Layered continuous recovery method for heterojunction solar cells
Through the heterojunction solar cell stratified continuous recovery method, the problems of low recycling efficiency and high cost of waste heterojunction solar cells are solved by using steps such as nitric acid solution, indium oxide reduction and alkali corrosion, and high efficiency of silver, indium and silicon recycling is achieved, which has the advantages of environmental protection and reducing carbon emissions.
Patent Information
- Application Number
- CN202411740498.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-03-14
AI Technical Summary
In the prior art, waste heterojunction solar cells have low recycling efficiency, high processing costs and complex operations, resulting in waste of silver, indium and silicon resources and environmental pollution.
The heterojunction solar cell stratified continuous recovery method is adopted, and the silver gate wire is removed by nitric acid solution treatment, and the high-temperature indium oxide is reduced to remove and recovered indium element, and the single crystal silicon is recovered by lye corrosion.
High-efficiency continuous separation and recovery of silver, indium and silicon are achieved, with silver recovery rate above 90%, indium recovery rate around 90%, silicon recovery rate above 95%, and purity above 99%, reducing processing costs and simplifying the process flow.
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Figure CN119614885A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of recycling waste solar cells, and in particular to a method for continuous recycling of heterojunction solar cells by stratification. Background Art
[0002] Generally speaking, the life of a photovoltaic module is about 25 years. In addition to recyclable materials such as glass and aluminum, photovoltaic modules also contain rare metals such as silver, gallium, and indium. If photovoltaic modules are not recycled after they are scrapped, it will cause great pollution to the ecological environment.
[0003] Optimizing the recycling of silicon, silver and indium in waste heterojunction solar cells, reducing the impact of manufacturing emissions on the environment, reducing production or processing costs, and keeping toxic electronic waste away from landfills are the trends in the development of the photovoltaic market. In waste heterojunction solar cells, monocrystalline silicon accounts for more than 90%, silver accounts for about 3% to 4%, and indium accounts for about 0.2% to 0.4%. Indium is located in the transparent conductive film layer (TCO) under the silver grid line. The main component of this conductive film layer is indium tin oxide deposition material; indium is a widely used but scarce metal with an expensive price. Indium and its compounds can be used in electronic, infrared and optical devices; if indium is not properly handled, it will not only waste resources but also cause environmental pollution. It can be seen that if silver, indium and silicon can be recycled efficiently and at low cost, it will bring greater benefits to enterprises.
[0004] At present, the method of recycling waste solar cells not only has the problems of low silver recovery efficiency and poor purity, but also cannot subsequently recover indium alone, resulting in a waste of indium resources. At the same time, the purity of the recycled silicon material is low and the processing cost is high.
[0005] Therefore, for waste heterojunction solar cells, it is urgent to develop a recycling method with high recycling efficiency, low processing cost and simple process, so as to improve enterprise benefits. Summary of the invention
[0006] One of the purposes of the present invention is to provide a method for continuous layered recycling of heterojunction solar cells, which can not only effectively and gradually separate and recover valuable materials from waste heterojunction solar cells, achieving the purpose of high-efficiency continuous separation of silver, indium and silicon, but also the recycling method is easy to operate, low in cost, easy to industrialize, and also environmentally friendly.
[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:
[0008] A method for continuous recycling of heterojunction solar cells by delamination, comprising the following steps:
[0009] S1: waste heterojunction solar cells are treated with a nitric acid solution to remove the silver grid lines, thereby obtaining desilvered solar cells and a silver nitrate solution;
[0010] reacting the silver nitrate solution with an alkaline solution to obtain a silver oxide precipitate, and thermally decomposing the silver oxide precipitate to obtain a silver element;
[0011] S2: Reducing and removing the indium oxide in the conductive film layer on the desilvered battery cell to obtain an indium-free battery cell and an indium element;
[0012] S3: placing the de-indiumized cell in an alkaline solution to completely corrode the silicon-doped composite film layer on the de-indiumized cell to obtain a single crystal silicon wafer.
[0013] The present invention realizes the continuous separation, extraction and recovery of silver (Ag), indium (In) and silicon (Si) from the surface to the inside on a heterojunction solar cell, with high recovery efficiency, simple and easy operation process and low cost, which is beneficial to improving enterprise benefits and solves the technical problems of low recovery efficiency, high processing cost and complex operation of waste heterojunction solar cells in the prior art.
[0014] Further, the pH value of the nitric acid solution is between 1 and 4, the temperature of the nitric acid solution is 50° C.-70° C., and the treatment time of the nitric acid solution is 6 min-12 min;
[0015] The silver nitrate solution includes a supersaturated silver nitrate solution.
