Passivation method of solar cell absorption layer CIGSe thin film

Abstract

The invention discloses a solar cell absorption layer CIGSe film passivation method, and relates to the technical field of solar cells, the method comprises the following steps: adding a sulfur source and a potassium source into a solvent, and carrying out ultrasonic and stirring treatment to obtain a K2S precursor material; and uniformly coating the K2S precursor material on the surface of the CIGSe thin film, and then carrying out annealing treatment in a vacuum environment. The invention also discloses an application of the passivation method in preparation of a solar cell. According to the method, efficient passivation of the CIGSe absorption layer is achieved based on K2S, the valence band position can be effectively reduced, interface recombination can be inhibited, the performance of the solar cell is remarkably improved, and the method has high application value.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a passivation method for a CIGSe thin film in an absorption layer of a solar cell. Background Art

[0002] Copper indium gallium selenide (CIGS) solar cells are a new generation of photovoltaic devices. Their actual open circuit voltage ( V OC ) is still significantly lower than the theoretical limit, and the serious voltage loss problem restricts the full utilization of the wide bandgap advantage. Studies have shown that the bulk defects and interface recombination centers of the absorption layer are the main causes of V OC The key factor of the loss is that targeted passivation technology is urgently needed. Among the many passivation methods, alkali metal (Na, K, Rb, Cs) post-treatment technology is widely used in CIGS device systems because of its triple optimization mechanism of grain boundary defect passivation, surface energy band regulation and carrier concentration enhancement. Among them, the mainstream method mostly uses vacuum thermal evaporation, which achieves doping by evaporating solid alkali metal fluoride under high temperature (about 400°C) after the device deposition is completed. Although this method is suitable for industrial continuous process and can avoid the introduction of unnecessary impurities, its operation needs to be completed in a high vacuum environment, the process is complex, the equipment cost is high, and the control requirements for evaporation rate and doping dose are extremely strict, which limits its application in low-cost and large-area preparation.

[0003] In contrast, solution-based alkali metal passivation has garnered widespread attention in recent years due to its advantages, including low-temperature processing, simplified equipment, easily controllable doping levels, and excellent uniformity over large areas. By manipulating solution concentration, immersion time, and post-treatment parameters, precise control of doping concentration and distribution can be achieved, demonstrating promising application potential. However, current research on solution-based alkali metal passivation in CIGS solar cells remains relatively limited, lacking a systematic, controllable, and mature process suitable for the fabrication of high-efficiency devices.

[0004] Therefore, there is an urgent need to develop a new, efficient solution-based passivation technology for CIGSe thin-film solar cells to effectively passivate surface and interface defects in the absorber layer, thereby improving the device's open-circuit voltage and overall photoelectric conversion efficiency. This technological breakthrough not only has important theoretical significance but will also provide strong support for the industrialization of next-generation, low-cost, high-performance thin-film solar cells. Summary of the Invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a passivation method for the CIGSe thin film of the solar cell absorption layer. This method realizes efficient passivation of the CIGSe absorption layer based on K2S, can effectively reduce the valence band position, inhibit interface recombination, significantly improve the performance of solar cells, and has great application value.

[0006] The present invention solves the above technical problems with the following technical solution: Provided is a method for passivating a CIGSe thin film in a solar cell absorption layer, comprising the following steps: (1) Adding a sulfur source and a potassium source into a solvent, and subjecting the mixture to ultrasonic and stirring treatment to obtain a K2S precursor material; (2) The K2S precursor material obtained in step (1) is uniformly coated on the surface of the CIGSe film, and then annealed in a vacuum environment.

[0007] Furthermore, in step (1), the sulfur source is at least one of potassium sulfide, sodium sulfide, thioacetamide and thiourea.

[0008] Furthermore, in step (1), the potassium source is at least one of potassium sulfide, potassium hydroxide, potassium chloride and potassium nitrate.

[0009] Furthermore, the solvent is ethanol.

[0010] Furthermore, in step (1), the concentration of sulfur in the K2S precursor material is 0.05-0.3 M, and the concentration of potassium is 0.1-0.6 M.

