CN114447151A - A kind of preparation method of cadmium sulfide thin film for solar cell - Google Patents

Abstract

A cadmium sulfide film for solar cells is prepared through dissolving cadmium salt in organic solvent to obtain solution of cadmium salt, dissolving sulfur source in organic solvent to obtain solution of sulfur source, mixing said solution of cadmium salt with said solution of sulfur source, adding glacial acetic acid, adding cadmium chloride or zinc chloride as modifier, preparing solution of cadmium sulfide, spin coating on the surface of substrate, and annealing. The CdS film (1) prepared by the method is simple and low in synthesis cost; (2) the cadmium waste liquid is less and is environment-friendly; (3) the prepared cadmium sulfide film has uniform thickness, strong controllability, good film continuity and low roughness, and can realize large-area preparation; (4) the doping of O, Cl elements and the like is realized, the energy band structure and the electrical property of the film are improved, and the cell efficiency is effectively improved when the film is used for a solar cell.

Description

A kind of preparation method of cadmium sulfide thin film for solar cell

technical field

The invention relates to the technical field of thin film preparation, in particular to a preparation method of a cadmium sulfide thin film for solar cells.

Background technique

Cadmium sulfide (chemical formula CdS) is an n-type semiconductor material, which is a commonly used buffer layer material in thin film solar cells such as copper indium gallium selenide, cadmium telluride, and antimony selenide. There is no more suitable substitute in industrial production. For example, journal papers: IEEE J.Photovoltaics 2019, 9, 1863 and Nat. Energy 2019, 4, 837 reported thin-film solar cells with efficiencies greater than 20% based on cadmium sulfide thin films. However, the preparation of high-quality cadmium sulfide thin films mainly relies on the chemical bath deposition technique (CBD), both in the laboratory and in industrial production. Since the substrate to be coated needs to be completely immersed in the solution during the preparation process, and the solution cannot be reused, a large amount of wastewater containing cadmium will be generated, causing serious environmental problems. Although some technologies for preparing CdS in vacuum have also been reported, such as the journal paper Applied Materials Today, 2019, 16, 367 reported a method for preparing CdS thin films by radio frequency magnetron sputtering, but the technical equipment requirements and manufacturing costs are relatively high , and the vacuum chamber is easy to be polluted, and dust is easily generated during the cleaning and maintenance process, which may cause heavy metal damage to personnel.

SUMMARY OF THE INVENTION

Based on the above technical problems, the purpose of the present invention is to provide an energy-saving and environment-friendly preparation method of a cadmium sulfide thin film for solar cells. The films prepared by this method have excellent electrical properties.

The object of the present invention is achieved through the following technical solutions:

A method for preparing a cadmium sulfide thin film for solar cells, characterized in that: dissolving cadmium salt in an organic solvent to prepare a cadmium salt solution; dissolving a sulfur source in the organic solvent to prepare a sulfur source solution; The salt solution and the sulfur source solution are mixed, glacial acetic acid is added, and then cadmium chloride or zinc chloride is added as a modifier to prepare the obtained cadmium sulfide spin coating solution, spin coating on the surface of the substrate, and then annealing. The cadmium salt is a mixture of one or more of cadmium acetate, cadmium acetylacetonate and dimethyl cadmium, the sulfur source is a mixture of one or more of thiourea, ethylene thiourea and thioacetamide, and the organic The solvent is one or a mixture of ethylene glycol methyl ether, ethanol, N,N-dimethylformamide or isopropanol.

Preferably, the cadmium salt is cadmium acetate, the sulfur source is thiourea, and the organic solvent is ethylene glycol methyl ether.

Further, the concentration of the cadmium salt solution is 0.15-0.75 mol/L, and the concentration of the sulfur source solution is 0.15-0.75 mol/L.

Further, the above-mentioned cadmium salt solution and sulfur source solution are mixed according to the ratio of Cd ²⁺ :S ^2- molar ratio of 0.7:1 to 1.3:1.

Further, the dosage ratio of the above-mentioned cadmium salt solution, glacial acetic acid and modifier is 5~20mL:1.5~6mL:2~8mg.

