A kind of CIGSe thin film and its surface treatment method and application

Abstract

The application discloses a CIGSe thin film and a surface treatment method and application thereof, and belongs to the technical field of thin film solar cells. The application forms a mercapto group and a deprotonated form thereof of cysteamine hydrochloride under weak alkaline conditions by placing the CIGSe thin film in a surface treatment solution, and the mercapto group and the deprotonated form thereof are coordinated with copper ions in a Cu 2‑x Se secondary phase on the surface of the CIGSe thin film to form a soluble complex. The method can selectively remove the Cu 2‑x Se secondary phase on the surface of the CIGSe thin film, reduces a surface defect state density, improves interface quality of an absorption layer / buffer layer, and thus improves performance of the CIGSe solar cell. The application has simple process, low cost and good repeatability, and can be applied to preparation of high-efficiency CIGSe thin film solar cells and laminated solar cells.

Description

Technical Field

[0001] This invention relates to the field of thin-film solar cell technology, specifically to a CIGSe thin film and its surface treatment method and application. Background Technology

[0002] Copper indium gallium selenide (Cu(In,Ga)Se2, or CIGSe for short) thin-film solar cells are considered one of the most promising thin-film photovoltaic technologies for industrialization due to their advantages such as high absorption coefficient, tunable bandgap, excellent low-light performance, and good radiation resistance. Currently, laboratory-certified efficiencies have exceeded 23%, showing broad application prospects in flexible photovoltaics, building-integrated photovoltaics, and tandem solar cells. To further improve the photoelectric conversion efficiency of CIGSe solar cells, copper-rich growth processes are typically used to promote the growth of the absorber layer grains and improve the crystallinity of the thin film. However, Cu2O2 deposits easily form on the surface of CIGSe thin films prepared under copper-rich conditions. 2-x Se secondary phase. Due to Cu 2-x Se has high conductivity, and its presence will change the surface chemical composition and electrical properties of the absorption layer, increase the density of interface defect states and non-radiative recombination centers, affect the uniform growth of the subsequent buffer layer, and thus lead to enhanced interface recombination, reduced open-circuit voltage and degraded device performance.

[0003] Currently, for the Cu on the surface of CIGSe absorber layer 2-x To remove the accumulation of Se secondary phase, researchers typically employ wet chemical etching. For example, KCN etching can effectively remove Cu from the surface of CIGSe films. 2-x Se secondary phase can reduce leakage current loss and interfacial recombination caused by it. However, KCN has high toxicity and environmental risks, and has high requirements for operational safety and waste liquid treatment, which is not conducive to large-scale production and industrial application. In addition, existing treatment methods usually focus on secondary phase removal, and the synergistic control of surface defects in the absorber layer and the absorber layer / buffer layer interface is still insufficient. Therefore, it is necessary to develop a safe, mild, rapid and highly selective surface treatment technology to remove Cu. 2-x The Se secondary phase improves surface and interface properties, thereby enhancing the performance of CIGSe solar cells. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a CIGSe thin film, its surface treatment method, and its applications, in order to achieve Cu on the surface of the CIGSe thin film. 2-x Selective removal of the Se secondary phase effectively reduces the surface defect state density, improves interface properties, and suppresses interface recombination, thereby significantly improving solar cell performance.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A surface treatment method for CIGSe thin films is provided, comprising the following steps: (1) Add a thiol-containing organic compound to a solvent, and then add an alkaline regulator to adjust the pH of the solution to 7.0-10.0 to obtain a surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) for surface treatment; (3) Clean and dry the CIGSe film after surface treatment in step (2) to obtain the surface-treated CIGSe film.

[0006] Furthermore, the concentration of the thiol-containing organic compound is 0.1-5M.

[0007] Furthermore, the thiol-containing organic compound is at least one of cysteine ​​hydrochloride, cysteine, mercaptoacetic acid, mercaptoethanol, and 3-mercaptopropionic acid.

[0008] Furthermore, the solvent is at least one of deionized water, ethanol, methanol, and isopropanol.

[0009] Furthermore, the alkalinity regulator is at least one of ammonia, sodium hydroxide, potassium hydroxide, and organic amine.

[0010] Furthermore, the surface treatment time is 1-10 minutes.

[0011] Furthermore, the cleaning and drying process specifically involves cleaning with deionized water and drying with nitrogen blowing, vacuum drying, or heat treatment.

[0012] The present invention provides a CIGSe thin film prepared by the above-described surface treatment method.

