Yttrium-doped cadmium sulfide thin film, preparation method and application thereof

Abstract

The application belongs to the technical field of photoelectric materials, and particularly relates to a yttrium-doped CdS thin film and a preparation method and application thereof. The preparation method of the yttrium-doped CdS thin film comprises the following steps: adding a cadmium salt solution, ammonia water and a thiourea solution into water in sequence and stirring uniformly to obtain a mixed solution; immersing a conductive substrate on which a P-type chalcogenide compound absorption layer thin film is formed into the mixed solution, and performing initial deposition through water bath heating; taking out the conductive substrate after the initial deposition, immersing it into a yttrium salt solution first, and then depositing it in the mixed solution, repeating the immersing and depositing operations for 4-6 times, and washing and drying to obtain the yttrium-doped CdS thin film. The yttrium-doped CdS thin film prepared by the application is used as a buffer layer for a CZTSSe solar cell, and a photoelectric conversion efficiency of 15.19% is achieved.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic materials technology, specifically relating to a yttrium-doped CdS thin film, its preparation method, and its application. Background Technology

[0002] Copper-zinc-tin-sulfur-selenium (CZTSSe) solar cells, as a next-generation thin-film photovoltaic technology, are considered a key candidate for achieving a low-carbon energy transition due to their abundant constituent elements, environmental friendliness, and high theoretical photoelectric conversion efficiency (over 30%). However, their highest certified efficiency is currently only 16.6%, far lower than the 23.6% of similar technologies such as copper indium gallium selenide (CIGS) cells. The main reason for this is their relatively high open-circuit voltage loss (VL). OC-deficit The core bottleneck is carrier recombination at the heterojunction interface. This heterojunction is typically composed of a p-type CZTSSe absorber layer and an n-type CdS buffer layer.

[0003] Currently, CdS buffer layers are mainly prepared by chemical bath deposition (CBD). Although this method is simple and low-cost, it has the following three inherent defects: (1) Insufficient carrier concentration: The carrier concentration of traditional CBD-CdS is usually only 10 18 cm -3 The magnitude of the charge leads to a weak built-in electric field and a wide space charge region in the heterojunction, resulting in low photogenerated carrier separation efficiency. Unseparated carriers recombine at the interface via the Shockley-Read-Hall pathway, causing severe Vo degradation. OC Loss. (2) Band mismatch: An ideal heterojunction requires a “peak-shaped” conduction band offset (CBO) between CdS and CZTSSe, with a value in the range of 0-0.4 eV, to facilitate electron extraction and block hole backflow. However, due to the uneven crystal quality of CBD-CdS, the position of its conduction band bottom (CBM) fluctuates greatly, and the actual CBO is often in the range of 0.4-0.5 eV, forming a significant electron transport barrier and hindering carrier collection. (3) Secondary phase and interface defects: In the CBD process, Cd 2+ It readily reacts with OH- in the solution - The reaction produces a Cd(OH)₂ intermediate, which readily transforms into the insulating phase CdO during subsequent processing or exposure to air. These secondary phases not only act as recombination centers themselves but also lead to the creation of cadmium vacancies (V0) in CdS. Cd Deep-level acceptor defects, such as those found in the deep-level array, further exacerbate nonradiative recombination.

[0004] To address the above problems, existing technologies mainly attempt two types of strategies: one is to use AI. 3+ In 3+ B 3+One approach is to dope CdS with cations to increase carrier concentration; another is to develop alternative buffer layer materials such as Zn(O,S) and ZnMgO to optimize band alignment. However, these strategies all have significant limitations: while cation doping can increase carrier concentration, the small radius of the doped ions (such as Al) limits its effectiveness. 3+ 0.54 Å, In 3+ The 0.80 Å concentration causes CdS lattice shrinkage, which in turn causes CBM to shift upward and CBO to increase, and cannot suppress the formation of secondary phases; while alternative materials are often complex to process and have poor compatibility with the absorption layer interface, making them difficult to apply on a large scale.

