoltaic materials, copper-zinc-tin-sulfur (Cu2ZnSnS4, CZTS) is considered one of the most promising absorber layer materials for next-generation thin-film solar cells due to its excellent photoelectric properties, high theoretical efficiency, abundant and non-toxic constituent elements in the Earth's crust, and environmental friendliness. CZTS possesses a high light absorption coefficient, a band gap matching the solar spectrum, and its band gap can be tunable through selenium doping (CZTSSe). These characteristics give it broad application prospects in the field of thin-film photovoltaics.

[0003] The preparation methods for CZTS thin films mainly fall into two categories: solution methods and vacuum evaporation methods. Solution methods (such as sol-gel methods, hydrothermal methods, and electrodeposition methods) are relatively simple and have low equipment costs, but they require the use of large amounts of organic solvents such as hydrazine, ethylene glycol, and dimethyl sulfoxide (DMSO). These organic solvents are difficult to completely remove in subsequent processing, and residual carbon elements can enter the CZTS thin film, forming deep-level defects and carrier recombination centers, significantly affecting the open-circuit voltage and fill factor of the device. In addition, films prepared by solution methods have higher porosity and are less dense than those prepared by vacuum methods.

[0004] Vacuum evaporation methods mainly include magnetron sputtering and thermal evaporation. Magnetron sputtering offers controllable deposition rates and good film adhesion, but its target utilization is low, and high-energy particle bombardment of the substrate surface may introduce damage. Thermal evaporation has advantages such as high material utilization, simple equipment structure, and easy independent adjustment of process parameters, making it particularly suitable for the layer-by-layer preparation of multi-element compounds. Among existing thermal evaporation processes for preparing CZTS, Chinese invention patent 201410294657.3 discloses a method for improving the crystallinity of copper-zinc-tin-sulfur thin films in the absorber layer of solar cells. This patent uses a thermal evaporation process to evaporate copper-zinc-tin stacks in a Zn / Sn / Cu sequence, followed by pre-annealing and sulfidation treatment. However, the patent has the following shortcomings: First, it does not specify the metal evaporation rate, and the difference in the evaporation rate of different metals may lead to the deviation between the actual deposition thickness of each layer and the theoretical value; second, both pre-annealing and sulfidation take more than 1 hour, which is a long preparation cycle and is not conducive to improving the efficiency of industrial production; third, the sulfidation process adopts a single-step high-temperature treatment, and the reaction between sulfur and metal is not sufficient, and the surface of the film is prone to fragmented crystals and impurities.

[0005] Therefore, it is evident that there is currently a lack of a CZTS absorber layer preparation method that can simultaneously achieve high crystal quality, short preparation cycle, and good process controllability. Summary of the Invention

[0006] This invention aims to provide a method for preparing a copper-zinc-tin-sulfur (CZTS) thin-film solar cell absorber layer and a thin-film solar cell comprising the absorber layer. This addresses at least one of the problems in existing evaporation methods for preparing CZTS absorber layers: uneven element distribution, high sulfidation temperature, long sulfidation time, and poor absorber layer crystallinity.

[0007] The core inventive concept of this invention lies in employing a gradient co-evaporation strategy, using three high-purity metals—zinc (Zn), copper (Cu), and tin (Sn)—as evaporation sources. Evaporation begins simultaneously under the condition that the evaporation rate satisfies Zn > Sn > Cu, and is controlled by the evaporation time and rate. Following a preset evaporation time, the Zn, Sn, and Cu evaporation sources are sequentially stopped, forming a precursor film with an elemental concentration gradient on the substrate. Subsequently, the precursor film undergoes pre-alloying treatment under a protective atmosphere, causing the three metal elements to redistribute and become more uniform within the film layer, and allowing Cu and Sn / Zn to form Cu-Sn and Cu-Zn eutectics. Finally, a three-stage sulfurization annealing process is used. The first stage involves low-temperature semi-sulfidation to fully wet the film layer with sulfur vapor; the second stage involves medium-temperature bulk sulfurization to allow the metal elements to fully react with sulfur to generate the CZTS crystalline phase; and the third stage involves short-time high-temperature annealing to promote grain growth, resulting in a CZTS absorber layer with high phase purity and large grain size. Specifically: In a first aspect, a method for preparing an absorber layer in a copper-zinc-tin-sulfur thin-film solar cell includes the following steps: Provide substrate; Zinc, copper, and tin are used as evaporation sources and evaporation begins simultaneously. According to the preset evaporation time, the evaporation sources of metallic zinc, metallic tin and metallic copper are turned off in sequence to form a precursor film on the substrate surface; The precursor film is pre-alloyed under a protective atmosphere, and then subjected to a three-stage sulfurization annealing process to obtain the copper-zinc-tin-sulfur thin-film solar cell absorber layer.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0009] As a preferred technical solution, in the preparation method, the evaporation rate of each evaporation source satisfies the following order: zinc > tin > copper.