[0013] This invention provides an application of the above-mentioned CIGSe thin film in the preparation of CIGSe solar cells.

[0014] The present invention also provides a CIGSe solar cell comprising the above-described CIGSe thin film.

[0015] The present invention has the following beneficial effects: (1) This invention utilizes the active thiol group in cysteine ​​hydrochloride and Cu 2-x Copper ions in the Se secondary phase undergo coordination to achieve Cu on the CIGSe thin film surface. 2-x The selective removal of the secondary Se phase does not require high temperature or complex vacuum processes, and has the advantages of simple process, low cost and easy implementation.

[0016] (2) The present invention can effectively reduce the surface defect state density and tail state defect level of CIGSe thin film, improve the surface chemical environment of the absorber layer, and improve the film quality.

[0017] (3) The present invention can optimize the interface properties between the absorption layer and the buffer layer, reduce the non-radiative recombination loss at the interface, and improve the separation and transport capabilities of photogenerated carriers.

[0018] (4) The CIGSe solar cells prepared by the surface treatment method of the present invention have higher open circuit voltage, fill factor and photoelectric conversion efficiency, and can be widely used in high-efficiency CIGSe solar cells, flexible CIGSe solar cells and CIGSe-based tandem solar cells, with good application prospects and industrialization value. Attached Figure Description

[0019] Figure 1 For the solar cells of Example 7 and the comparative example JV Curve comparison chart; Figure 2 XPS images of Cu 2p at etching depths of 0 nm, 2 nm, and 4 nm for the CIGSe films of Example 7 and the comparative example, respectively. Figure 3 Raman spectra of CIGSe thin films in Example 7 and the comparative example; Figure 4 The Urbach energy of the CIGSe solar cells in Example 7 and the comparative example ( E U Fitted graph. Detailed Implementation

[0020] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0021] Example 1: A surface treatment method for a CIGSe thin film includes the following steps: (1) Add cysteamine hydrochloride to deionized water to prepare a 1M cysteamine hydrochloride solution; then add ammonia to adjust the pH to 7.8 to obtain the surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) and treat it at room temperature for 2 min; (3) Rinse the CIGSe film after surface treatment in step (2) with deionized water for 30 seconds, and then dry it under nitrogen atmosphere to obtain the treated CIGSe film.

[0022] Example 2: A surface treatment method for a CIGSe thin film includes the following steps: (1) Add cysteamine hydrochloride to deionized water to prepare a 0.5M cysteamine hydrochloride solution; then add ammonia to adjust the pH to 8.0 to obtain the surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) and treat it at room temperature for 1 min; (3) Rinse the CIGSe film after surface treatment in step (2) with deionized water for 30 seconds, and then dry it under nitrogen atmosphere to obtain the treated CIGSe film.

[0023] Example 3: A surface treatment method for a CIGSe thin film includes the following steps: (1) Add cysteamine hydrochloride to deionized water to prepare a 1.5M cysteamine hydrochloride solution; then add ammonia to adjust the pH to 8.3 to obtain the surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) and treat it at room temperature for 3 min; (3) Rinse the CIGSe film after surface treatment in step (2) with deionized water for 30 seconds, and then dry it under nitrogen atmosphere to obtain the treated CIGSe film.

[0024] Example 4: A surface treatment method for a CIGSe thin film includes the following steps: (1) Add mercaptoacetic acid to ethanol to prepare a 3M mercaptoacetic acid solution; then add ammonia to adjust the pH to 10.0 to obtain the surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) and treat it at room temperature for 10 min; (3) Rinse the CIGSe film after surface treatment in step (2) with deionized water for 30 seconds, and then dry it under nitrogen atmosphere to obtain the treated CIGSe film.

[0025] Example 5: A surface treatment method for a CIGSe thin film includes the following steps: (1) Add mercaptoethanol to a mixed solvent of methanol and deionized water to prepare a 0.1M mercaptoethanol solution; then add ammonia to adjust the pH to 9.0 to obtain the surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) and treat it at room temperature for 5 min; (3) Rinse the CIGSe film after surface treatment in step (2) with deionized water for 30 seconds, and then dry it under nitrogen atmosphere to obtain the treated CIGSe film.

[0026] Example 6: A surface treatment method for a CIGSe thin film includes the following steps: (1) Add 3-mercaptopropionic acid to isopropanol to prepare a 0.5M 3-mercaptopropionic acid solution; then add ammonia to adjust the pH to 8.5 to obtain the surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) and treat it at room temperature for 8 min; (3) Rinse the CIGSe film after surface treatment in step (2) with deionized water for 30 seconds, and then dry it under nitrogen atmosphere to obtain the treated CIGSe film.