During the preparation process, it was found that cadmium oxide and other substances were easily generated in the spin coating aqueous solution prepared with cadmium salts such as cadmium chloride and chromium sulfate, which resulted in a decrease in the purity of the prepared cadmium sulfide. Alcoholysis occurs, resulting in the deposition of fine particles on the surface of the film, resulting in an increase in the surface roughness of the film. The invention selects specific cadmium salt to dissolve in specific organic solvent, and adds glacial acetic acid to adjust the pH environment of the spin coating solution, inhibits the alcoholysis of the cadmium salt, improves the stability of the spin coating solution, and simultaneously inhibits ionization in the spin coating solution. OH ^- , thereby reducing the subsequent generation of cadmium oxide impurities.

Further, in the above spin coating, the cadmium sulfide spin coating solution is added dropwise on the substrate, and the drop amount is 15-80 μL/cm ² , and then rotated at a rotational speed of 500-1600 rpm for 5-30 s.

Preferably, the dropwise amount of the above spin coating solution is 300 μL/cm ² , and the solution is rotated at a speed of 800 rpm for 10 s.

Further, the temperature of the above annealing is 250-450° C., and the annealing time is 2-45 min.

Most specifically, a method for preparing a cadmium sulfide thin film for solar cells, characterized in that the steps are as follows:

A, one or more of cadmium acetate, cadmium acetylacetonate, dimethyl cadmium is dissolved in one or more of ethylene glycol methyl ether, ethanol, N,N-dimethylformamide or isopropanol In a mixed organic solution, a cadmium salt solution with a concentration of 0.15 to 0.75 mol/L is prepared;

B. One or more of thiourea, ethylene thiourea and thioacetamide are mixed and dissolved in one or more of ethylene glycol methyl ether, ethanol, N,N-dimethylformamide or isopropanol In a mixed organic solution, a sulfur source solution with a concentration of 0.15 to 0.75 mol/L is prepared;

C, get cadmium salt solution and sulfur source solution according to Cd ²⁺ : S ^2- mol ratio is 0.7:1～1.3:1 to carry out controlled mixing, then add glacial acetic _acid and modifier successively, and modifier is CdCl or ZnCl _2. After fully dissolving, a cadmium sulfide spin coating solution is obtained, and the dosage ratio of cadmium salt solution, glacial acetic acid and modifier is 5~20mL: 1.5~6mL: 2~8mg;

D. Add dropwise cadmium sulfide spin coating solution on the substrate according to the amount of 15~80μL/cm ² , and then rotate at 500~1600rpm for 5~30s;

E. Annealing in air or under the protection of inert gas, the annealing temperature is 250~450℃, and the annealing time is 2~45min.

The above-mentioned substrate can be selected from molybdenum glass, ITO glass or FTO glass.

In the preparation of cadmium sulfide thin films for solar cells, the thinner the thickness, the better, but the thinner the thickness, the greater the roughness of the spin-coated thin film, the poorer the uniformity, and the thin film is prone to discontinuity and poor density, resulting in the final The performance of the film is greatly reduced. In addition, when the cadmium sulfide film is prepared by the spin coating method, the bonding force between the cadmium sulfide film and the substrate is weak, and it is easy to peel off.

In the present invention, CdCl ₂ or ZnCl ₂ is added to the spin coating liquid as a modifier to improve the interface energy level matching between the film and the absorption layer, and secondly, the crystallization rate is reduced, the grain size is increased, and the defects on the surface of the grain boundary are reduced , reducing the surface roughness of the film, enhancing the connection between the grain boundaries and the grain boundaries, enhancing the continuity of the film, thereby improving the density of the film, achieving the effect of improving the morphology, and improving the bonding force between the film layers. Among them, Cl ^- forms a doping element, which increases the carrier concentration, thereby improving the charge transport ability, so that even if the film thickness is thin, it can still maintain excellent electrical properties.

The present invention has the following technical effects:

The CdS film prepared by the invention (1) has a simple method, does not require a vacuum environment, and has low synthesis cost; (2) uses less spin coating liquid, less cadmium-containing waste liquid, and is environmentally friendly; (3) the thickness of the prepared cadmium sulfide film is Uniform, strong controllability, the film thickness can be as low as 20nm, and it can still maintain excellent continuity, high density, low roughness, and can realize large-scale preparation; (4) The doping of elements such as O and Cl is realized during the preparation process. It improves the energy band structure and electrical properties of the thin film, and effectively improves the cell efficiency when used in solar cells.

Description of drawings

Fig. 1: The physical picture of the cadmium sulfide thin film prepared by the present invention.

Figure 2: Scanning electron microscope image of the cadmium sulfide thin film prepared by the present invention.

Figure 3: X-ray diffraction pattern of the cadmium sulfide thin film prepared by the present invention.