[0010] As a preferred technical solution, the preparation method, wherein the evaporation sources of metallic zinc, metallic tin, and metallic copper are sequentially shut off according to a preset evaporation time, specifically includes: During the vapor deposition process, the film thickness is controlled and detected using the vapor deposition time and parameters displayed by the crystal oscillator. When the zinc vapor deposition time meets the preset vapor deposition time, the zinc evaporation source is stopped. When the tin evaporation time meets the preset evaporation time, the tin evaporation source is stopped; When the copper evaporation time meets the preset evaporation time, the copper evaporation source is stopped.

[0011] As a preferred technical solution, in the preparation method, the temperature of the pre-alloying treatment is 250-350℃, the time is 10-20min, and the protective atmosphere is nitrogen or argon.

[0012] As a preferred technical solution, the preparation method includes the following three-stage vulcanization annealing treatment: a first stage of heating to 280-320℃ and holding for 10-15 minutes; a second stage of heating to 570-590℃ and holding for 10-15 minutes; and a third stage of heating to 610-630℃ and holding for 1-6 minutes.

[0013] As a preferred technical solution, in the preparation method, the three-stage sulfurization annealing treatment is carried out in a graphite box, and sulfur powder and tin sulfide are added to the graphite box. The amount of sulfur powder added is 0.2-0.5g, and the amount of tin sulfide added is 0.1-0.5g.

[0014] As a preferred technical solution, in the preparation method, the cumulative evaporation time of the zinc metal source is 100-120s, the cumulative evaporation time of the tin metal source is 265-280s, and the cumulative evaporation time of the copper metal source is 400-430s; the evaporation rate of zinc is 9-11 Å / s, the evaporation rate of copper is 2.5-3.5 Å / s, and the evaporation rate of tin is 5.5-6.5 Å / s.

[0015] As a preferred technical solution, in the preparation method, the pre-alloying treatment is carried out by natural heating on a hot table, and the time to heat from room temperature to 250°C is 8-15 minutes.

[0016] Secondly, a copper-zinc-tin-sulfur thin-film solar cell absorber layer is provided, wherein the copper-zinc-tin-sulfur thin-film solar cell absorber layer is prepared by the preparation method described above.

[0017] Thirdly, a copper-zinc-tin-sulfur thin-film solar cell includes a copper-zinc-tin-sulfur thin-film solar cell absorber layer as described above.

[0018] Beneficial effects: Compared with existing technologies, this invention employs gradient co-evaporation combined with real-time evaporation time feedback for sequential shutdown control, achieving a gradient distribution of Zn, Sn, and Cu elements in the precursor film. The Zn>Sn>Cu evaporation rate design reduces the tendency of Zn loss during high-temperature sulfidation, ensuring the stoichiometry of the final absorber layer. Pre-alloying treatment utilizes the melting characteristics of Sn to form a Cu-Sn eutectic, achieving a uniform elemental distribution. The three-stage sulfidation process decomposes the sulfidation process into three functionally distinct stages: semi-sulfidation, main sulfidation, and grain growth. The temperature and time of each stage are independently optimized, ensuring sufficient sulfidation while shortening the total sulfidation time. Furthermore, the high-temperature, short-time treatment in the third stage promotes grain growth. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the process for preparing the absorber layer of a copper-zinc-tin-sulfur thin-film solar cell according to an embodiment of the present invention.

[0021] Figure 2 This embodiment of the invention refers to the EDS collection area of ​​the thin film obtained by vapor deposition and the peak values ​​of each element collected, where a is the EDS collection area and b is the peak value of each element collected.