[0005] Therefore, there is currently no technology that can simultaneously and synergistically solve the three mutually coupled interface problems of "low carrier concentration, band mismatch, and multiple secondary phases". Summary of the Invention

[0006] The primary objective of this invention is to provide a method for preparing yttrium-doped CdS thin films. The preparation process is simple and compatible with existing chemical bath deposition processes. By using a cyclic "immersion + deposition" doping method, efficient and uniform doping of Y into CdS can be achieved.

[0007] A second objective of this invention is to provide a yttrium-doped CdS thin film prepared using the above-described preparation method.

[0008] A third objective of this invention is to provide an application of the aforementioned yttrium-doped CdS thin film, which is used as a buffer layer in chalcogenide thin-film batteries to significantly improve battery performance.

[0009] The fourth objective of this invention is to provide a chalcogenide thin-film battery.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a yttrium-doped CdS thin film includes the following steps: (1) Add cadmium salt solution, ammonia water and thiourea solution to water in sequence and stir until homogeneous; immerse the conductive substrate with the P-type chalcogenide absorber layer film formed in the mixed solution and perform initial deposition by water bath heating; (2) Take out the conductive substrate after initial deposition in step (1), soak it in yttrium salt solution, and then deposit it in the mixed solution. Repeat the soaking and deposition operations 4-6. After washing and drying, yttrium-doped CdS film is obtained.

[0011] The process flow diagram of this invention is as follows: Figure 1 As shown in the diagram, the reaction principle is as follows: Figure 2 As shown. By Figure 1It can be seen that in the initial deposition stage, the conductive substrate with the P-type chalcogenide absorber layer turns a blood-red color due to the deposition reaction of CdS. With repeated "immersion + deposition" cycles, a uniform yttrium-doped CdS film is eventually formed. However, in the initial deposition stage, not only is CdS deposited on the substrate surface, but Cd(OH)₂ is also generated. The specific chemical reaction principles involved are as follows... Figure 2 (a) As shown in Path 1, the present invention uses Y doping to competitively suppress the formation of insulating secondary phases such as Cd(OH)2 and CdO. After the initially deposited conductive substrate is transferred to a yttrium salt solution for immersion, Y... 3+ Adsorbed on the surface or shallow layer of CdS, some of it enters the crystal lattice through ion exchange to replace Cd. 2+ Site, forming Y Cd Donor defects provide free electrons; Y 3+ With OH in the solution - It possesses extremely strong coordination ability (YO bond formation energy is extremely low), preferentially forming YO or Y-OH complexes, thereby thermodynamically and kinetically inhibiting Cd. 2+ With OH - The reaction produces Cd(OH)2, and the specific reaction process involved is as follows: Figure 2 (a) As shown in path two; in addition, Y adsorbed on the surface 3 + Its empty 4f orbital can accept the lone pair of electrons from the sulfur atom in thiourea, forming [Y 3+ The intermediate complex [←S=C(NH2)2] lowers the energy barrier for thiourea decomposition (calculations show a decrease from 4.40 eV to -0.42 eV), accelerating the decomposition of S. 2− The release of [the substance] further promotes CdS deposition and inhibits competing side reactions. The specific chemical reaction principles involved are as follows: Figure 2 As shown in (b), the structural schematic diagram of the CdS and yttrium-doped CdS (YCdS) of the present invention is shown below. Figure 2 As shown in (c) and (d).

[0012] Further, the yttrium salt solution mentioned in step (2) is any one of yttrium nitrate solution, yttrium chloride solution, or yttrium sulfate solution; the concentration of yttrium ions in the yttrium salt solution is 0.02-0.06 mol / L. When the concentration of the yttrium salt solution is below 0.02 mol / L, the deposition effect is not significant; above 0.06 mol / L, it easily leads to Y... 3+ Excessive adsorption on the substrate surface can even lead to precipitation.

[0013] Furthermore, the soaking temperature in step (2) is 65-75 ℃, and the soaking time is 30-90 s, preferably 55-65 s. If the soaking time is too short, the Y element will not be fully doped; if the soaking time is too long, the CdS layer may dissolve slightly.