[0011] Furthermore, in step (1), ultrasonic treatment is performed for 10-30 min; and stirring is performed at 50-400 r / min for 5-40 min.

[0012] Furthermore, in step (2), the coating is performed by spin coating at 1000-5000 r / min for 10-60 s.

[0013] Furthermore, in step (2), the vacuum degree of the vacuum environment is 10 -3 -10 -5 Pa.

[0014] Furthermore, in step (2), the annealing process is: heating to 100-500°C at a rate of 5-20°C / min and keeping the temperature for 2-10 min.

[0015] The present invention also provides application of the passivation method of the CIGSe thin film in the solar cell absorption layer in the preparation of solar cells.

[0016] The present invention also provides a CIGSe solar cell comprising a soda-lime glass substrate, a molybdenum back electrode, a CIGSe film treated by the above passivation method, a Zn(O,S) / CdS buffer layer, an i-ZnO / Al:ZnO window layer and a Ni:Al gate.

[0017] Furthermore, the thickness of the molybdenum back electrode is 500-1500 nm; the thickness of the CIGSe film is 1.5-3.5 μm; the thickness of the Zn(O,S) / CdS buffer layer is 10-90 nm; the thickness of the i-ZnO is 50-120 nm; the thickness of the Al:ZnO is 200-600 nm; the thickness of the Ni gate line is 0.2-0.5 μm; and the thickness of the Al gate line is 50-150 nm.

[0018] The present invention has the following beneficial effects: 1. The present invention provides a high-efficiency surface passivation technology based on potassium sulfide (K2S), which exhibits a dual-functional optimization mechanism in CIGSe batteries: the alkali metal element K can effectively passivate the deep energy level defect state density inside the absorption layer, significantly prolonging the minority carrier lifetime and suppressing non-radiative recombination losses; the chemical reaction between the sulfur (S) element and the surface of the absorption layer can regulate the band structure, lower the valence band position, and make the surface potential distribution more uniform, effectively suppressing the accumulation of charge at the grain boundaries.

[0019] 2. The present method achieves uniform distribution and efficient passivation of K2S on the CIGSe surface through a spin-coating process combined with high-temperature annealing, eliminating the need for complex film-forming processes. This method is characterized by simplicity, low cost, and excellent reproducibility, making it suitable for large-scale production.

[0020] 3. The CIGSe solar cell provided by the present invention adopts K2S passivation treatment, which effectively reduces the interface recombination, V oc With an increase of 33 mV, the device efficiency can be improved by 10.48%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 4 is a comparison diagram of the JV curves and EQE of the solar cells of Example 4 and Comparative Example 1; Figure 2 4 is a comparison chart of the admittance (AS) of the solar cells of Example 4 and Comparative Example 1. DETAILED DESCRIPTION

[0022] The principles and features of the present invention are described below. The examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In the examples, where specific conditions are not specified, conventional conditions or manufacturer-recommended conditions were used. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0023] Example 1 A method for passivating a CIGSe thin film in a solar cell absorption layer comprises the following steps: (1) Add 0.6 g potassium sulfide to 50 mL ethanol, ultrasonicate at 40 kHz for 20 min, and stir at 300 r / min for 10 min to obtain K2S precursor material; (2) The K2S precursor material obtained in step (1) was evenly coated on the surface of the CIGSe film by spin coating at 3000 r / min for 30 s, and then -4 Annealing was carried out in a vacuum environment of Pa; the annealing process was to increase the temperature to 300°C at a rate of 10°C / min and keep the temperature for 5 min.

[0024] Example 2 A method for passivating a CIGSe thin film in a solar cell absorption layer comprises the following steps: (1) Sodium sulfide and potassium chloride were added to ethanol, ultrasonicated for 10 min, and stirred at 50 r / min for 5 min to obtain a K2S precursor material; wherein the concentration of sulfur in the K2S precursor material was 0.05 M and the concentration of potassium was 0.1 M; (2) The K2S precursor material obtained in step (1) was evenly coated on the surface of the CIGSe film by spin coating at 1000 r / min for 60 s, and then -3 Annealing was carried out in a vacuum environment of Pa; the annealing process was to increase the temperature to 100°C at a rate of 5°C / min and keep the temperature for 10 min.

