An activating solution for activating cadmium telluride thin films and its application in the preparation of cadmium telluride thin-film solar cells.

Abstract

This invention provides an activation solution for activating cadmium telluride thin films and its application in the preparation of cadmium telluride thin-film solar cells. The activation solution uses tellurium tetrachloride and cadmium perchlorate hydrate as additives added to an aqueous solution of cadmium chloride. Tellurium tetrachloride generates tellurium dioxide and further tellsurium, which remains on the surface of the cadmium telluride, forming a tellurium-rich layer. Cadmium perchlorate or its hydrate acts as a dispersant, preventing the aggregation of tellurium dioxide and tellurium generated by tellurium tetrachloride, thus promoting the formation of a uniform tellurium-rich layer. Furthermore, cadmium perchlorate hydrate can decompose into cadmium chloride, which can also be used as an activation material. When this activation solution is used in the preparation of cadmium telluride thin-film solar cells, no residual chlorine atoms are detected in the activated cadmium telluride film, and acid etching is unnecessary. A tellurium-rich layer is formed on the crystal surface, and the resulting cadmium telluride solar cell chip achieves a power generation efficiency of 18.5%.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to an activating solution for activating cadmium telluride thin films and its application in the preparation of cadmium telluride thin film solar cells. Background Technology

[0002] Cadmium telluride (CdTe) is a photovoltaic material with excellent photoelectric properties, a direct bandgap of 1.45 eV, high absorption coefficient for visible light, and a theoretical conversion efficiency of up to 30% for single-junction cells. CdTe belongs to the group II-III binary compound semiconductors, is relatively simple in material composition, and is easy to mass-produce industrially, making it one of the most promising thin-film solar cell materials today. Traditional CdTe thin-film solar cell structures include a TCO front electrode on a transparent substrate, a window layer of CdS, an absorber layer of CdTe, and a back contact layer and a back electrode metal layer. In recent years, researchers have begun to use CdSe as the window layer and, by optimizing the thickness of CdSe, have transformed the CdSe / CdTe stack into a CdTe1-based structure. x Se x The gradient bandgap structure of / CdTe replaces the single CdTe absorption layer, and the device achieves better spectral response in both short and long wavelength bands.

[0003] Mass-produced CdTe thin-film solar cell glass typically employs physical vapor deposition (VTD) or near-space sublimation (CSS) processes to fabricate key layers such as CdS, CdSe window layers, and CdTe light-absorbing layers. This method offers advantages such as simple processing, uniform film thickness, and ease of control. However, from a material forming perspective, CdTe films obtained through physical vapor deposition suffer from uneven grain growth, smaller grain size, and more crystal defects due to the influence of heating time and temperature. Furthermore, the lattice mismatch between CdS or CdSe and CdTe leads to the presence of numerous interface states, increasing carrier recombination in the interface region and affecting the performance parameters of CdTe solar cells, such as short-circuit current, open-circuit voltage, fill factor, and conversion efficiency, thus reducing the conversion efficiency of cadmium telluride thin-film solar cells. To ensure uniform grain size and fewer crystal defects, and to minimize defects caused by CdS / CdSe and CdTe interface mismatch, the industry practice is to coat the CdTe film surface with an activation solution on the substrate after CdS / CdSe and CdTe coating, and then perform a high-temperature post-annealing process to improve grain size, solve the CdS / CdSe and CdTe interface mismatch problem, and improve the electrical performance of CdTe thin-film solar cells.

[0004] Current technologies typically involve coating the CdCl2 aqueous solution onto the top of the power generation layer using a chemical bath or spraying method, followed by high-temperature annealing in an activation furnace. While cadmium telluride has a melting point of 1041℃ and cadmium chloride (CdCl2) has a melting point of 568℃, the introduction of CdCl2 during activation allows cadmium telluride to recrystallize at approximately 400℃, increasing grain size and reducing grain boundary defects. However, the chemical bath or spraying method for CdCl2 aqueous solution coating suffers from uneven coating uniformity, resulting in significant variations in coating amount across different areas of the cadmium telluride surface. This makes it difficult to control gas distribution and atmosphere ratio during high-temperature activation in the furnace, leading to uneven distribution of the reaction product chlorine and resulting in localized chlorine residues. These residues remain in the grains as compounds, creating new crystal defects and hindering grain growth.

