CZTSSe absorption layer doped with Sb and Na elements and preparation method and application of CZTSSe absorption layer

Abstract

The invention discloses a CZTSSe absorption layer doped with Sb and Na elements, and when a flexible CZTSSe thin-film solar cell absorption layer is prepared, Sb and Na are doped into the absorption layer. The invention further provides a solar cell comprising the absorption layer and a method for improving the bending stability of the flexible CZTSSe thin-film solar cell by applying the method. According to the method, growth of crystal grains can be effectively promoted, interface recombination can be reduced, and generation of internal defects of the thin film can be inhibited, so that the internal stress of the cell is reduced, the bending stability of the flexible CZTSSe thin-film solar cell is improved, the internal stress of the solar cell is reduced from-6.40 GPa to-3.20 GPa, and meanwhile, due to reduction of the internal stress, the bending stability of the flexible CZTSSe thin-film solar cell is improved. The mechanical strength of the battery is also improved, when NaF with the thickness of 20 nm and Sb with the concentration of 0.8 mol / L are doped, the PCE attenuation amplitude of the battery is only 8%, and the PCE attenuation amplitude is obviously reduced.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and particularly to a method for improving the bending stability of flexible CZTSSe thin-film solar cells by co-doping with Na and Sb. Background Art

[0002] The energy issue has always been a core topic that cannot be ignored in the development process of human society. Currently, the rapid global economic growth and industrialization process mainly rely on the large consumption of disposable fossil energy. This development model poses a severe challenge to the sustainable supply of energy. Therefore, the transformation and upgrading of the energy structure have become the key to promoting the sustainable development of the world. Among many new energy sources, solar energy, with its clean and renewable characteristics, is regarded as the most ideal alternative to traditional fossil fuels.

[0003] As a new generation of photovoltaic technology after single-crystalline silicon and polycrystalline silicon cells, new thin-film solar cells show great development potential and attract wide attention from the academic and industrial circles. Currently, new thin-film solar cells such as amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS) are being widely studied. Due to the development of new flexible substrates (such as stainless steel, Ti foil, flexible glass, etc.), it has promoted the development of traditional rigid thin-film solar cells towards flexible thin-film solar cells. However, the energy conversion efficiency of a-Si is relatively low and it cannot be applied to flexible substrates. CdTe contains the highly toxic element cadmium, which violates the principle of safety and non-toxicity. CIGS contains rare elements In and Ga, which limits its large-scale production and use. To solve the above problems, researchers are committed to finding a material with high photoelectric conversion efficiency, non-toxicity, rich raw materials, and low price. Therefore, copper zinc tin sulfur selenium (CZTSSe) has become a new research hotspot.

[0004] However, the actual conversion efficiency of flexible CZTSSe solar cells is still lower than the theoretical limit. The main reasons are the residual stress in flexible devices and the relatively high defect density in CZTSSe thin films. These reasons will affect the bending stability of the battery and further affect the photoelectric conversion efficiency of the battery. Summary of the Invention

[0005] Object of the Invention: Aiming at the deficiencies of the prior art, the present invention provides a method for improving the bending stability of flexible CZTSSe thin-film solar cells. Co-doping with Sb and Na in the CZTSSe absorption layer can effectively inhibit the generation of internal defects in the thin film, promote the growth of grains, improve the quality of the thin film, and thus improve the bending stability of flexible CZTSSe thin-film solar cells.

[0006] To solve the above technical problems, the present invention discloses a CZTSSe absorption layer doped with Sb and Na elements, which is prepared by the following method:

[0007] (1) Mix Cu(CH3COO)2·H2O, Zn(CH3COO)2·2H2O, SnCl2·2H2O, CH4N2S and SbCl3 and add them to a solvent, and stir to obtain an Sb-doped CZTS precursor solution;

[0008] (2) Prepare a NaF thin film layer by sputtering;

[0009] (3) Prepare a CZTS metal preform layer by spin coating. Spin coat the Sb-doped CZTS precursor solution obtained in step (1) on the NaF thin film layer obtained in step (2), and then preheat it on a hot stage. Repeat the steps of spin coating and preheating several times to obtain a CZTS metal preform layer;

[0010] (4) Put the CZTS metal preform layer prepared in step (3) into a single-zone tube annealing furnace for selenization annealing to obtain an Sb- and Na-codoped CZTSSe absorption layer.