[0022] Figure 3 This is the EDS scanning result of the pre-alloying of the thin film obtained by vapor deposition in an embodiment of the present invention.

[0023] Figure 4 The graph shows the temperature-time curve of the three-stage vulcanization annealing process in this embodiment of the invention. The horizontal axis represents time (min) and the vertical axis represents temperature (°C). The curve passes through three stages in sequence: 300°C / 15min, 580°C / 15min and 620°C / 5min.

[0024] Figure 5 The XRD pattern of the CZTS thin film prepared in an embodiment of the present invention.

[0025] Figure 6 The image shows a cross-sectional SEM image of the CZTS thin film prepared according to an embodiment of the present invention.

[0026] Figure 7 The surface SEM image of the CZTS film prepared in an embodiment of the present invention.

[0027] Figure 8 The JV characteristic curve of the CZTS thin-film solar cell prepared for an embodiment of the present invention under standard AM1.5 illumination conditions. Detailed Implementation

[0028] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0029] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0030] like Figure 1 As shown, this embodiment of the invention provides a method for preparing the absorber layer of a copper-zinc-tin-sulfur thin-film solar cell, comprising the following steps: S101, Provide substrate; S102, Using metallic zinc, metallic copper, and metallic tin as evaporation sources, the vapor deposition process begins simultaneously; S103. According to the preset evaporation time, the evaporation sources of metallic zinc, metallic tin and metallic copper are turned off in sequence to form a precursor film on the substrate surface. S104. The precursor film is pre-alloyed under a protective atmosphere, and the pre-alloyed precursor film is subjected to a three-stage sulfurization annealing treatment to obtain the copper-zinc-tin-sulfur thin-film solar cell absorber layer.

[0031] In this embodiment, the substrate is soda-lime glass, and the precursor film is prepared by thermal evaporation, which has a higher material utilization rate compared to magnetron sputtering. Compared to solution methods, thermal evaporation does not require contact with organic solvents during the preparation process, thereby reducing the adverse effects of organic matter on battery defects. Cu, Zn, and Sn are deposited simultaneously, with all materials used having a purity of over 99.99% and existing in granular or powder form. Different evaporation rates are used for Cu, Zn, and Sn during the deposition process: Cu at 2.5-3.5 Å / s, Zn at 9-11 Å / s, and Sn at 5.5-6.5 Å / s. During the deposition process, Zn, Sn, and Cu are evaporated sequentially according to their evaporation time, and then the evaporation source is turned off.

[0032] Combination Figure 2 As shown, during the vapor deposition process, the atomic ratios were Cu / (Zn+Sn) = 0.80-0.95 and Zn / Sn = 1.15-1.25. EDS measurements of the atomic ratios of each element yielded the following results: copper 47.77 at.%, zinc 28.53 at.%, and tin 23.69 at.%. EDS analysis of the surface composition before sulfidation yielded Cu / (Zn+Sn) ≈ 0.91 and Zn / Sn ≈ 1.20.

[0033] In this embodiment, the pre-alloying treatment is carried out under a protective atmosphere (nitrogen or argon) at a temperature of 250-350℃ for 10-20 minutes. This temperature range is selected based on the melting point of Sn (approximately 232℃): when the temperature rises above 230℃, Sn begins to melt, and the molten Sn interdiffused with solid Cu to form a Cu-Sn eutectic liquid phase. The eutectic liquid phase flows and spreads within the film layer, promoting the redistribution and homogenization of Cu, Zn, and Sn within the film layer, reducing local elemental segregation caused by sequential shutdown during the vapor deposition process. Furthermore, the formation of the Cu-Sn eutectic provides a favorable chemical microenvironment for the nucleation of the CZTS crystal phase in the subsequent sulfidation stage. The pre-alloying treatment is performed using a natural heating method on a hot plate, with the temperature rising from room temperature to 250℃ in 8-15 minutes. This natural heating method avoids thermal stress cracking of the film layer caused by rapid heating.

[0034] In one implementation, pre-alloying can also be carried out in a tube furnace, using a programmed heating method to precisely control the heating rate and holding time, setting the heating rate to 10℃ / min, 15℃ / min or 20℃ / min, and the holding temperature to 275℃, 300℃ or 325℃.