[0027] Example 7: A CIGSe solar cell includes a soda-lime glass substrate, a molybdenum back electrode, a CIGSe thin film treated as described in Example 1, a Zn(O,S) / CdS buffer layer, an i-ZnO / Al:ZnO window layer, and a Ni:Al gate electrode. Its fabrication process is as follows: (1) Clean the soda-lime glass substrate with ultrasonic cleaning for 30 min and dry it at 80℃ for 30 min to ensure that the surface is clean and free of contamination; (2) A double Mo back electrode was deposited on a pretreated soda-lime glass substrate using DC magnetron sputtering. The first Mo layer was 500 nm thick (deposition conditions: sputtering pressure 0.1 Pa, sputtering power 200 W), and the second Mo layer was 600 nm thick (deposition conditions: sputtering pressure 0.3 Pa, sputtering power 320 W). (3) A CIGSe absorber layer was prepared by a three-step co-evaporation method, and the thickness of the absorber layer was approximately 1.8 μm; (4) The CIGSe absorber layer in step (3) was surface treated using the surface treatment method of Example 1 to obtain a surface-treated CIGSe film. (5) A Zn(O,S) and CdS buffer layers were sequentially deposited on the CIGSe film surface in step (4) using a chemical bath deposition method, as follows: First, 0.3M zinc source, 0.1M thioacetamide and 4.0M ammonia were added to 500mL of deionized water and reacted at 65℃ and 400r / min for 5min to form a Zn(O,S) layer with a thickness of about 50nm; then the sample was transferred to 500mL of aqueous solution containing 0.04M cadmium source, 2.5M thiourea and 3.0M ammonia and deposited at 82℃ and 400r / min for 3min to form a CdS layer with a thickness of about 30nm. (6) A 100 nm thick i-ZnO layer (sputtering process: sputtering temperature 150 °C, sputtering pressure 0.6 Pa) and a 350 nm thick Al:ZnO window layer (sputtering process: sputtering temperature 180 °C, sputtering pressure 0.4 Pa) are deposited sequentially on the surface of the product obtained in step (5) using radio frequency magnetron sputtering. (7) A 30 nm Ni and a 100 nm Al gate electrode were prepared by electron beam evaporation to complete the preparation of CIGSe solar cells.

[0028] Comparative example: A CIGSe solar cell. Its preparation process differs from that of Example 7 only in that the surface treatment in step (4) is not performed.

[0029] Experimental example: (1) A solar simulator (SAN-EIXES-500T1 (AAA grade)) was used to test the solar cells prepared in Example 7 and the comparative example. JV Test; the test source meter was a Keithley 2420, using a four-wire connection; the test standard spectrum was AM 1.5G, with a light intensity of 1000 Wm. -2 The ambient temperature was 25°C. Example 7 and the comparative example solar cells... JV Curve pairs, for example Figure 1 As shown, the parameters of the solar cells prepared in Example 7 and the comparative example are compared in Table 1.

[0030] Table 1. Comparison of parameters between Example 7 and the comparative example solar cells.

[0031] Depend on Figure 1 As shown in Table 1, compared with the control group without cysteine ​​hydrochloride treatment, the open-circuit voltage of the solar cell in Example 7 increased from 862mV to 883mV, and the short-circuit current density increased from 19.29mA / cm². 2 Increased to 20.91 mA / cm 2 The fill factor increased from 76.92% to 77.72%, and the photoelectric conversion efficiency increased from 12.79% to 14.35%. These results indicate that cysteine ​​hydrochloride surface treatment helps improve the surface and interface properties of the CIGSe absorber layer, reduce carrier recombination loss, and improve the separation and collection efficiency of photogenerated carriers, thereby achieving a synergistic improvement in various photovoltaic performance parameters of solar cells.