[0011] The thickness of the Sb- and Na-codoped CZTSSe absorption layer is 0.8 - 1.4 μm.

[0012] In step (1), the concentration of Cu(CH3COO)2·H2O is 0.42 - 0.68 mol / L, the concentration of Zn(CH3COO)2·2H2O is 0.24 - 0.43 mol / L, the concentration of SnCl2·2H2O is 0.29 - 0.41 mol / L, the concentration of CH4N2S is 1.96 - 2.75 mol / L, the concentration of SbCl3 is 0.8 - 2 mol / L, and the solvent is dimethylformamide.

[0013] In step (2), the sputtering conditions are as follows: the base vacuum in the vacuum sputtering chamber is 5×10 -4 -7×10 -4 Pa, the sputtering rate is 10 nm / min - 20 nm / min, and the thickness of the NaF thin film does not exceed 30 nm.

[0014] In step (3), the rotation speed of spin coating the CZTS metal preform layer on the NaF thin film layer is 4500 - 5800 r / min, the time is 21 - 29 s, the temperature of the hot stage is 280 - 330 °C, the preheating time is 2 - 4 min, and the number of repetitions is 13 - 21 times.

[0015] In step (4) described above, the selenization temperature is 562 - 592 °C, the holding time is 9 - 11 min, the heating rate is 45 - 55 °C / min, and the N2 flow rate is 55 - 60 sccm.

[0016] The present invention further provides a method for improving the bending stability of a flexible CZTSSe thin-film solar cell. When preparing the absorption layer of the flexible CZTSSe thin-film solar cell, Sb and Na are doped into the absorption layer. Among them, Sb doping is achieved by adding SbCl3 to the CZTS precursor solution, and Na doping of the CZTSSe absorption layer is realized by preparing a NaF thin film layer on the CZTS metal prefabricated layer and then selenizing it.

[0017] Preferably, the concentration of SbCl3 in the CZTS precursor solution is not higher than 1.2 mol / L, the thickness of the NaF thin film does not exceed 30 nm, and the thickness of the CZTSSe absorption layer co-doped with Sb and Na is 0.8 - 1.4 μm.

[0018] The present invention also provides a flexible CZTSSe thin-film solar cell, and the flexible CZTSSe thin-film solar cell includes the CZTSSe absorption layer doped with Sb and Na elements as described above.

[0019] Specifically, the structure of the flexible CZTSSe thin-film solar cell includes a flexible substrate Ti, a Mo back electrode, a CZTSSe absorption layer, a CdS buffer layer, an i-ZnO window layer, an ITO transparent conductive layer, and an Ag electrode. Among them, the prepared flexible substrate Ti has a size of 2×2 cm 2 , and a thickness of 50 - 80 μm; the prepared Mo back electrode has a thickness of 800 - 1100 nm; the prepared CZTSSe absorption layer has a thickness of 1.1 - 1.5 μm; the prepared CdS buffer layer has a thickness of 55 - 75 nm; the prepared i-ZnO window layer has a thickness of 40 - 80 nm; the prepared ITO transparent conductive layer has a thickness of 160 - 260 nm.

[0020] Preferably, the substrate used is a Ti substrate, the Mo back electrode is prepared by DC sputtering, the CdS buffer layer is prepared by chemical bath deposition, the i-ZnO window layer and the ITO transparent conductive layer are formed by magnetron sputtering, and the Ag layer is prepared by evaporation. Beneficial effects: Compared with the prior art, the present application has the following advantages:

[0021] (1) By co-doping Sb and Na in the CZTSSe absorption layer, the present invention effectively inhibits the generation of crystal defects inside the thin film, promotes grain growth, reduces interface recombination, and finally improves the photoelectric conversion efficiency of the battery.