[0014] Furthermore, the deposition temperature in step (2) is 65-75 °C, and the time is 30-90 s, preferably 55-65 s. At this temperature, the reaction rate is moderate, and the film has good density.

[0015] Furthermore, the initial deposition temperature in step (1) is 65-75 °C, and the time is 5-7 min. Within this time range, it can be ensured that a continuous and complete initial CdS layer is formed as a doped substrate.

[0016] Further, in step (1), the concentration of the cadmium salt solution is 0.005-0.03 mol / L, the concentration of the thiourea solution is 0.5-2.0 mol / L, and the mass fraction of the ammonia water is 25-28%; the volume ratio of the cadmium salt solution, thiourea solution, ammonia water, and water is 1:(0.5-1):(1.2-1.5):(7-8). This dosage ratio is beneficial for CdS deposition.

[0017] Further, the P-type chalcogenide absorber film mentioned in step (1) is any one of copper zinc tin sulfur selenide (CZTSSe), copper zinc tin selenide (CZTSe), copper indium gallium selenide (CIGS), or antimony selenide (Sb2Se3).

[0018] A yttrium-doped CdS thin film is prepared by the above-described preparation method.

[0019] One application of the above-mentioned yttrium-doped CdS thin film is to use the yttrium-doped CdS thin film as a buffer layer in a chalcogenide thin-film battery.

[0020] A chalcogenide thin-film battery includes a p-type chalcogenide absorber layer and a buffer layer. The buffer layer is disposed between the p-type chalcogenide absorber layer and a transparent conductive layer, and forms a heterojunction with the p-type chalcogenide absorber layer. The buffer layer is a yttrium-doped CdS thin film as described above. The p-type chalcogenide absorber layer is any one of copper zinc tin sulfide selenide, copper indium gallium selenide, copper zinc tin selenide, or antimony selenide.

[0021] The beneficial technical effects of this invention are as follows: 1. This invention provides a method for preparing yttrium-doped CdS thin films. The preparation process is simple and controllable, employing a cyclic "immersion + deposition" doping method compatible with existing chemical bath deposition processes to achieve efficient and uniform Y doping in CdS. This invention achieves efficient and uniform Y doping into CdS by doping Y... 3+ Ions solved three core problems of CdS buffer layers: utilizing Y 3+ The extremely high oxygen affinity fundamentally inhibits the formation of insulating secondary phases such as Cd(OH)2 and CdO, reducing the interface defect state density; the formed Y CdDonor defects can provide a large number of free electrons, increasing the n-type carrier concentration of CdS films and significantly enhancing the built-in electric field and carrier separation driving force of heterojunctions. Y doping also causes the CdS Fermi level to shift upward and the conduction band bottom to shift slightly downward, optimizing the electronic band structure, reducing the conduction band offset (CBO) between it and the absorption layer, forming a "peak-shaped" band arrangement close to the theoretical optimum, and significantly reducing the electron extraction barrier.

[0022] 2. The core of this invention, the cyclic "immersion + deposition" process, does not require complex and expensive vacuum or high-temperature and high-pressure equipment. It only requires inserting a simple immersion step into the conventional chemical bath deposition step, making it easy to integrate with existing thin-film solar cell production lines and possessing the potential for large-scale industrial application.

[0023] 3. The yttrium-doped CdS thin film prepared by this invention can be used as a buffer layer in chalcogenide thin-film solar cells, significantly improving the overall performance of the device. Experimental results show that the CZTSSe solar cell based on the yttrium-doped CdS thin film buffer layer of this invention achieves a photoelectric conversion efficiency of 15.19%, a Voc of 572.1 mV, and a Voc loss reduced to 0.252 eV. These performance indicators are among the highest efficiency levels reported in the current field. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the preparation method of the present invention; Figure 2 This is a schematic diagram illustrating the reaction principle of the preparation method of the present invention; Figure 3 X-ray diffraction (XRD) patterns of the thin films prepared in Comparative Example 1 and Example 1; Figure 4 The X-ray photoelectron spectroscopy (XPS) spectra of the thin films prepared in Comparative Example 1 and Example 1 are shown. Figure 5 Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) images of the thin films prepared in Comparative Example 1 and Example 1 are shown; where (a) is the AFM image of Comparative Example 1, (c) is the AFM image of Example 1, (b) is the KPFM image of Comparative Example 1, and (d) is the KPFM image of Example 1. Figure 6 The optical bandgap test results are for the thin films prepared in Comparative Example 1 and Example 1. Detailed Implementation