[0032] (2) The CIGSe films in Example 7 and the comparative example were analyzed using a Thermo Scientific ESCALAB 250Xi instrument (Thermo). The Cu 2p X-ray photoelectron spectra of the CIGSe films in Example 7 and the comparative example at different etching depths are shown below. Figure 2 As shown, Cu 2p atoms appeared in all samples at approximately 932 eV and 952 eV. 3 / 2 and Cu 2p 1 / 2 Characteristic peaks, and no obvious Cu was observed. 2+ Satellite peaks indicate that copper in the film mainly retains its original chemical valence state before and after treatment, and cysteine ​​hydrochloride treatment did not induce a significant copper oxidation reaction. XPS results on the surface of the CIGSe absorber layer and at etching depths of 2 nm and 4 nm show that the Cu 2p signal of the sample was weakened after cysteine ​​hydrochloride treatment, indicating a decrease in the copper content in the near-surface region. This is further supported by the mercapto groups in cysteine ​​hydrochloride on Cu... + The coordination effect indicates that this treatment mainly acts on the near-surface region of the CIGSe film, reducing the Cu content in the surface and near-surface regions by promoting the dissolution of Cu from the Cu-rich components. 2-x The content of Se secondary phase.

[0033] (3) The CIGSe absorption layers in Example 7 and the comparative example were detected using LabRAM HR Evolution (HORIBA Scientific). The Raman spectra of the CIGSe absorption layers in Example 7 and the comparative example are as follows: Figure 3 As shown. Both groups of samples are at approximately 182 cm. -1 and 222cm -1 The presence of A1 and B2 vibrational characteristic peaks corresponding to the CIGSe chalcopyrite structure at approximately 260 cm⁻¹ indicates that the cysteine ​​hydrochloride treatment did not significantly damage the main crystal structure of CIGSe. The untreated comparative sample showed peaks at approximately 260 cm⁻¹. -1 The area has relatively obvious Cu 2-x The characteristic peak of the Se secondary phase was observed, but this peak was significantly weakened after treatment with cysteine ​​hydrochloride. These results indicate that cysteine ​​hydrochloride can effectively reduce Cu content in the surface and near-surface regions of the CIGSe absorber layer. 2-x The content of the Se secondary phase is reduced, while the CIGSe main phase structure is well maintained, which is beneficial for its dependence on Cu. 2-x The selective removal of the Se secondary phase provides further evidence.

[0034] In Example 7 and the Comparative Example, the CIGSe solar cells E U The fitting results are as follows Figure 4 As shown. E UThe EQE was obtained by fitting the data, and the EQE was tested using a Zolix Solar Cell Scan 100. The comparative device without cysteine ​​hydrochloride treatment... E U The processed device of Example 7 has a voltage of 21.2 meV. E U 20.3 meV. Before and after processing. E U Being at similar levels indicates that the devices V OC The improvement primarily stems from optimization of the near-junction region, rather than changes in the intrinsic properties of the absorption layer. Surface treatment effectively reduces interfacial recombination. Combined with XPS, Raman spectroscopy, and device performance test results, it is demonstrated that cysteine ​​hydrochloride treatment can improve the near-surface and interfacial properties while maintaining the quality of the CIGSe bulk material, thereby reducing carrier recombination losses.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surface treatment method for a CIGSe thin film, characterized in that, Includes the following steps: (1) Add a thiol-containing organic compound to a solvent, and then add an alkaline regulator to adjust the pH of the solution to 7.0-10.0 to obtain a surface treatment solution; (2) Immerse the CIGSe film in the surface treatment solution of step (1) for surface treatment; (3) Clean and dry the CIGSe film after surface treatment in step (2) to obtain the surface-treated CIGSe film.

2. The surface treatment method according to claim 1, characterized in that, The concentration of the thiol-containing organic compound is 0.1-5M.

3. The surface treatment method according to claim 1 or 2, characterized in that, The thiol-containing organic compound is at least one selected from cysteine ​​hydrochloride, cysteine, thioglycolic acid, mercaptoethanol, and 3-mercaptopropionic acid.

4. The surface treatment method according to claim 1, characterized in that, The solvent is at least one of deionized water, ethanol, methanol, and isopropanol.

5. The surface treatment method according to claim 1, characterized in that, The alkalinity regulator is at least one of ammonia, sodium hydroxide, potassium hydroxide, and organic amine.

6. The surface treatment method according to claim 1, characterized in that, The surface treatment time is 1-10 minutes.

7. The surface treatment method according to claim 1, characterized in that, The cleaning and drying process specifically involves cleaning with deionized water and drying with nitrogen blowing, vacuum drying, or heat treatment.

8. A CIGSe film prepared by the surface treatment method according to any one of claims 1-7.

9. The application of the CIGSe thin film according to claim 8 in the preparation of CIGSe solar cells.

10. A CIGSe solar cell, characterized in that, Includes the CIGSe thin film as described in claim 8.

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