[0022] (2) By reducing the internal stress of the battery, the present invention further improves the mechanical strength of the battery, so that after the battery undergoes a certain degree of bending, the efficiency of the battery does not decrease significantly, and the bending stability of the battery is improved. Description of the Drawings

[0023] Figure 1 Stress diagrams of flexible CZTSSe thin films under undoped, Sb-doped (SbCl3: 0.8 mol / L), and Na-Sb co-doped (SbCl3: 0.8 mol / L, NaF: 20 nm) conditions;

[0024] Figure 2 J-V curves of flexible CZTSSe thin film solar cells under undoped, Sb-doped (SbCl3: 0.8 mol / L), and Na-Sb co-doped (SbCl3: 0.8 mol / L, NaF: 20 nm) conditions;

[0025] Figure 3 Variation diagrams of the photoelectric conversion efficiency of flexible CZTSSe thin film solar cells under undoped, Sb-doped (SbCl3: 0.8 mol / L), and Na-Sb co-doped (SbCl3: 0.8 mol / L, NaF: 20 nm) conditions at different bending times. Specific implementation manners

[0026] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. The described embodiments are only partial examples of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0027] Comparative example 1

[0028] The structure of the CZTSSe cell prepared in this comparative example is: Ti substrate / Mo back electrode / CZTSSe absorption layer / CdS buffer layer / i-ZnO window layer / ITO transparent conductive layer / Ag electrode.

[0029] The specific steps are as follows:

[0030] Step 1: Prepare the Ti substrate. First, put cleansing powder and dishwashing liquid into a beaker containing the substrate respectively, and rinse the substrate with deionized water. Then, put the substrate into beakers containing alcohol, acetone, and ultrapure water in sequence, perform ultrasonic cleaning for 15 min, and finally dry it with a nitrogen gun for standby.

[0031] Step 2: Prepare the back electrode Mo layer. Prepare the Mo layer on a titanium foil with a size of 2×2 cm 2 , a thickness of 50 μm by DC sputtering method. The sputtering gas pressure is high first and then low. When sputtering, use a Mo target with a diameter of 60 mm (purity of 99%). When sputtering, first pump the background vacuum of the sputtering chamber to 6×10 -4Pa, then open the argon gas cylinder valve and introduce Ar gas with a flow rate of 80 sccm. Carry out deposition for 10 min under the conditions of a DC sputtering power of 240 - 260 W and a chamber vacuum of 0.1 Pa. Then, reduce the flow rate of Ar gas by 10 sccm every 1 min. Finally, when the Ar gas flow rate is 20 sccm, continue sputtering for 8 - 10 min to finally obtain a Mo back electrode layer with a thickness of approximately 1000 nm.

[0032] Step 3: Prepare the CZTSSe precursor solution. Sequentially mix Cu(CH3COO)2·H2O (0.53 mol / L), Zn(CH3COO)2·2H2O (0.31 mol / L), SnCl2·2H2O (0.34 mol / L), and CH4N2S (2.25 mol / L) into 10 ml of dimethylformamide (DMF, AR) to obtain a precursor solution, and continuously stir it at 60 °C for 6 minutes to obtain a clear yellow solution.

[0033] Step 4: Prepare the CZTSSe metal prefabricated layer. Spin-coat the CZTS precursor solution on the Mo layer at a rotation speed of 5000 r / min for 25 s, and preheat it on a hot plate at 300 °C for 2 - 3 min. Repeat the above process 15 times to finally obtain the CZTS metal prefabricated layer.

[0034] Step 5: Prepare the CZTSSe absorption layer. Place the obtained CZTS metal prefabricated layer into a single-temperature zone tube annealing furnace for selenization annealing, where the selenization temperature is 583 °C, and finally obtain the CZTSSe absorption layer.