Fig. 4: JV curve diagram of the solar cell with the FTO/CdS/Sb ₂ Se ₃ /Au structure prepared by the present invention.

Fig. 5: JV curve diagram of the solar cell with Mo/CaS/Sb ₂ Se ₃ /ITO structure prepared by the present invention.

Detailed ways

The present invention will be specifically described by the following examples. It is necessary to point out that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can SUMMARY OF THE INVENTION Some non-essential improvements and adjustments are made to the present invention.

Example 1

A method for preparing a cadmium sulfide thin film for solar cells, the steps are as follows:

Step A: dissolving cadmium acetate in ethylene glycol methyl ether to prepare a cadmium salt solution with a concentration of 0.5mol/L;

Step B: dissolve thiourea in ethylene glycol methyl ether, and prepare a sulfur source solution with a concentration of 0.5 mol/L;

Step C: take the cadmium salt solution and the sulfur source solution for controlled mixing according to the Cd ²⁺ : S ^2- molar ratio of 1.15:1, then add glacial acetic acid and modifier CdCl ₂ in turn, and after fully dissolving, obtain a cadmium sulfide spin coating solution, the dosage ratio of cadmium salt solution, glacial acetic acid and modifier is 10mL:4mL:4mg;

Step D: using ITO glass as the substrate substrate, dripping the cadmium sulfide spin coating solution on the substrate substrate according to the amount of 30 μL/cm ² , and then rotating at a speed of 800 rpm for 10 s to prepare a cadmium sulfide film with a thickness of 50 nm;

Step E: the spin-coated substrate is annealed in air, the annealing temperature is 450° C., and the annealing time is 10 minutes.

As shown in FIG. 2 , the cadmium sulfide thin film prepared in this example has high density, few defects, good thickness uniformity, low surface roughness, and excellent bonding force with the substrate. The X-ray diffraction pattern of the cadmium sulfide film is shown in Figure 3. It can be seen from the figure that other impurities such as cadmium oxide are not detected in the film.

On the basis of the above cadmium sulfide film, a Sb ₂ Se ₃ film with a thickness of 700 nm was prepared by the near-space sublimation method, and an Au film with a thickness of 150 nm was deposited on the film by DC magnetron sputtering to obtain ITO glass/CdS /Sb ₂ Se ₃ /Au thin film solar cells.

Comparative Example 1

Using ITO as the bottoming agent, a layer of cadmium sulfide film with a thickness of 50 nm was prepared on the surface of ITO by chemical water bath method, and then a Sb ₂ Se ₃ film with a thickness of 700 nm and a thickness of 150 nm were sequentially prepared by the same method as in Example 1. The Au thin film was obtained to obtain a thin film solar cell with ITO glass/CdS/Sb ₂ Se ₃ /Au structure.

The cadmium sulfide film prepared in Comparative Example 1 has poor surface thickness uniformity and high surface roughness, and there are many cadmium oxide impurities in the cadmium sulfide film.

The performance of the thin-film solar cells of the ITO glass/CdS/Sb ₂ Se ₃ /Au structure prepared in Example 1 and Comparative Example 1 was tested, and the JV curves of the solar cells were shown in Figure 4: Photoelectric conversion of the solar cells prepared in Example 1 The efficiency PCE is 5.92%, the open-circuit voltage Voc is 0.35V, the short-circuit current density Jsc reaches 32.22mA/cm ² , and the fill factor FF reaches 52.77%, while the photoelectric conversion efficiency PCE of the solar cell prepared in Comparative Example 1 is 4.84%, and the open-circuit voltage The Voc was 0.35V, the short-circuit current density Jsc was 26.22 mA/cm ² , and the fill factor FF was 52.74%.

Example 2

A method for preparing a cadmium sulfide thin film for solar cells, the steps are as follows:

Step A: dissolving cadmium acetate in ethylene glycol methyl ether to prepare a cadmium salt solution with a concentration of 0.5mol/L;

Step B: dissolve thiourea in ethylene glycol methyl ether, and prepare a sulfur source solution with a concentration of 0.5 mol/L;

Step C: take the cadmium salt solution and the sulfur source solution for controlled mixing according to the Cd ²⁺ : S ^2- molar ratio of 1.15:1, then add glacial acetic acid and modifier CdCl ₂ in turn, and after fully dissolving, obtain a cadmium sulfide spin coating solution, the dosage ratio of cadmium salt solution, glacial acetic acid and modifier is 10mL:4mL:4mg;

Step D: Using molybdenum glass as the substrate, a layer of Sb ₂ Se ₃ film with a thickness of 700 nm was prepared on the surface of the molybdenum glass by a near-space sublimation method, and then a cadmium sulfide spin coating solution was added dropwise in an amount of 30 μL/cm ² , The rotation speed is 800r/min, the rotation time is 10s, and the cadmium sulfide film with the thickness of 50nm is prepared;

Step E: placing the spin-coated substrate in an argon atmosphere, and annealing at 300° C. for 5 min.