[0005] Furthermore, due to the high work function of CdTe semiconductor material (5.7 eV), almost no metal can form an ohmic contact with it. Among metals, Pt has the highest work function at 5.39 eV, but it is also relatively low and expensive. Therefore, in industrial production, chemical etching is often used to selectively remove Cd from the surface CdTe to obtain a Te-rich layer. Currently, the industry commonly uses an acidic etching solution to chemically etch the surface of the CdTe film. The acidic solution can contain at least one acid, such as phosphoric acid, sulfuric acid, hydrobromic acid, hydrofluoric acid, nitric acid, hydrochloric acid, etc. This acidic solution preferentially etches Cd on the CdTe surface, leaving a Te-rich layer and forming a film with a Te / Cd molar ratio greater than 1.0 on the surface. However, chemical etching often brings the following problems: toxicity, difficulty in controlling the reaction, and excessive concentration can erode the cadmium telluride grain boundaries, increasing porosity, which in the long run will negatively impact device stability. In summary, developing a novel activating solution and optimizing acid treatment are essential for the field of cadmium telluride thin-film solar cells. Summary of the Invention

[0006] To overcome the problems existing in the prior art, one objective of this invention is to provide an activating solution for activating cadmium telluride thin films. A second objective of this invention is to provide the application of the activating solution for activating cadmium telluride thin films. A third objective of this invention is to provide a method for preparing a cadmium telluride thin-film solar cell. A fourth objective of this invention is to provide a cadmium telluride thin-film solar cell prepared by the above-described method.

[0007] This invention innovatively uses tellurium tetrachloride and cadmium perchlorate hydrate as additives in an aqueous solution of cadmium chloride. Tellurium tetrachloride can generate tellurium dioxide and further generate tellurium. The generated tellurium remains on the surface of cadmium telluride to form a tellurium-rich layer, thus eliminating the need for acid etching. Cadmium perchlorate or its hydrate can play a dispersing role, preventing the aggregation of tellurium dioxide and tellurium generated by tellurium tetrachloride, which is conducive to the formation of a uniform tellurium-rich layer. Furthermore, cadmium perchlorate hydrate can decompose into cadmium chloride, which can also be used as an activating material.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention provides an activating solution for activating cadmium telluride films, comprising the following components: cadmium chloride, tellurium tetrachloride, cadmium perchlorate or its hydrate, and water.

[0010] Preferably, the concentrations of each component in the activation solution satisfy at least one of the following conditions: A) The concentration of cadmium chloride is 50-1000 g / L; B) The concentration of tellurium tetrachloride is 0.01-0.1 mol / L; C) The concentration of cadmium perchlorate or its hydrate is 0.01-0.1 mol / L.

[0011] More preferably, the concentration of cadmium chloride is 100-500 g / L.

[0012] More preferably, the concentration of tellurium tetrachloride is 0.01-0.05 mol / L.

[0013] More preferably, the concentration of cadmium perchlorate or its hydrate is 0.01-0.05 mol / L.

[0014] Preferably, the cadmium perchlorate or its hydrate is cadmium perchlorate hexahydrate.

[0015] The second aspect of the present invention provides the application of the activating solution for activating cadmium telluride thin films described in the first aspect in the preparation of cadmium telluride thin film solar cells.

[0016] The third aspect of the present invention provides a method for preparing a cadmium telluride thin-film solar cell, wherein the cadmium telluride thin-film solar cell includes a cadmium telluride absorber layer, and the preparation method includes the following steps: coating the surface of the cadmium telluride absorber layer with the activation solution described in the first aspect, drying the activation solution, and performing an annealing heat treatment to activate the cadmium telluride absorber layer.

[0017] Preferably, the annealing heat treatment includes the following steps: placing the cadmium telluride absorber layer in a vacuum activation chamber, filling it with an Ar / H2 mixture, and performing an annealing heat treatment.

[0018] This invention employs vacuum heating activation, and more importantly, introduces a reducing gas Ar / H2 mixture during the activation process. The purpose of using a vacuum is to allow chlorine molecules, one of the activation reaction products, and oxygen generated from the thermal decomposition of cadmium perchlorate, to more easily escape to the outside of the film and be removed by the vacuum pump. This reduces chlorine residue inside the cadmium telluride and decreases crystal defects caused by chlorine compounds remaining at the cadmium telluride grain boundaries, thereby improving its impact on grain size. The purpose of using an argon-hydrogen mixture is that when hydrogen is introduced, hydrogen atoms more easily reduce tellurium dioxide molecules on the surface of cadmium telluride at high temperatures, generating tellurium and H2O. Tellurium remains on the surface of cadmium telluride to form a tellurium-rich layer, while H2O evaporates into the vacuum environment upon heating.