[0035] Step 6: Prepare the CdS buffer layer by chemical bath deposition method. First, weigh 140 mL of ultrapure water, 20 mL of a CdSO4 solution with a concentration of 0.015 mol / L, 20 mL of a thiourea solution with a concentration of 0.6 mol / L, and 20 mL of ammonia water, and pour them into a glass container in sequence to react for 5 - 9 minutes. During the reaction, stir the solution with a stirrer in the container. The stirring speed is 14 r / min for the first 4 min and 9 r / min for the last 4 min. After the reaction ends, take out the sample, rinse it repeatedly with ultrapure water, and finally place it on a hot plate at a temperature of 58 - 78 °C for drying to finally prepare a CdS buffer layer with a thickness of 60 nm.

[0036] Step 7: Deposit the i-ZnO window layer and ITO transparent conductive layer by magnetron sputtering. When sputtering the i-ZnO window layer, the sputtering power is 150 W, the sputtering gas pressure is 0.15 Pa, the sputtering time is 8 min, the Ar flow rate is 60 sccm, and the finally prepared i-ZnO window layer film thickness is 50 nm. When sputtering the ITO transparent conductive layer, the sputtering power is 30 W, the sputtering gas pressure is 0.1 Pa, the sputtering time is 4000 s, the Ar flow rate is 30 sccm, and the finally prepared ITO film thickness is 220 nm, the sheet resistance is about 20 Ω / □, and the transmittance in the visible light range exceeds 85%.

[0037] Step 8: Prepare the silver electrode by evaporation method.

[0038] Analyze the obtained products. Figure 1 2θ and sin 2 ψ linear fitting diagram of CZTSSe thin films under different doping. Using Figure 1 We can calculate the residual stress of the battery. The detection method and calculation formula are as follows: The Omega stress XRD method is used to calculate the residual stress of the battery. Its basic principle is that when there is stress in the sample, the crystal plane spacing will change. When performing Bragg diffraction on it, the generated diffraction peak will shift, and the size of the shift distance is related to the stress size. The selected Ψ incident angle range in this experiment is 5° - 50°, and the calculation of the residual stress is based on the (112) diffraction peak of the CZTSSe thin film. The specific formula is as follows

[0039]

[0040] Here E is the Young's modulus of the battery, μ is the Poisson's ratio, θ0 is the diffraction degree of the battery without stress, and M is Figure 1 The slope of the fitting line in. Therefore, according to the above formula, the residual stress of the CZTSSe thin film can be calculated. It can be seen from the figure that when Sb is not doped, the residual stress of the CZTSSe thin film is -6.40 GPa. Figure 2 J-V curves of the battery under different doping. Table 1 shows the battery parameters calculated according to Figure 2 Among them, Voc is the open circuit voltage, Jsc is the short circuit current, FF is the fill factor, and PCE is the conversion efficiency. It can be seen from the table that for Comparative Example 1, its PCE is 3.24%, the open circuit voltage (Voc) is 334.12 mV, the current density (Jsc) is 23.89 mA / cm 2 , and the fill factor (FF) is 40.71%. Figure 3 It is the attenuation of the device PCE (power conversion efficiency) under different bending times and different doping. It can be seen from the figure that under the condition of 200 bends, the PCE of Comparative Example 1 decreased by 19%.

[0041] Example 1

[0042] The structure of the CZTSSe solar cell fabricated in this example is: Ti substrate / Mo back electrode / Sb-doped CZTSSe absorber layer / CdS buffer layer / i-ZnO window layer / ITO transparent conductive layer / Ag electrode.

[0043] The preparation method of each layer in the solar cell is the same as that in Comparative Example 1, and the only difference is that SbCl3 is added to the precursor solution with a concentration of 0.8 mol / L, and finally a CZTSSe absorber layer is fabricated.