The cadmium sulfide thin film prepared in this example has high density, few defects, good thickness uniformity, low surface roughness, and excellent bonding force with the substrate.

On the basis of the above cadmium sulfide thin film, an ITO thin film with a thickness of 1 μm was deposited on the thin film by radio frequency magnetron sputtering to prepare a Mo/Sb ₂ Se ₃ /CdS/ITO thin film solar cell.

Comparative Example 2

Steps A, B are consistent with embodiment 2;

Step C: get the cadmium salt solution and the sulfur source solution according to the Cd ²⁺ : S ^2- molar ratio of 1.15: 1 and control mixing, then add glacial acetic acid successively, after fully dissolving, obtain the cadmium sulfide spin coating solution, the cadmium salt solution and the The dosage ratio of glacial acetic acid is 10mL:4mL;

Step D: Using molybdenum glass as the substrate, a layer of Sb ₂ Se ₃ film with a thickness of 700 nm was prepared on the surface of the molybdenum glass by a near-space sublimation method, and then a cadmium sulfide spin coating solution was added dropwise in an amount of 30 μL/cm ² , The rotation speed is 800r/min, the rotation time is 10s, and the cadmium sulfide film with the thickness of 50nm is prepared;

Step E: placing the spin-coated substrate in an argon atmosphere, and annealing at 300° C. for 5 min.

On the basis of the above cadmium sulfide thin film, an ITO thin film with a thickness of 1 μm was deposited on the thin film by radio frequency magnetron sputtering to prepare a Mo/Sb ₂ Se ₃ /CdS/ITO thin film solar cell.

The surface roughness of the cadmium sulfide film prepared in Comparative Example 2 is larger, the defects are obvious, and the film density is poor.

The performance of the Mo/Sb ₂ Se ₃ /CdS/ITO thin film solar cells prepared in Example 2 and Comparative Example 2 was tested, and the JV curve was shown in Figure 5: The photoelectric conversion efficiency PCE of the solar cell prepared in Example 2 was 5.60%, the open-circuit voltage Voc is 0.37V, the short-circuit current density Jsc reaches 27.31mA/cm ² , and the fill factor FF reaches 56.43%; while the photoelectric conversion efficiency PCE of the solar cell prepared in Comparative Example 2 is 5.1%, and the open-circuit voltage Voc is 0.37 V, the short-circuit current density Jsc was 24.98 mA/cm ² , and the fill factor FF was 55.18%.

Example 3

A method for preparing a cadmium sulfide thin film for solar cells, the steps are as follows:

Step A: dissolving cadmium acetylacetonate in ethanol to prepare a cadmium salt solution with a concentration of 0.15mol/L;

Step B: dissolving thioacetamide in an ethanol organic solution, and preparing a sulfur source solution with a concentration of 0.15 mol/L;

C, get cadmium salt solution and sulfur source solution according to Cd ²⁺ :S ^2- mol ratio is 0.7:1 to carry out controlled mixing, then add glacial acetic _acid and CdCl successively modifier, after fully dissolving, obtain cadmium sulfide spin coating solution , the dosage ratio of cadmium salt solution, glacial acetic acid and modifier is 5mL: 1.5mL: 2mg;

D. Drop the cadmium sulfide spin coating solution on the FTO substrate in an amount of 15 μL/cm ² , and then rotate at a speed of 500 rpm for 30 s;

E. Perform annealing in air or under the protection of inert gas, the annealing temperature is 400°C, and the annealing time is 2~45min, to obtain a cadmium sulfide film with a thickness of 22nm.

The cadmium sulfide thin film prepared in this example has high density, few defects, good thickness uniformity, low surface roughness, and excellent bonding force with the substrate.