[0019] More preferably, the vacuum degree of the vacuum activation chamber is 0.1-1.0 Pa.

[0020] More preferably, the volume percentage of Ar gas in the Ar / H2 mixture is 99%-99.9%.

[0021] More preferably, the flow rate of the Ar / H2 mixture is 500-2000 sccm.

[0022] More preferably, the annealing heat treatment specifically includes the following steps: placing the semi-finished cadmium telluride thin-film solar cell in a vacuum activation chamber and performing a vacuum treatment to reduce the vacuum level to 0.1-1.0 Pa; raising the heating substrate to the activation temperature; and then introducing an Ar / H2 mixed gas into the vacuum activation chamber for annealing heat treatment.

[0023] Semi-finished cadmium telluride thin-film solar cells refer to cadmium telluride thin-film solar cells in which the absorber layer has been prepared but the back contact layer / back electrode has not been prepared.

[0024] Preferably, the annealing heat treatment temperature is 350-450℃.

[0025] Preferably, the annealing heat treatment time is 20-50 minutes.

[0026] Preferably, the drying temperature is 60-100℃.

[0027] Preferably, the coating method includes roller coating, aerosol coating, spraying, or dip coating.

[0028] The dip coating refers to immersing the semi-finished cadmium telluride thin-film solar cell into an activation solution.

[0029] Preferably, the cadmium telluride thin-film solar cell comprises a substrate, a front electrode, a window layer, an absorber layer, a back contact layer, and a back electrode metal layer arranged sequentially.

[0030] More preferably, after the activation process is completed, a back contact layer is plated on the surface of the cadmium telluride absorber layer.

[0031] The fourth aspect of the present invention provides a cadmium telluride thin-film solar cell prepared by the preparation method described in the third aspect.

[0032] The beneficial effects of this invention are: This invention provides an activation solution for activating cadmium telluride thin films. It involves adding tellurium tetrachloride and cadmium perchlorate (or its hydrate) to a conventional cadmium telluride activation solution. Tellurium tetrachloride reacts with water to form molecular-level tellurium dioxide and hydrochloric acid. Tellurium dioxide further generates tellurium, which remains on the surface of the cadmium telluride film, forming a tellurium-rich layer. This eliminates the need for acid treatment after conventional activation processes. Furthermore, the generated hydrochloric acid removes the surface oxide layer formed during subsequent cadmium telluride annealing. Cadmium perchlorate or its hydrate provides dispersion, utilizing the hydrogen bond acceptors in the cadmium perchlorate molecule and the oxygen atoms in tellurium dioxide to form a weak non-covalent interaction, resulting in better dispersion of tellurium dioxide and preventing intermolecular aggregation into larger particles. This creates a stable suspension activation solution, which is beneficial for the subsequent formation of a uniform tellurium-rich layer. Additionally, cadmium perchlorate hydrate can decompose into cadmium chloride, which can also be used as an activation material.

[0033] The present invention also provides the application of the above-mentioned activation solution in the preparation of cadmium telluride thin-film solar cells. No residual chlorine atoms were detected in the cadmium telluride thin film after activation, and the atomic percentage of tellurium was slightly higher than that of cadmium, indicating that a tellurium-rich layer was formed on the crystal surface. Therefore, the obtained cadmium telluride solar cell chip has a better power generation efficiency than that of cadmium telluride solar cell chips using traditional cadmium chloride activation solution. Attached Figure Description

[0034] Figure 1 This is a scanning electron microscope (SEM) image of the cadmium telluride absorption layer in Example 1; Figure 2 EDS energy dispersive spectroscopy analysis of the cadmium telluride absorption layer in Example 1; Figure 3 This is a scanning electron microscope (SEM) image of the cadmium telluride absorption layer in Comparative Example 1. Figure 4 EDS energy dispersive spectroscopy analysis of the cadmium telluride absorber layer in Comparative Example 1; Figure 5 This is a comparison chart of the power generation efficiency of cadmium telluride thin-film solar cells in Example 1 and Comparative Example 1. Detailed Implementation

[0035] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels or prepared and isolated through simple synthesis; unless otherwise specified, the processes employed are conventional processes in the art.

[0036] The activation method of the present invention can be applied to cadmium telluride thin-film solar cells with different film layer structures, and the specific film layer structure can be determined according to the characteristics of different film layers.