[0044] The obtained product was analyzed. It can be seen from Figure 1 that when the concentration of SbCl3 is 0.8 mol / L, the residual stress of the CZTSSe thin film is -4.94 GPa. Compared with Comparative Example 1, the residual stress of the CZTSSe thin film is reduced by 1.45 GPa. It can be seen from Table 1 and Figure 2 that the PCE of the sample obtained in Example 1 is 4.41%, the open-circuit voltage (Voc) is 347.13 mV, the current density (Jsc) is 25.38 mA / cm 2 , and the fill factor (FF) is 50.12%. Compared with Comparative Example 1, the electrical performance of the solar cell is improved.

[0045] Example 2

[0046] The structure of the CZTSSe solar cell fabricated in this example is: Ti substrate / Mo back electrode / Na- and Sb-codoped CZTSSe absorber layer / CdS buffer layer / i-ZnO window layer / ITO transparent conductive layer / Ag electrode.

[0047] The preparation method of each layer in the solar cell is the same as that in Example 1, and the only difference is that a NaF thin film is prepared by evaporation on the back electrode Mo layer, and during the selenization annealing process, an alloying reaction occurs with the CZTS metal preform layer, and finally a Na- and Sb-codoped CZTSSe absorber layer is obtained. The thickness of the NaF thin film is 20 nm.

[0048] The obtained product was analyzed by comparison. It can be seen from Figure 1It can be seen that when the concentration of SbCl3 is 0.8 mol / L and the thickness of the Na film is 20 nm, the residual stress of the CZTSSe thin film is -3.20 GPa. Compared with Comparative Example 1 and Example 1, the residual stress of the CZTSSe thin film is reduced by 1.45 GPa and 3.20 GPa respectively. Table 1 shows the performance parameters of flexible CZTSSe thin film solar cells with different doping concentrations under undoped, Sb-doped, and Na-Sb co-doped conditions. It can be seen from the table that for the Sb-doped solar cells, the cells prepared at 0.8 mol / L have the best performance. Subsequently, with the Sb doping concentration fixed (0.8 mol / L) and the thickness of the NaF doping being 20 nm, the solar cells prepared under Na-Sb co-doping have the best performance. From Table 1 and Figure 2 it can be seen that the PCE of the sample obtained in Example 2 is 5.36%, the open-circuit voltage (Voc) is 530.98 mV, and the current density (Jsc) is 26.71 mA / cm 2 , and the fill factor (FF) is 57.25%. Compared with Comparative Example 1, the electrical performance of the solar cells in Example 2 is further improved. From Figure 3 it can be seen that under the condition of 200 bending cycles, the PCE value of Example 2 decreased by 8%. Compared with Comparative Example 1, by doping a 20-nm-thick NaF film, the attenuation amplitude of the PCE of the battery is significantly reduced, and the performance of the battery is greatly retained. It shows that appropriate Na and Sb co-doping can effectively alleviate the damage of the microstructure of the flexible CZTSSe thin film after the battery is bent.

[0049] Table 1 Performance parameters of flexible CZTSSe thin film solar cells with different doping concentrations under undoped, Sb-doped, and Na-Sb co-doped conditions

[0050]

[0051]

[0052] In the present invention, by doping Na and Sb elements into the CZTSSe absorption layer, the grain growth is promoted, the generation of crystal defects inside the thin film is effectively inhibited, the internal stress of the CZTSSe thin film is greatly reduced, and finally the photoelectric conversion efficiency of the battery is improved. In addition, by the method of reducing the internal stress of the battery in the present invention, the bending stability and conversion efficiency of the battery are improved, and even in a harsh bending environment, a high conversion efficiency PCE can still be maintained.