[0035] To ensure better curing of the precursor film, curing is carried out in a tube furnace. The prepared precursor film is placed in a graphite box with an appropriate amount of sulfur powder added, such as 0.2-0.5g of sulfur powder and 0.1-0.5g of SnS. The purpose of using SnS to assist in curing is to compensate for the loss of Sn at high temperatures. Curing is carried out under a nitrogen or argon protective gas atmosphere, with the gas pressure controlled between 0.25-0.5 atm.

[0036] Vulcanization process flow diagram as follows Figure 4 As shown, in order to form pure-phase CZTS during the vulcanization process, the present invention adopts a three-stage vulcanization process. The first stage is heated to 300°C and held for 15 minutes to allow the precursor film to react with a small amount of S. The second stage is heated to 580°C and held for 15 minutes to allow the precursor film and S to react fully to form CZTS crystals. The third stage is heated to 620°C and held for 5 minutes to allow the CZTS crystals to form a large grain structure.

[0037] In the three-stage sulfidation process, both the first and second stages employ a heating rate of 10-20℃ / min. The first stage, holding at 300℃ for 15 minutes, is a semi-sulfidation stage, primarily aimed at sublimating sulfur (S). The second stage, holding at 580℃ for 15 minutes, allows the Cu, Sn, and Zn metals to fully react with S to form CZTS. The third stage, using a heating rate of 20℃ / min and holding at 620℃ for 5 minutes, promotes the growth of the CZTS grains and reduces grain fragmentation. The XRD pattern of the surface obtained after sulfidation is shown below. Figure 5 As shown, Figure 6 Here is a cross-sectional SEM image of the CZTS thin film. Figure 7 This is a surface SEM image of the CZTS thin film.

[0038] In one implementation, the film can be quenched after vulcanization annealing by rapid cooling (e.g., introducing a large amount of cooling gas or removing it from the high-temperature zone) to preserve the high-temperature phase structure and defect state. In another implementation, a low-temperature annealing treatment (e.g., 400℃ / 30min) can be added after vulcanization to further optimize the defect distribution of the CZTS film.

[0039] In one implementation, the temperature and time of each stage of the three-stage vulcanization can be adjusted within a certain range: the temperature of the first stage can be adjusted within the range of 280-320℃, and the holding time can be adjusted within the range of 10-15min; the temperature of the second stage can be adjusted within the range of 570-590℃, and the holding time can be adjusted within the range of 10-15min; the temperature of the third stage can be adjusted within the range of 610-630℃, and the holding time can be adjusted within the range of 1-6min.

[0040] Based on the same inventive concept, this invention also provides a copper-zinc-tin-sulfur thin-film solar cell absorber layer, which is prepared using the preparation method provided in the above embodiments.

[0041] Based on the same inventive concept, this invention provides a copper-zinc-tin-sulfur thin-film solar cell, which includes the aforementioned copper-zinc-tin-sulfur thin-film solar cell absorber layer.

[0042] The above technical solution will be further explained and illustrated through specific preparation examples below.

[0043] Example 1 Sodium-calcium glass was selected as the substrate, and its size was determined according to experimental requirements, preferably a square sheet of 25mm × 25mm. The substrate was sequentially ultrasonically cleaned for 15 minutes each in deionized water, acetone, and isopropanol to remove surface oil and particulate contaminants, and then dried with high-purity nitrogen. The cleaned and dried substrate was placed on the sample holder of the vacuum evaporation machine, with the substrate surface facing the evaporation source. To improve film adhesion, the substrate temperature was maintained at room temperature.

[0044] Metal layers were deposited using a resistance-heated vacuum evaporation machine. Zn, Cu, and Sn particles with a purity greater than 99.99% were respectively loaded into three independent molybdenum or tungsten boat evaporation sources. The chamber door was closed, and the vacuum system was activated to begin evacuation. A two-stage evacuation process, using both a mechanical pump and a molecular pump, was employed until the chamber vacuum reached 5 × 10⁻⁶. -4 Below Pa. Simultaneously, three evaporation sources—zinc, copper, and tin—were activated to begin evaporation. During the deposition process, the evaporation rate of each metal film was monitored in real time using a quartz crystal oscillator. The evaporation rate for zinc was set to 10 Å / s, for tin to 6 Å / s, and for copper to 3 Å / s. When the evaporation time for Zn reached the set value, the zinc evaporation source was turned off (cumulative evaporation time for zinc approximately 105 s); when the evaporation time for tin reached the preset value, the tin evaporation source was turned off (cumulative evaporation time for tin approximately 268 s); and when the evaporation time for copper reached the preset value, the copper evaporation source was turned off (cumulative evaporation time for copper approximately 410 s). After evaporation was complete, a precursor film with an elemental concentration gradient was formed on the substrate.