[0016] Furthermore, in step S1, the alkaline solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution, the pH value of the alkaline solution is between 12 and 14, and the thermal decomposition temperature of the silver oxide precipitate is 440° C. to 500° C.
[0017] Furthermore, the method for reducing and removing indium oxide comprises the following steps:
[0018] The desilvered battery cell is placed in a mixed gas atmosphere of hydrogen and inert gas to reduce and remove indium oxide in the conductive film layer, thereby obtaining an indium-free battery cell and an indium single substance.
[0019] Furthermore, the temperature for reducing and removing indium oxide is 400°C-500°C.
[0020] Furthermore, the molar amount of the hydrogen is at least 3 times that of indium oxide.
[0021] Furthermore, in step S3, the alkali solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution, and the pH value of the alkali solution is between 12 and 14.
[0022] Furthermore, the temperature condition of placing the indium-free battery cell in the alkaline solution is 50° C.-70° C.
[0023] Furthermore, after the etching, the step of cleaning the single crystal silicon is also included.
[0024] Furthermore, the cleaning method includes RCA cleaning.
[0025] The recycling process adopted in the prior art usually has the technical problems of low recycling efficiency, high processing cost and complicated operation. Compared with the recycling process of the prior art, the method for continuous layered recycling of heterojunction solar cells of the present invention has the following beneficial effects: the waste heterojunction solar cells are first separated from the silver grid lines by a nitric acid solution, and the separation effect is improved by the mutual conversion of the solid phase and the liquid phase. The silver grid lines printed on the front and back sides are all detached and converted into a solution form, thereby obtaining a desilvered solar cell, the silver recovery rate is above 90% and the purity is above 99%, and the exposed part after desilvering is a conductive film layer (the main component is an indium tin oxide deposition material), and then the indium oxide is reduced and removed at a high temperature to recover the indium element, and the indium recovery rate is above 90%. % and its purity is above 99%, and an indium-free solar cell is obtained, which consists of a flat single crystal silicon substrate and a deposited and covered amorphous silicon / polycrystalline silicon composite film layer structure destroyed by high temperature. Finally, the amorphous silicon / polycrystalline silicon composite film layer structure is completely corroded by alkali solution to recover single crystal silicon, and the silicon recovery rate is about 95% and its purity is above 99%. It can be seen that the recovery method of the present invention is simple and ingenious, not only can it effectively and gradually separate and recover valuable materials from waste heterojunction solar cells, the material recovery rate is high and the purity is good, and the purpose of efficiently and continuously separating silver, indium and silicon is achieved, and the recovery method is easy to operate, low in cost, easy to industrialize, and is conducive to improving enterprise benefits. At the same time, it is also environmentally friendly and has the advantages of environmental protection and reducing carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0027] Figure 1 A process flow chart of a method for continuous layered recovery of silver, indium and silicon from waste heterojunction solar cells provided in Example 1 of the present invention;
[0028] Figure 2 A schematic diagram of the structure of a heterojunction solar cell provided in Example 1 of the present invention;
[0029] Figure 3 A schematic diagram of the structure of a heterojunction solar cell provided in Example 1 of the present invention after the silver grid line is detached;
[0030] Figure 4 A schematic diagram of the structure of a heterojunction solar cell after the indium oxide is removed provided in Example 1 of the present invention;
[0031] Figure 5 This is a schematic diagram of the structure of the heterojunction solar cell provided in Example 1 of the present invention after the composite film layer is corroded. DETAILED DESCRIPTION
[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0033] The structure of a heterojunction solar cell consists of a silver (Ag) grid line, a conductive thin film layer (TCO), a composite film layer, and a single crystal silicon substrate from the outside to the inside.
[0034] The present invention provides a method for continuous recycling of heterojunction solar cells by delamination, comprising the following steps:
[0035] S1: waste heterojunction solar cells are treated with a nitric acid solution to remove the silver grid lines, thereby obtaining desilvered solar cells and a silver nitrate solution;
[0036] It should be noted that the appropriate pH value and temperature of the nitric acid solution must be ensured to fully separate the silver grid line; if the pH value of the nitric acid solution is too low or the temperature is too high, it is easy to cause safety risks and increase the processing (energy consumption) cost; if the pH value of the nitric acid solution is too high or the temperature is too low, it cannot fully separate the silver grid line;
[0037] The silver nitrate solution is reacted with an alkaline solution to obtain a silver oxide precipitate, and the silver oxide precipitate is thermally decomposed to obtain a silver element;
[0038] It should be noted that the appropriate pH value must be ensured so that the silver nitrate solution can fully generate silver oxide precipitation. If the pH value is too high or too low, the silver nitrate solution cannot fully generate silver oxide precipitation, which will reduce the recovery rate of silver element. At the same time, the appropriate thermal decomposition temperature must be ensured so that the silver oxide can be fully decomposed to obtain high-purity silver element. If the thermal decomposition temperature is too high or too low, the silver oxide cannot be fully decomposed, which will reduce the purity of the silver element.