Example 4

A method for preparing a cadmium sulfide thin film for solar cells, the steps are as follows:

A. Dissolve dimethyl cadmium in N,N-dimethylformamide to prepare a cadmium salt solution with a concentration of 0.75mol/L;

B, ethylene thiourea is dissolved in N,N-dimethylformamide, and is formulated into a sulfur source solution with a concentration of 0.75mol/L;

C, get cadmium salt solution and sulfur source solution according to Cd ²⁺ : S ^2- mol ratio is 1:1 to control mixing, then add glacial acetic acid and modifier ZnCl ₂ successively, after fully dissolving, obtain cadmium sulfide spin coating solution , the dosage ratio of cadmium salt solution, glacial acetic acid and modifier is 20mL:6mL:8mg;

D. Drop the cadmium sulfide spin coating solution on the ITO substrate substrate according to the amount of 80 μL/cm ² , and then rotate at a speed of 1600 rpm for 5 s;

E. Perform annealing in air or under the protection of inert gas, the annealing temperature is 250°C, and the annealing time is 2~45min, to obtain a cadmium sulfide film with a thickness of 60nm.

The cadmium sulfide thin film prepared in this example has high density, few defects, good thickness uniformity, low surface roughness, and excellent bonding force with the substrate.

Claims (7)

1. A preparation method of a cadmium sulfide thin film for a solar cell is characterized by comprising the following steps: dissolving cadmium salt in an organic solvent to prepare a cadmium salt solution, dissolving a sulfur source in the organic solvent to prepare a sulfur source solution, mixing the cadmium salt solution and the sulfur source solution, adding glacial acetic acid, adding cadmium chloride or zinc chloride as a modifier to prepare an obtained cadmium sulfide spin-coating solution, performing spin-coating on the surface of a substrate, and then performing annealing treatment, wherein the cadmium salt is one or more of cadmium acetate, cadmium acetylacetonate and dimethyl cadmium, the sulfur source is one or more of thiourea, ethylene thiourea and thioacetamide, and the organic solvent is one or more of ethylene glycol monomethyl ether, ethanol, N-dimethylformamide or isopropanol.

2. The method of claim 1, wherein the method comprises the following steps: the concentration of the cadmium salt solution is 0.15-0.75 mol/L, and the concentration of the sulfur source solution is 0.15-0.75 mol/L.

3. The method of claim 1 or 2 for preparing a cadmium sulfide thin film for a solar cell, comprising: the cadmium salt solution and the sulfur source solution are according to Cd²⁺:S^2-Mixing at a molar ratio of 0.7:1 to 1.3: 1.

4. A method of preparing a cadmium sulfide thin film for a solar cell according to any one of claims 1 to 3: the dosage ratio of the cadmium salt solution, the glacial acetic acid and the modifier is 5-20 mL: 1.5-6 mL: 2-8 mg.

5. The method of any one of claims 1 to 4, wherein the method comprises the following steps: the spin coating is to drop spin coating solution on the substrate, and the dropping amount is 15-80 mu L/cm²And then rotating at a rotating speed of 500-1600 rpm for 5-30 s.

6. The method of claim 1, wherein the method comprises the following steps: the annealing temperature is 250-450 ℃, and the annealing time is 2-45 min.

7. A preparation method of a cadmium sulfide thin film for a solar cell is characterized by comprising the following steps:

A. dissolving one or more of cadmium acetate, cadmium acetylacetonate and dimethyl cadmium in one or more of ethylene glycol monomethyl ether, ethanol, N-dimethylformamide or isopropanol to prepare a cadmium salt solution with the concentration of 0.15-0.75 mol/L;

B. dissolving one or more of thiourea, ethylene thiourea and thioacetamide in one or more of ethylene glycol monomethyl ether, ethanol, N-dimethylformamide or isopropanol to prepare a sulfur source solution with the concentration of 0.15-0.75 mol/L;

C. taking cadmium salt solution and sulfur source solution according to Cd²⁺:S^2-Mixing the materials in a molar ratio of 0.7: 1-1.3: 1, and then sequentially adding glacial acetic acid and a modifier, wherein the modifier is CdCl₂Or ZnCl₂And after the cadmium sulfide is fully dissolved, obtaining a cadmium sulfide spin-coating solution, wherein the dosage ratio of the cadmium salt solution to the glacial acetic acid to the modifier is 5-20 mL: 1.5-6 mL: 2-8 mg;

D. according to the proportion of 15-80 mu L/cm²Dropwise adding cadmium sulfide spin-coating liquid on the substrate, and then rotating at the rotating speed of 500-1600 rpm for 5-30 s;

E. and annealing in air or under the protection of inert gas, wherein the annealing temperature is 250-450 ℃, and the annealing time is 2-45 min.

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