[0045] The precursor film sample prepared in the previous step was removed from the vacuum evaporation machine and transferred to a glove box for pre-alloying treatment. Pre-alloying was carried out under a nitrogen or argon protective atmosphere with a purity of 99.99% or higher, and the gas flow rate was adjusted to maintain a positive pressure environment within the glove box. The sample was placed on a hot stage, and the temperature was naturally raised from room temperature to 250°C. After reaching the target temperature, it was held for 15 minutes to allow the Zn, Cu, and Sn metal elements in the precursor film to undergo interdiffusion and alloying reactions, forming Cu-Sn, Cu-Zn eutectics, and other intermetallic compounds. After pre-alloying, the sample was naturally cooled to room temperature. This natural cooling process helps to form a stable eutectic structure and avoids stress accumulation and film cracking caused by rapid cooling.

[0046] The effects of pre-alloying on the quality of subsequent CZTS films include: blurring the interfaces between metal layers and promoting uniform element distribution; forming Cu-Sn and Cu-Zn eutectic phases, reducing the chemical activity and loss of Sn during the sulfidation process; and eliminating interlayer interface defects in advance through solid-phase diffusion, thereby reducing stress concentration and cracking risks during subsequent sulfidation annealing.

[0047] The pre-alloyed CZT precursor film sample was placed in a graphite box. The graphite box was made of high-purity graphite material, possessing excellent thermal conductivity and high-temperature resistance. Approximately 0.4g of sulfur powder and approximately 0.3g of tin sulfide (SnS) were evenly spread at the bottom of the graphite box. The purity of the sulfur powder was required to be above 99.9%, and the purity of the SnS was required to be above 99.5%. The sample was placed on top of the sulfur powder and SnS, the graphite box was closed, and the box was placed in a tube furnace.

[0048] The vulcanization annealing adopts a three-stage heating process. The specific process of the three-stage vulcanization is as follows: Stage 1: The temperature of the tube furnace is increased from room temperature to 300℃ at a heating rate of 10℃ / min, and then held at 300℃ for 15 minutes. During this stage, the sulfur powder inside the graphite box melts and evaporates, forming a sulfur vapor environment with a certain partial pressure. The gaseous sulfur in the graphite box forms a sulfur vapor environment with a certain partial pressure, comes into contact with the surface of the precursor film, and undergoes a preliminary sulfidation reaction, forming a thin CZTS sulfidation layer on the surface of the precursor film. This sulfidation layer acts as a barrier layer, helping to suppress the rapid volatilization of Sn and Zn at high temperatures and regulating the sulfidation reaction rate. Stage 2: The temperature is further increased to 580℃ at a heating rate of 15℃ / min, and then held at 580℃ for 15 minutes. At this stage temperature, the metal elements in the precursor film undergo a complete thermochemical reaction with the gaseous sulfur, and Zn, Cu, and Sn combine with S to form CZTS compounds. This temperature is the key stage for CZTS phase formation, and the main driving force of the reaction is the chemical affinity between the metal elements and sulfur. The third stage involves rapidly heating to 620℃ within 2 minutes and holding at 620℃ for 5 minutes. This stage uses a relatively high temperature and a short holding time, primarily to promote further growth of the existing CZTS grains and grain boundary fusion, rather than to further increase the amount of CZTS formed. At the higher temperature of 620℃, small grains mature, and surface fragments are absorbed by larger grains through atomic diffusion, significantly reducing the number of grain boundaries and resulting in a denser and smoother film surface. After curing, the tube furnace heating power is turned off, and the sample is allowed to cool naturally to room temperature within the furnace. This natural cooling process avoids thermal stress and film cracking introduced by rapid artificial cooling. The CZTS absorber layer film is then obtained by removing the sample.