[0025] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0026] The p-type chalcogenide absorber film of this invention can be any one of copper zinc tin sulfur selenide (CZTSSe), copper zinc tin selenide (CZTSe), copper indium gallium selenide (CIGS), or antimony selenide (Sb₂Se₃). The following description uses CZTSSe as an example. This invention does not limit the preparation method of the CZTSSe absorber film; any conventional technique in the art is acceptable, including solution deposition or vapor deposition. Taking the solution deposition method as an example, the specific preparation process of the CZTSSe absorber film in the following examples and comparative examples is as follows: (1) Preparation of precursor solution: According to the elemental molar ratio Cu / (Zn+Sn)=0.75, Zn / Sn=1.1, 0.4157 g of cuprous chloride, 0.6585 g of zinc acetate dihydrate, 0.894 g of tin tetrachloride pentahydrate and 1.5186 g of thiourea were dissolved in 10 mL of 2-methoxyethanol and stirred in a heating mantle at 60 ℃ for 2 h until the solution was completely dissolved and turned into a light yellow transparent state, thus obtaining the CZTS precursor solution; (2) Spin coating and pretreatment of precursor films: The precursor solution was uniformly coated on a soda-lime glass substrate with a molybdenum (Mo) back electrode and spin-coated at 3000 rpm for 28 s. Then, it was annealed in air at 290 ℃ for 2 min. The above spin coating-annealing process was repeated 11 times to obtain Cu2ZnSnS4 (CZTS) precursor films; (3) Selenization treatment: The prepared CZTS precursor film was placed in a graphite box, and an appropriate amount of selenium particles were added. The box was then placed in a rapid thermal annealing furnace and heated to 570 °C under a nitrogen atmosphere. The temperature was held for 1100 s, and after cooling, a Cu2ZnSn(S,Se)4 (CZTSSe) absorber film was formed on the substrate with a Mo back electrode. The resulting CZTSSe absorber film had a thickness of about 1.5-2.0 μm, good crystallinity, large grain size, and no obvious secondary phase, making it suitable for subsequent buffer layer deposition and device assembly.

[0027] (I) Implementation Examples Example 1 Example 1 provides a method for preparing a yttrium-doped CdS thin film, comprising the following steps: (1) According to the volume ratio of cadmium sulfate solution, ammonia water, thiourea solution and water, 0.015 mol / L cadmium sulfate solution, 1.2 mol / L thiourea solution and 28% ammonia water were added to water at three-minute intervals. After stirring evenly, a mixed solution was obtained. The conductive substrate with the CZTSSe absorption layer film formed above was immersed in the mixed solution and initially deposited at 68 °C for 6 min until the film showed a uniform duck blood color. (2) Take out the conductive substrate after initial deposition in step (1) and quickly transfer it to a yttrium nitrate solution with a concentration of 0.04 mol / L. Soak it at 68 ℃ for 60 s. Take it out and quickly place it in the mixed solution described in step (1) and continue to deposit at 68 ℃ for 60 s. Repeat the above soaking and deposition operation 5 times. After the deposition is completed, rinse the sample surface with flowing deionized water for 30 s to completely remove soluble salts. Then dry it with high-purity nitrogen to obtain yttrium-doped CdS film.

[0028] This embodiment also provides a yttrium-doped CdS thin film, which is prepared by the above preparation method.