[0025] Example 3 A method for passivating a CIGSe thin film in a solar cell absorption layer comprises the following steps: (1) Thiourea and potassium hydroxide were added to ethanol, ultrasonically treated for 30 min, and stirred at 400 r / min for 40 min to obtain a K2S precursor material; wherein the concentration of sulfur in the K2S precursor material was 0.3 M and the concentration of potassium was 0.6 M; (2) The K2S precursor material obtained in step (1) was evenly coated on the surface of the CIGSe film by spin coating at 5000 r / min for 10 s, and then -5 Annealing was carried out in a vacuum environment of Pa; the annealing process was to increase the temperature to 500°C at a rate of 20°C / min and keep it at that temperature for 2 min.

[0026] Example 4 A CIGSe solar cell comprises a soda-lime glass substrate, a molybdenum back electrode, a CIGSe thin film treated by the passivation method of Example 1, a Zn(O,S) / CdS buffer layer, an i-ZnO / Al:ZnO window layer, and a Ni:Al gate. The CIGSe solar cell preparation process is as follows: (1) After cleaning the calcium glass substrate, vacuum dry it at 80°C for 30 min to ensure that the surface is clean and free of contamination; (2) A double-layer Mo back electrode was deposited on a pretreated soda-lime glass substrate using a DC magnetron sputtering method. The thickness of the first Mo layer was 600 nm (deposition conditions: sputtering pressure 0.2 Pa, sputtering power 200 W), and the thickness of the second Mo layer was 700 nm (deposition conditions: sputtering pressure 0.4 Pa, sputtering power 320 W). (3) A CIGSe absorption layer was deposited on the Mo back electrode using a three-step co-evaporation method (the specific process parameters were: the substrate temperature was set to 420°C, 580°C, and 580°C in sequence, and the film thickness was controlled at 2.0 μm, E g is 1.43 eV); (4) Passivation treatment was performed on the CIGSe film using the method of Example 1; (5) The Zn(O,S) and CdS buffer layers were prepared in sequence by chemical bath deposition. First, 0.2 M Cd source, 0.08 M thioacetamide and 5.0 M ammonia were added to 500 mL deionized water. The deposition temperature was controlled at 62 °C, the deposition time was 8 min, and the stirring speed was 300 r / min. A Zn(O,S) buffer layer with a thickness of 40 nm was obtained. Subsequently, 0.05 M Cd source, 2.0 M thiourea and 3.5 M ammonia were added to 500 mL deionized water. The deposition temperature was controlled at 85 °C, the deposition time was 4 min, and the stirring speed was 500 r / min. A CdS buffer layer with a thickness of 20 nm was obtained. (6) Magnetron sputtering was used to sequentially deposit i-ZnO (deposition conditions: sputtering pressure 0.90 Pa, sputtering power 100 W, deposition thickness 70 nm) and Al:ZnO window layer (Al:ZnO deposition conditions: sputtering pressure 0.5 Pa, sputtering power 300 W, deposition thickness 450 nm); (7) Electron beam evaporation was used to deposit Ni:Al gate electrodes. First, a 0.5 nm thick Ni layer was deposited at a beam current of 0.04 A. Subsequently, an 80 nm thick Al layer was deposited at a beam current of 0.2 A.

[0027] Comparative Example 1 A CIGSe solar cell (different from Example 4 in that the CIGSe is not passivated), comprising a soda-lime glass substrate, a molybdenum back electrode, a CIGSe thin film, a Zn(O,S) / CdS buffer layer, an i-ZnO / Al:ZnO window layer, and a Ni:Al gate; Among them, the thickness of the molybdenum back electrode is 600 nm; the thickness of the CIGSe film is 2 μm; the thickness of the Zn(O,S) / CdS buffer layer is 20 nm; the thickness of the i-ZnO is 70 nm; the thickness of the Al:ZnO is 450 nm; the thickness of the Ni gate line is 0.5 μm; and the thickness of the Al gate line is 80 nm.