[0049] A ZTO buffer layer is deposited on the surface of the CZTS absorber film prepared above using atomic layer deposition (ALD) or magnetron sputtering. ZTO (Zn0.05) x Sn 1-x O) is an amorphous oxide semiconductor with a band gap of about 3.3 eV, which matches the conduction band position of CZTS well. It can effectively reduce the interface barrier and interface recombination between CZTS and transparent conductive layer, and the thickness is controlled at about 50 nm.

[0050] Next, an ITO transparent conductive oxide layer with a thickness of approximately 330 nm was deposited on the surface of the ZTO buffer layer using magnetron sputtering. ITO has low resistivity (less than 5 × 10⁻⁶). -4 With its high transmittance of light (Ω·cm) and visible light, its low resistance reduces series resistance loss, while its high transmittance ensures that most incident light can pass through to reach the CZTS absorption layer.

[0051] Subsequently, Ag electrodes were deposited on the ITO surface using thermal evaporation, and patterned into grid lines using a mask to form a current collection network. Finally, an antireflective layer of approximately 100 nm thick, MgF2, was deposited using electron beam evaporation. MgF2 has a refractive index of approximately 1.38, falling between the refractive index of air (1.0) and that of ITO (approximately 2.0), reducing incident light reflection loss by about 10% at the CZTS device surface and increasing the short-circuit current density. Through the layer-by-layer deposition of these functional layers, the complete fabrication of the CZTS thin-film solar cell was achieved.

[0052] Under standard AM1.5 lighting conditions (1000W / m²) 2 The IV characteristics of the fabricated CZTS thin-film solar cells were tested using a solar simulator and a Keithley source meter at 25°C. The test results are as follows: Figure 8 As shown, the main photoelectric parameters of the battery are: efficiency reached 10.04%, open-circuit voltage reached a maximum of Voc=0.737V, and JSC=25.15mA / cm. 2 FF=54.16%.

[0053] This efficiency is among the best in CZTS thin-film solar cells prepared by thermal evaporation, demonstrating the excellent material quality and photoelectric performance of the CZTS absorber layer prepared by the method of this invention. The high short-circuit current density indicates that the CZTS absorber layer has high absorption efficiency for incident light and good carrier collection efficiency. This is attributed to the high-quality thin film with large grains and few grain boundaries obtained by the three-stage sulfidation process, reducing grain boundary recombination. The high fill factor indicates good interface quality between the CZTS absorber layer and the buffer layer, with low series resistance and high parallel resistance. The faster sulfidation rate also provides a technological basis for improving production efficiency. In terms of material utilization, thermal evaporation of CZTS offers higher material utilization than magnetron sputtering because the evaporated material is directly deposited on the substrate, eliminating the material waste caused by uneven target etching. Compared to solution methods, thermal evaporation does not involve any organic solvents, fundamentally avoiding the influence of organic carbon impurities on cell defects.

[0054] Example 2 By adjusting some of the process parameters in Example 1 above, a CZTS film with good crystallinity can also be obtained. Specifically, the evaporation rate of the Zn layer during co-deposition is set to 9 Å / s, the evaporation rate of the Cu layer is set to 3.5 Å / s, and the evaporation rate of the Sn layer is set to 5.5 Å / s; the Zn layer deposition time is adjusted to 120 s, the Sn layer deposition time is adjusted to 265 s, and the total Cu deposition time is adjusted to 420 s. The pre-alloying temperature is set to 300℃, and the holding time is 15 min. The three-stage sulfurization annealing parameters are adjusted as follows: first stage 320℃ / 12 min, second stage 570℃ / 18 min, and third stage 630℃ / 1 min. Other process conditions are the same as in Example 1.

[0055] Example 3 By adjusting some of the process parameters in Example 1 above, a CZTS film with good crystallinity can also be obtained. Specifically, the evaporation rate of the Zn layer during co-evaporation is set to 11 Å / s, the evaporation rate of the Cu layer is set to 2.5 Å / s, and the evaporation rate of the Sn layer is set to 6.5 Å / s; the evaporation time of the Zn layer is adjusted to 100 s, the evaporation time of the Sn layer is adjusted to 280 s, and the total evaporation time of Cu is adjusted to 430 s. The pre-alloying temperature is set to 350℃, and the holding time is 15 min. The three-stage sulfurization annealing parameters are adjusted as follows: first stage 280℃ / 15 min, second stage 590℃ / 10 min, and third stage 610℃ / 3 min. Other process conditions are the same as in Example 1.