[0029] Example 2 Example 2 provides a method for preparing yttrium-doped CdS thin films, which are obtained by the following preparation process: (1) According to the volume ratio of cadmium sulfate solution, ammonia water and thiourea solution 1:1.2:0.8:7, add 0.03 mol / L cadmium sulfate solution, 2 mol / L thiourea solution and 28% ammonia water to water at three-minute intervals, stir evenly to obtain a mixed solution; immerse the conductive substrate with the CZTSSe absorber layer film formed above into the mixed solution, and initially deposit at 68°C for 6 min until the film shows a uniform duck blood color; (2) Take out the conductive substrate after initial deposition in step (1) and quickly transfer it to a 0.02 mol / L yttrium nitrate solution. Soak it at 68 °C for 60 s. Take it out and quickly place it in the mixed solution described in step (1) and continue to deposit at 68 °C for 60 s. Repeat the above soaking and deposition operation 5 times. After the deposition is completed, rinse the sample surface with flowing deionized water for 30 s to completely remove soluble salts. Then dry it with high-purity nitrogen to obtain a yttrium-doped CdS film.

[0030] This embodiment provides a yttrium-doped CdS thin film, which is prepared by the above-described preparation method.

[0031] Example 3 Example 3 provides a method for preparing yttrium-doped CdS thin films, which are obtained by the following preparation process: (1) According to the volume ratio of cadmium sulfate solution, ammonia water and thiourea solution of 1:1.5:1:8, add 0.005 mol / L cadmium sulfate solution, 0.5 mol / L thiourea solution and 25% ammonia water to water, with an addition interval of three minutes, and stir evenly to obtain a mixed solution; immerse the conductive substrate with the CZTSSe absorber layer film formed above into the mixed solution, and initially deposit at 68°C for 6 min until the film shows a uniform duck blood color; (2) Take out the conductive substrate after initial deposition in step (1) and quickly transfer it to a 0.06 mol / L yttrium nitrate solution. Soak it at 68 °C for 60 s. Take it out and quickly place it in the mixed solution described in step (1) and continue to deposit at 68 °C for 60 s. Repeat the above soaking and deposition operation 5 times. After the deposition is completed, rinse the sample surface with flowing deionized water for 30 s to completely remove soluble salts. Then dry it with high-purity nitrogen to obtain a yttrium-doped CdS film.

[0032] This embodiment provides a yttrium-doped CdS thin film, which is prepared by the above-described preparation method.

[0033] (ii) Comparative Example Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that the initial deposition time of step (1) in Example 1 is adjusted to 11 min and step (2) is omitted, that is, the film prepared by Comparative Example 1 is a CdS film.

[0034] Comparative Example 2 Comparative Example 1 is basically the same as Example 1, except that the yttrium nitrate solution in Example 1 is replaced with an indium nitrate solution, i.e., an indium-doped CdS thin film is prepared.

[0035] (III) Application Examples The thin films prepared in Examples 1-3 and Comparative Examples 1-2 were applied to copper-zinc-tin-sulfur-selenium solar cells. The cells were assembled in the order of substrate / back electrode / absorber layer / buffer layer / window layer / top electrode, resulting in Application Examples 1-3 and Comparative Application Examples 1-2. The substrate was soda-lime glass, the back electrode was a molybdenum layer, the absorber layer was the aforementioned copper-zinc-tin-sulfur-selenium thin film, the buffer layer was the thin film prepared in Examples 1-3 or Comparative Examples 1-2, the window layer was an intrinsic zinc oxide layer (i-ZnO) and an indium tin oxide layer (ITO), and the top electrode was silver.

[0036] (iv) Test Examples 1. Characterization of the physical properties of CdS-doped thin films Structure and morphology characterization: For the films obtained in Example 1 and Comparative Example 1, the crystal structure of the films was analyzed by XRD, the elemental composition and chemical valence state of the films were analyzed by XPS, and the surface morphology of the films was observed by AFM.

[0037] Surface electrical properties characterization: The change in surface work function of the thin film was tested using KPFM.

[0038] Figure 3 These are the XRD test results of the yttrium-doped CdS thin film (Y-CdS) prepared in Example 1 and the CdS thin film (Control-CdS) in Comparative Example 1. Figure 3 It can be seen that, compared with CdS thin films, the full width at half maximum (FWHM) of the (002) plane diffraction peak of yttrium-doped CdS thin films is significantly narrower. This indicates that after yttrium doping, the micro-strain and defect density (such as dislocations and vacancies) inside the CdS lattice are reduced, the crystallinity of the crystal is improved, and the impurity byproducts are reduced. This structural optimization is beneficial to improving carrier mobility and reducing the recombination of photogenerated carriers at grain boundaries.