[0037] Example 1 This embodiment provides a cadmium telluride thin-film solar cell, the structure of which consists of a transparent substrate, a transparent conductive layer, a window layer, an absorption layer, a back contact layer, and a back electrode layer stacked sequentially. The transparent substrate is a glass substrate.

[0038] The transparent conductive layer can be made of at least one of In2O3, indium tin oxide (In2O3:Sn or ITO), fluorine-doped tin dioxide (SnO2:F or FTO), ZnO, aluminum-doped zinc oxide (ZnO:Al or AZO), and TiN.

[0039] The material of the window layer can be at least one of CdS and CdSe.

[0040] The material of the absorber layer can be CdTe.

[0041] The material of the back contact layer can be at least one of ZnTe, CuO, and CuCl2.

[0042] The back electrode layer can be a Mo / Al / Cr electrode layer.

[0043] The Mo / Al / Cr electrode layer can be a MoN layer, an Al layer, and a Cr layer arranged sequentially.

[0044] The thickness of the transparent conductive layer is 270-550nm; for example, the thickness of the transparent conductive layer is 300-500nm.

[0045] The thickness of the window layer is 27-220nm; for example, the thickness of the window layer is 30-200nm.

[0046] The thickness of the absorption layer is 0.9-6.5 μm; for example, the thickness of the absorption layer is 1-6 μm.

[0047] The thickness of the back contact layer is 15-35nm; for example, the thickness of the back contact layer is 20-33nm; and even further, the thickness of the back contact layer is 30nm.

[0048] The thickness of the back electrode layer is 10-220 nm; for example, the thickness of the back electrode layer is 30-200 nm.

[0049] Specifically, the thickness of the back electrode layer is the total thickness of the MoN layer, Al layer, and Cr layer, or the total thickness of the Ag layer, NiCr layer, and Al layer.

[0050] The activation method for the absorption layer is as follows: S1. After the cadmium telluride absorber layer is plated, it is first cleaned with a cleaning machine before proceeding with the spraying process. The spraying solution is a CdCl2 concentration of 30g / 100ml, with the addition of tellurium tetrachloride and cadmium perchlorate hexahydrate. The molar ratio of tellurium tetrachloride to cadmium perchlorate hexahydrate is 1:1, and the concentration is 0.03mol / L.

[0051] S2. After the solution is sprayed onto the chip surface, it is baked at 80°C for 5 minutes to evaporate the moisture, leaving a mixture of cadmium chloride and tellurium dioxide on the chip. After removing the coating on the reverse side of the chip with acid, it enters the vacuum activation chamber.

[0052] The vacuum chamber is evacuated to a vacuum level of 1.0 Pa, the substrate is heated to 420°C, and an Ar / H2 mixed gas (Ar:H2 = 99:1) is introduced at a flow rate of 1500 sccm for 30 minutes. This process improves grain size and simultaneously forms a tellurium-rich layer. No acid pickling is performed after this step.

[0053] Then the next step is to plate the back contact layer, until the chip processing is complete.

[0054] Comparative Example 1 This comparative example provides a cadmium telluride thin-film solar cell, the structure of which consists of a transparent substrate, a front electrode layer, a window layer, an absorber layer, a back contact layer, and a back electrode layer arranged sequentially, the same as in Example 1, except for the activation of the absorber layer, wherein the activation method of the absorber layer is as follows: S1. After the cadmium telluride absorber layer is plated, it is first cleaned with a cleaning machine before proceeding with the spraying process. The spraying solution is CdCl2 with a concentration of 30g / 100ml.

[0055] S2. After the solution is sprayed onto the chip surface, it is baked at 80°C for 5 minutes to evaporate the moisture, leaving cadmium chloride on the chip. It is then activated in a tunnel furnace, where the substrate is heated to 420°C for 30 minutes to improve the grain size. Afterward, the coating on the back of the chip is removed with acid, and then surface pickling is used to remove cadmium chloride particles and oxides from the surface and form a tellurium-rich layer.

[0056] Then the next step is to plate the back contact layer, until the chip processing is complete.

[0057] Absorption layer characterization Figure 1 This is a scanning electron microscope (SEM) image of the cadmium telluride absorption layer in Example 1; Figure 3The image shows a scanning electron microscope (SEM) image of the cadmium telluride absorbing layer of Comparative Example 1. The grain size of the cadmium telluride absorbing layer of Comparative Example 1 is basically between 2 and 4 micrometers, and there are many pores. In contrast, the grain size of the cadmium telluride absorbing layer of Example 1 reaches more than 5 micrometers, and there are no pores on the grain surface.