[0028] Test Example 1 (1) Comparison of JV curves of Example 4 and comparative solar cells Figure 1 As shown, the illustration is the EQE test result; the comparison of various parameters of the solar cells of Example 4 and Comparative Example 1 is shown in Table 1.

[0029] Table 1 Comparison of parameters of solar cells of Example 4 and Comparative Example 1

[0030] Depend on Figure 1 It can be seen that after the passivation treatment using the method of the present invention, the photoelectric performance of the wide band gap CIGSe device is significantly improved, and the photoelectric conversion efficiency is increased from 14.01% to 15.65%. According to the analysis in Table 1, the device performance is improved after the K2S passivation treatment, among which the device V OC and FF The improvement effect is more obvious. J SC The changes are relatively small.

[0031] The EQE test results show that the K2S passivation treatment has a slight effect on the overall EQE band level. This is because the post-treatment passivates the surface defects of the absorption layer, and the introduction of S inhibits the accumulation of holes at the interface, reduces the interface recombination probability, and increases the carrier lifetime of the film, resulting in an improvement in the entire band. The difference around 500 nm may be due to the fact that the K2S passivation treatment partially changes the surface state of the film, thereby slightly affecting the growth of the subsequent buffer layer. According to the EQE differential, the band gap of the corresponding device is about 1.43 eV. At this time, the device V OC The loss is reduced to 557 mV, which is 33 mV lower than the 590 mV of the unpassivated sample.

[0032] (2) To further analyze the effect of passivation treatment on film defect states, the samples with and without K2S passivation treatment were tested for admittance (AS) and the changes in defect state density under different treatment conditions were analyzed. The results are shown in Figure 2. Figure 2 shown.

[0033] Depend on Figure 2 It can be seen that the defect state density of the untreated sample is 4.66×10 15 cm-3 , which is much higher than the defect state density after treatment of 2.68×10 15 cm -3 This indicates that the K2S passivation treatment effectively suppresses deep energy level defects within the wide-bandgap CIGS absorber layer, thereby improving device performance.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A passivation method for a CIGSe thin film in a solar cell absorption layer, characterized in that: The following steps are involved: (1) Adding a sulfur source and a potassium source into a solvent, and subjecting the mixture to ultrasonic and stirring treatment to obtain a K2S precursor material; (2) The K2S precursor material obtained in step (1) is uniformly coated on the surface of the CIGSe film, and then annealed in a vacuum environment.

2. The passivation method for a CIGSe thin film in a solar cell absorption layer according to claim 1, wherein: In step (1), the sulfur source is at least one of potassium sulfide, sodium sulfide, thioacetamide and thiourea.

3. The passivation method for a CIGSe thin film in a solar cell absorption layer according to claim 1, wherein: In step (1), the potassium source is at least one of potassium sulfide, potassium hydroxide, potassium chloride and potassium nitrate.

4. The passivation method for a CIGSe thin film in a solar cell absorption layer according to claim 1, wherein: In step (1), the concentration of sulfur in the K2S precursor material is 0.05-0.3 M, and the concentration of potassium is 0.1-0.6 M.

5. The passivation method for a CIGSe thin film in a solar cell absorption layer according to claim 1, wherein: In step (2), the coating is performed by spin coating at 1000-5000 r / min for 10-60 s.

6. The passivation method for a CIGSe thin film in a solar cell absorption layer according to claim 1, wherein: In step (2), the annealing process is: heating to 100-500°C at a rate of 5-20°C / min and keeping the temperature for 2-10 min.

7. Use of the passivation method for a CIGSe thin film as an absorber layer of a solar cell according to any one of claims 1 to 6 in the preparation of a solar cell.

8. A CIGSe solar cell, characterized in that: The invention comprises a soda-lime glass substrate, a molybdenum back electrode, a CIGSe film treated by the passivation method according to any one of claims 1 to 6, a Zn(O, S) / CdS buffer layer, an i-ZnO / Al:ZnO window layer and a Ni:Al gate.

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