[0039] Figure 4 The XPS test results are for the thin films obtained in Example 1 and Comparative Example 1; wherein Figure 4 (a) is the S 2p spectrum of yttrium-doped CdS and CdS. Figure 4 (b) is the Y 3d spectrum of yttrium-doped CdS. Figure 4 (c) and Figure 4 (d) are the Cd3d spectra of CdS and yttrium-doped CdS, respectively. Figure 4 (e) and Figure 4 (f) are the O 1s spectra of CdS and yttrium-doped CdS, respectively. From Figure 4 The O 1s and Cd 3d spectra of (cf) show that, compared with the CdS film, the characteristic peak areas of Cd(OH)2 and CdO in Example 1 are reduced and the peak intensities are decreased. This indicates that the relative content of Cd(OH)2 in the yttrium-doped CdS film is reduced. This shows that soaking in yttrium ion solution not only successfully incorporated yttrium ions into CdS, but also suppressed the side reaction to generate Cd(OH)2, which is beneficial to reducing the source of deep-level defects and further improving the crystallinity of the film.

[0040] Figure 5 Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) images of the thin films prepared in Comparative Example 1 and Example 1 are shown; Figure 5 (a) is an atomic force microscope (AFM) image of the thin film prepared in Comparative Example 1. Figure 5 (c) is an atomic force microscope (AFM) image obtained in Example 1. Figure 5 (b) is a Kelvin probe force microscope (KPFM) image of the thin film prepared in Comparative Example 1. Figure 5 (d) is a Kelvin probe force microscopy (KPFM) image of the thin film prepared in Example 1. Figure 5 (a) and Figure 5 (c) It can be seen that the yttrium-doped CdS film prepared in Example 1 (except for a few irregular growth points) exhibits a uniform granular shape with a surface roughness of 10.6 nm; while the CdS film prepared in Comparative Example 1 (except for a few irregular growth points) exhibits a relatively dispersed granular shape with a surface roughness of 13.8 nm. Therefore, compared to Example 1, the flatness of the film produced in Comparative Example 1 is reduced due to the omission of the yttrium ion solution soaking step. This difference is attributed to the fact that the preparation method of this invention utilizes Y... 3+ The high affinity for oxygen and hydroxyl groups effectively suppresses the formation of insulating secondary phases such as Cd(OH)2 and CdO during CdS deposition, reducing the density of interface defect states at the source, improving film quality, and contributing to the reduction of interface states; Figure 5 (b) and Figure 5 (d) It can be seen that the average surface contact potential difference of Comparative Example 1 is higher, at -19 mV, while the surface contact potential of Example 1 is not only uniform but also -104 mV, a decrease of 85 mV. This means that electrons can escape from the surface more easily. This indicates that the doped yttrium ions increase the carrier concentration, drive the Fermi level to shift towards the conduction band direction, which is beneficial for optimizing the band matching between the window layer and the absorption layer, increasing the built-in potential, and thus promoting the effective extraction and transport of electrons at the interface.

[0041] 2. Photoelectric performance testing of CdS-doped thin films The carrier concentration, carrier mobility, and optical band gap of the thin films obtained in Example 1 and Comparative Examples 1-2 were measured and calculated using a Hall effect meter and a UV-Vis spectrophotometer. The results are shown in Table 1. The optical band gap test diagrams of the thin films obtained in Comparative Example 1 and Example 1 are shown below. Figure 6 As shown.