[0058] Figure 2 EDS energy dispersive spectroscopy analysis of the cadmium telluride absorption layer in Example 1; Figure 4 The following is an EDS energy dispersive spectroscopy analysis of the cadmium telluride absorbing layer of Comparative Example 1; the energy dispersive spectral data of Example 1 and Comparative Example 1 are shown in Tables 1 and 2 below: Table 1. EDS energy dispersive spectral data of the cadmium telluride absorber layer in Example 1

[0059] Table 2. EDS energy dispersive spectral data of the cadmium telluride absorber layer in Comparative Example 1

[0060] As shown in the EDS energy dispersive spectroscopy analysis in Table 1, no residual chlorine atoms were detected in the cadmium telluride absorption layer of Example 1, and the atomic percentage of tellurium was slightly higher than that of cadmium, indicating that a tellurium-rich layer was formed on the crystal surface. However, the EDS energy dispersive spectroscopy analysis in Table 2 detected chlorine, and the atomic percentage of cadmium was higher than that of tellurium, indicating that cadmium chloride residue was present on the surface after acid washing, resulting in crystal defects with pores, and the grain size of 2-4 micrometers was relatively small.

[0061] Performance testing of cadmium telluride thin-film solar cells Performance tests were conducted on the cadmium telluride thin-film solar cells of Example 1 and Comparative Example 1. The test method used an IV meter; different voltages were applied to the positive and negative electrodes of the chip to measure the IU and PU curves. The software automatically calculated parameters such as Voc, Isc, and Pmax, and calculated the power generation efficiency based on the input chip area. The power generation efficiency data after photo-activated illumination were compared, and the initial efficiency, the power generation efficiency after 2 hours of illumination, and the power generation efficiency after 4 hours of illumination were statistically analyzed. Figure 5 As shown, the power generation efficiency of the cadmium telluride thin-film solar cell in Example 1 after 4 hours of illumination was 18.5%, while the power generation efficiency of the cadmium telluride thin-film solar cell in Comparative Example 1 after 4 hours of illumination was 17.5%.

[0062] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An activating solution for activating cadmium telluride thin films, characterized in that, It includes the following components: cadmium chloride, tellurium tetrachloride, cadmium perchlorate or its hydrate, and water.

2. The activating solution for activating cadmium telluride thin films according to claim 1, characterized in that, The concentrations of each component in the activation solution satisfy at least one of the following conditions: A) The concentration of cadmium chloride is 50-1000 g / L; B) The concentration of tellurium tetrachloride is 0.01-0.1 mol / L; C) The concentration of cadmium perchlorate or its hydrate is 0.01-0.1 mol / L.

3. The application of the activating solution for activating cadmium telluride thin films as described in claim 1 or 2 in the preparation of cadmium telluride thin-film solar cells.

4. A method for preparing a cadmium telluride thin-film solar cell, characterized in that, The cadmium telluride thin-film solar cell includes a cadmium telluride absorber layer, and the preparation method includes the following steps: coating the surface of the cadmium telluride absorber layer with the activation solution described in claim 1 or 2, drying the activation solution, and performing annealing heat treatment to activate the cadmium telluride absorber layer.

5. The method for preparing a cadmium telluride thin-film solar cell according to claim 4, characterized in that, The annealing heat treatment includes the following steps: placing the cadmium telluride absorber layer in a vacuum activation chamber, filling it with an Ar / H2 mixed gas, and performing annealing heat treatment.

6. The method for preparing a cadmium telluride thin-film solar cell according to claim 5, characterized in that, The vacuum degree of the vacuum activation chamber is 0.1-1.0 Pa; And / or, the volume percentage of Ar gas in the Ar / H2 mixture is 99%-99.9%.

7. The method for preparing cadmium telluride thin-film solar cells according to claim 4, characterized in that, The annealing heat treatment temperature is 350-450℃.

8. The method for preparing a cadmium telluride thin-film solar cell according to claim 4, characterized in that, The cadmium telluride thin-film solar cell comprises a substrate, a front electrode, a window layer, an absorber layer, a back contact layer, and a back electrode metal layer arranged sequentially.

9. The method for preparing a cadmium telluride thin-film solar cell according to claim 8, characterized in that, After the activation process is completed, a back contact layer is plated on the surface of the cadmium telluride absorber layer.

10. A cadmium telluride thin-film solar cell prepared by the method according to any one of claims 4-9.

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