[0053] The present invention provides an idea and method for improving the residual stress of the absorption layer of a flexible CZTSSe thin-film solar cell. There are many methods and ways to specifically implement this technical solution. The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A CZTSSe absorption layer doped with Sb and Na elements, characterized in that, It is prepared by the following method: (1) Add Cu(CH3COO)2·H2O, Zn(CH3COO)2·2H2O, SnCl2·2H2O, CH4N2S and SbCl3 into a solvent, and stir to obtain an Sb-doped CZTS precursor solution; (2) Prepare a NaF thin film layer by sputtering method; (3) Prepare a CZTS metal preform layer by spin coating. Spin coat the Sb-doped CZTS precursor solution obtained in step (1) on the NaF thin film layer obtained in step (2), and then preheat it on a hot stage. Repeat the steps of spin coating and preheating several times to obtain a CZTS metal preform layer; (4) Put the CZTS metal preform layer prepared in step (3) into a single-zone tube annealing furnace for selenization annealing to obtain an Sb- and Na-codoped CZTSSe absorption layer.

2. The CZTSSe absorption layer according to claim 1, wherein The thickness of the Sb- and Na-codoped CZTSSe absorption layer is 0.8 - 1.4 μm.

3. The CZTSSe absorption layer according to claim 1, wherein In the CZTS precursor solution obtained in step (1), the concentration of Cu(CH3COO)2·H2O is 0.42 - 0.68 mol / L, the concentration of Zn(CH3COO)2·2H2O is 0.24 - 0.43 mol / L, the concentration of SnCl2·2H2O is 0.29 - 0.41 mol / L, the concentration of CH4N2S is 1.96 - 2.75 mol / L, the concentration of SbCl3 is 0.8 - 2 mol / L, and the solvent is dimethylformamide.

4. The CZTSSe absorption layer according to claim 1, wherein In step (2), the sputtering conditions are as follows: the background vacuum in the vacuum sputtering chamber is 5×10 -4 -7×10 -4 Pa, the sputtering rate is 10 nm / min - 20 nm / min, and the thickness of the NaF thin film does not exceed 30 nm.

5. The CZTSSe absorption layer according to claim 1, characterized in that, In step (3), the spin coating speed of the CZTS metal preform layer on the NaF thin film layer is 4500 - 5800 r / min, the time is 21 - 29 s, the temperature of the hot stage is 280 - 330 °C, the preheating time is 2 - 4 min, and the number of repetitions is 13 - 21 times.

6. The CZTSSe absorption layer according to claim 1, characterized in that, In step (4), the selenization temperature is 562 - 592 °C, the holding time is 9 - 11 min, the heating rate is 45 - 55 °C / min, and the N2 flow rate is 55 - 60 sccm.

7. A method for improving the bending stability of flexible CZTSSe thin-film solar cells, characterized in that, When preparing the absorption layer of a flexible CZTSSe thin film solar cell, Sb and Na are doped into the absorption layer. Among them, Sb doping is achieved by adding SbCl3 into the CZTS precursor solution, and Na doping of the CZTSSe absorption layer is achieved by preparing a NaF thin film layer on the CZTS metal preform layer and then selenizing.

8. The method according to claim 7, characterized in that, The concentration of SbCl3 in the CZTS precursor solution is not higher than 1.2 mol / L, the thickness of the NaF thin film does not exceed 30 nm, and the thickness of the Sb- and Na-codoped CZTSSe absorption layer is 0.8 - 1.4 μm.

9. A flexible CZTSSe thin film solar cell, characterized in that, The flexible CZTSSe thin film solar cell described above comprises the CZTSSe absorption layer doped with Sb and Na elements according to any one of claims 1 - 6.

10. The flexible CZTSSe thin-film solar cell according to claim 9, characterized in that, The described flexible CZTSSe thin film solar cell structure includes a flexible substrate Ti, a Mo back electrode, a CZTSSe absorption layer, a CdS buffer layer, an i-ZnO window layer, an ITO transparent conductive layer, and an Ag electrode. Among them, the prepared flexible substrate Ti has a thickness of 50 - 80 μm; the prepared Mo back electrode has a thickness of 800 - 1100 nm; the prepared CZTSSe absorption layer has a thickness of 1.1 - 1.5 μm; the prepared CdS buffer layer has a thickness of 55 - 75 nm; the prepared i-ZnO window layer has a thickness of 40 - 80 nm; the prepared ITO transparent conductive layer has a thickness of 160 - 260 nm.

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