[0056] It should be noted that the vapor deposition equipment (resistance heating vacuum vapor deposition machine), evaporation source (molybdenum boat, tungsten boat), protective atmosphere (nitrogen, argon), sulfurization device (tube furnace, graphite box), and specific process parameters (evaporation rate, vapor deposition time, interval time, annealing temperature, annealing time, sulfurization temperature, sulfurization time, etc.) described in the above embodiments are all specific implementations of the present invention and do not constitute a limitation on the present invention. In alternative solutions: the evaporation source can be electron beam evaporation instead of resistance heating; pre-alloying and sulfurization annealing can be carried out continuously in the same tube furnace without transferring samples to simplify the operation steps; the protective atmosphere can be a nitrogen-hydrogen mixture (such as 95% N2 + 5% H2) to improve the reducing atmosphere; the graphite box can be replaced by a corundum crucible or other high-temperature resistant inert material container; the three-stage sulfurization can be carried out in a rapid annealing furnace (RTP) or a tube furnace to more precisely control the heating and cooling rates and holding time.

[0057] Finally, it should be noted that the above embodiments are only for illustrating the present invention and not for limiting the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing an absorber layer in a copper-zinc-tin-sulfur thin-film solar cell, characterized in that, Includes the following steps: Provide substrate; Using zinc, copper, and tin as evaporation sources, the vapor deposition process begins simultaneously. According to the preset evaporation time, the evaporation sources of metallic zinc, metallic tin and metallic copper are turned off in sequence to form a precursor film on the surface of the substrate; The precursor film is pre-alloyed under a protective atmosphere, and then subjected to a three-stage sulfurization annealing process to obtain the copper-zinc-tin-sulfur thin-film solar cell absorber layer.

2. The preparation method according to claim 1, characterized in that, The evaporation rates of each evaporation source satisfy the following order: zinc > tin > copper.

3. The preparation method according to claim 2, characterized in that, According to the preset evaporation time, the evaporation sources for zinc, tin, and copper are turned off sequentially, specifically including: During the vapor deposition process, the film thickness is controlled and detected using the vapor deposition time and parameters displayed by the crystal oscillator. When the zinc vapor deposition time meets the preset vapor deposition time, the zinc evaporation source is stopped. When the tin evaporation time meets the preset evaporation time, the tin evaporation source is stopped; When the copper evaporation time meets the preset evaporation time, the copper evaporation source is stopped.

4. The preparation method according to claim 2, characterized in that, The pre-alloying treatment is carried out at a temperature of 250-350℃ for 10-20 minutes, and the protective atmosphere is nitrogen or argon.

5. The preparation method according to claim 1, characterized in that, The three-stage vulcanization annealing process includes: the first stage of heating to 280-320℃ and holding for 10-15 minutes; the second stage of heating to 570-590℃ and holding for 10-15 minutes; and the third stage of heating to 610-630℃ and holding for 1-6 minutes.

6. The preparation method according to claim 1, characterized in that, The three-stage sulfur annealing process is carried out in a graphite box containing sulfur powder and tin sulfide. The amount of sulfur powder added is 0.2-0.5g, and the amount of tin sulfide added is 0.1-0.5g.

7. The preparation method according to claim 2, characterized in that, The cumulative evaporation time for zinc metal source is 100-120 s, for tin metal source it is 265-280 s, and for copper metal source it is 400-430 s; the evaporation rate for zinc is 9-11 Å / s, for copper it is 2.5-3.5 Å / s, and for tin it is 5.5-6.5 Å / s.

8. The preparation method according to claim 1, characterized in that, The pre-alloying treatment is carried out by natural heating on a hot plate, and the time to heat from room temperature to 250°C is 8-15 minutes.

9. An absorber layer for a copper-zinc-tin-sulfur thin-film solar cell, characterized in that, The copper-zinc-tin-sulfur thin-film solar cell absorber layer is prepared using any one of the preparation methods described in claims 1-8.

10. A copper-zinc-tin-sulfur thin-film solar cell, characterized in that, Includes the copper-zinc-tin-sulfur thin-film solar cell absorber layer as described in claim 9.

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