[0042] Table 1 Performance data of the thin films obtained in Example 1 and Comparative Examples 1-2 As can be seen from the above, compared with Comparative Examples 1-2, Example 1 shows significant improvements in carrier concentration, optical band gap, and carrier mobility. The most significant improvement is in carrier concentration, which is nearly 150% higher than in Comparative Example 1. This means reduced energy loss during transmission, which is more conducive to the transport of photoelectrons. Specifically, the preparation process utilizes Y... 3+ The high affinity for oxygen and hydroxyl groups inhibits the formation of insulating secondary phases such as Cd(OH)2 and CdO during CdS deposition, reducing the density of interfacial defect states at the source. Simultaneously, the introduced Y... 3+Y can be formed Cd Donor defects increase the n-type carrier concentration in the CdS thin film, thereby further enhancing the built-in electric field of the heterojunction and promoting the separation of photogenerated carriers.

[0043] 3. The buffer layer / CZTSSe absorber heterojunctions constructed in Example 1 and Comparative Examples 1-2 were tested: The conduction band / valence band shift and built-in potential of each heterojunction were tested by using a UPS / XPS combination, and the results are shown in Table 2.

[0044] Table 2. Conduction band / valence band offset values ​​and embedded potential test data As can be seen from the above, compared with the heterojunctions formed in Comparative Examples 1 and 2, Example 1, through Y... 3+ Doping effectively modulates the band structure of CdS as a buffer layer, resulting in a more ideal band alignment with the CZTSSe absorber layer: the reduction of CBO lowers the electron transport barrier, allowing photogenerated electrons to be injected more smoothly from the absorber layer into the buffer layer, reducing transmission losses; while the increase of VBO enhances the blocking ability for holes, effectively suppressing hole leakage into the buffer layer and interface recombination. Combined with Y... 3+ The improved crystal quality, reduced defect density, and significantly increased carrier concentration brought about by doping, along with the synergistic optimization mechanism of "small CBO and large VBO", are consistent with the test results of the built-in potential. Both show that they are beneficial to the separation and transport efficiency of photogenerated carriers. Therefore, the yttrium-doped CdS buffer layer prepared in Example 1 has better photoelectric performance in copper-zinc-tin-sulfur-selenium solar cells.

[0045] 4. Performance tests were conducted on the copper-zinc-tin-sulfur-selenium solar cells assembled in the corresponding use case 1 and the comparative application examples 1-2: At AM 1.5G, 100 mW / cm 2 Under the test conditions, the photovoltaic performance of the copper-zinc-tin-sulfur-selenium solar cells assembled in the corresponding use case 1 and comparative application examples 1-2 was tested, and the results are shown in Table 3.

[0046] Table 3. Photovoltaic performance test data of solar cells in Application Example 1 and Comparative Application Examples 1-2 As can be seen from the above, compared with Application Example 1, the performance of the solar energy device prepared in Application Example 1 is comprehensively improved, which is consistent with the results shown in Tables 1 and 2. Application Example 1 enhances the built-in electric field of the heterojunction by increasing the n-type carrier concentration of the CdS thin film, optimizes band alignment (CBO and VBO) and interface quality, thereby improving carrier recombination lifetime and photoelectric conversion efficiency. The specific analysis is as follows: On the one hand, the ideal band structure formed by reducing CBO and increasing VBO significantly improves the separation and transport efficiency of photogenerated carriers, significantly suppresses nonradiative recombination (carrier recombination lifetime is increased by about 160%), and directly reduces the reverse saturation current density and VBO. OC Losses, which in turn drive the open-circuit voltage (V OC ) significantly improved; on the other hand, Y 3+ Doping effectively reduces the defect state density, Y 3+ The high affinity of doping for oxygen and hydroxyl groups competitively suppresses the formation of insulating secondary phases such as Cd(OH)2 and CdO during the CBD process, reducing the interface defect state density at the source. Simultaneously, the increased n-type carrier concentration promotes the effective separation of photogenerated electrons, resulting in a lower short-circuit current density (J / L). SC Simultaneously increasing, the fill factor (FF) also steadily increased. With significant improvements in microscopic parameters such as recombination lifetime, defect density, and reverse saturation current, the overall photoelectric conversion efficiency (PCE) of the device ultimately achieved a significant improvement. Furthermore, compared to Comparative Application Example 2 (In-doped), Application Example 1 outperformed the In-doped scheme in all performance indicators, especially V. OC The advantages of Y (572.1 mV vs. ~541 mV) and PCE (15.19% vs. ~14.5%) are obvious. This indicates that Y 3+ Doping can not only increase the carrier concentration (compared to In) 3+ (Similar function), it can also optimize band arrangement and suppress secondary phases, which is In 3+ It possesses unique advantages that traditional doped ions do not have. Specifically, In 3+ While doping can provide free electrons and increase carrier concentration, its smaller ionic radius leads to lattice contraction in CdS, which in turn shifts the conduction band bottom upward and increases CBO, forming a potential barrier that is unfavorable to electron transport; meanwhile, In 3+ OH - Its affinity is relatively weak, and it cannot effectively suppress the formation of secondary phases such as Cd(OH)2 and CdO, thus the interface defect state density remains high. In contrast, Y 3+ With its suitable ionic radius, unique 4f electronic configuration, and high affinity for oxygen / hydroxyl groups, it achieves a triple synergistic effect of increased carrier concentration, optimized band structure, and suppressed secondary phases, thereby obtaining superior device performance.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a yttrium-doped CdS thin film, characterized in that, Includes the following steps: (1) Add cadmium salt solution, ammonia water and thiourea solution to water in sequence and stir until homogeneous to obtain a mixed solution; A conductive substrate with a thin film of P-type chalcogenide absorber layer is immersed in the mixed solution and subjected to initial deposition by water bath heating. (2) Take out the conductive substrate after initial deposition in step (1), immerse it in yttrium salt solution, and then deposit it in the mixed solution. Repeat the immersion and deposition operation 4-6 times. After washing and drying, yttrium-doped CdS film is obtained.

2. The method for preparing yttrium-doped CdS thin films according to claim 1, characterized in that, The yttrium salt solution mentioned in step (2) is any one of yttrium nitrate solution, yttrium chloride solution or yttrium sulfate solution; the concentration of yttrium ions in the yttrium salt solution is 0.02-0.06 mol / L.

3. The method for preparing yttrium-doped CdS thin films according to claim 1, characterized in that, The soaking temperature in step (2) is 65-75 ℃ and the soaking time is 30-90 s.

4. The method for preparing yttrium-doped CdS thin films according to claim 1, characterized in that, The deposition temperature in step (2) is 65-75 ℃ and the time is 30-90 s.

5. The method for preparing yttrium-doped CdS thin films according to claim 1, characterized in that, The initial deposition temperature in step (1) is 65-75 °C and the time is 5-7 min.

6. The method for preparing yttrium-doped CdS thin films according to claim 1, characterized in that, The concentration of the cadmium salt solution in step (1) is 0.005-0.03 mol / L, the concentration of the thiourea solution is 0.5-2.0 mol / L, and the mass concentration of the ammonia water is 25-28%; the volume ratio of the cadmium salt solution, thiourea solution, ammonia water and water is 1:(0.5-1):(1.2-1.5):(7-8).

7. The method for preparing yttrium-doped CdS thin films according to claim 1, characterized in that, The P-type chalcogenide absorber film mentioned in step (1) is any one of copper zinc tin sulfur selenide, copper zinc tin selenide, copper indium gallium selenide, or antimony selenide.

8. A yttrium-doped CdS thin film, characterized in that, It is prepared by the preparation method of any one of claims 1-7.

9. An application of the yttrium-doped CdS thin film according to claim 8, characterized in that, The yttrium-doped CdS thin film was used as a buffer layer in a chalcogenide thin-film battery.

10. A chalcogenide thin-film battery, characterized in that, It includes a p-type chalcogenide absorber layer and a buffer layer, wherein the buffer layer is disposed between the p-type chalcogenide absorber layer and the transparent conductive layer, and forms a heterojunction with the p-type chalcogenide absorber layer; the buffer layer is the yttrium-doped CdS thin film as described in claim 8; the p-type chalcogenide absorber layer is any one of copper zinc tin sulfide selenide, copper indium gallium selenide, copper zinc tin selenide, or antimony selenide.

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