[0039] S2: Reducing and removing the indium oxide in the conductive film layer on the desilvered battery cell to obtain an indium-free battery cell and an indium element;
[0040] It should be noted that an appropriate molar amount of hydrogen must be ensured so that indium oxide can be fully reduced in a hydrogen atmosphere to obtain indium element; if hydrogen is insufficient, indium oxide will generate low-valent oxides of indium; at the same time, an appropriate reduction temperature must be ensured so that indium oxide can be fully reduced to high-purity indium element; if the reduction temperature is too low, indium oxide cannot be reduced to indium element; if the reduction temperature is too high, by-products are easily generated during the reduction of indium oxide, which will reduce the purity of indium element;
[0041] S3: placing the de-indiumized cell in an alkaline solution to completely corrode the silicon-doped composite film layer on the de-indiumized cell to obtain a single crystal silicon wafer;
[0042] It should be noted that the appropriate pH value and corrosion temperature of the alkali solution must be ensured so that the composite film layer structure can be completely corroded to obtain a high-purity single crystal silicon substrate; if the pH value of the alkali solution is too low or the corrosion temperature is too low, the composite film layer structure cannot be corroded; if the pH value of the alkali solution is too high, it is easy to cause silicon damage; if the corrosion temperature is too high, it is easy to cause safety risks and energy waste.
[0043] The waste heterojunction solar cell is first separated from the silver grid line by a nitric acid solution, and the separation effect is improved by the mutual conversion of the solid phase and the liquid phase. The silver grid lines printed on the front and back sides are all detached and converted into a solution form. The obtained is a desilvered solar cell, and the silver recovery rate is more than 90% and the purity is more than 99%. The exposed part after desilvering is a conductive film layer (the main component is an indium tin oxide deposition material), and then the indium oxide is reduced and removed at a high temperature to recover the indium element, and the indium recovery rate is about 90% and the purity is more than 99%. At the same time, the de-indiumed solar cell is obtained, which consists of a flat single crystal silicon substrate and a deposited covered The amorphous silicon / polycrystalline silicon composite film layer structure is destroyed by high temperature, and finally the amorphous silicon / polycrystalline silicon composite film layer structure is completely corroded by alkali solution to recover single crystal silicon, and the silicon recovery rate is about 95% and the purity is above 99%; it can be seen that the recovery method of the present invention is simple and ingenious, not only can it effectively and gradually separate and recover valuable materials from waste heterojunction solar cells, the material recovery rate is high and the purity is good, and the purpose of high-efficiency and continuous separation of silver, indium and silicon is achieved, and the recovery method is easy to operate, low in cost, easy to industrialize, which is beneficial to improving enterprise benefits, and is also environmentally friendly, with the advantages of environmental protection and reducing carbon emissions.
[0044] In the present invention, the method for continuous recycling of heterojunction solar cells by delamination comprises the following steps:
[0045] (a) silver elements contained in silver grid lines in waste heterojunction solar cells are precipitated by nitric acid solution, separated from the silver grid lines, and a desilvered solar cell and a silver nitrate solution are obtained;
[0046] Silver element is precipitated through nitric acid solution, and the following chemical reactions mainly occur:
[0047] Ag+2HNO3(concentrated)=AgNO3+H2O+NO2↑;
[0048] 3Ag+4HNO3(dilute)=3AgNO3+2H2O+NO↑;
[0049] The silver nitrate solution is reacted with an alkaline solution to obtain a silver oxide precipitate, and the silver oxide precipitate is thermally decomposed in an inert gas atmosphere to obtain a silver element;
[0050] Silver nitrate undergoes the following chemical reaction:
[0051] 2AgNO3+2NaOH=Ag2O↓+H2O+2NaNO3;
[0052] Or, 2AgNO3+2KOH=Ag2O↓+H2O+2KNO3;
[0053] Silver oxide undergoes the following chemical reaction:
[0054] 2Ag2O=4Ag+O2↑(thermal decomposition in inert atmosphere);
[0055] In the above steps, the present invention selectively extracts and recovers high-purity silver (Ag) from waste solar cells using a three-step method (solid phase-liquid phase-solid phase);
[0056] It should be noted that when the silver element is selectively etched by the nitric acid solution, a large amount of organic components of the resin material contained in the silver paste grid lines of the heterojunction solar cell will also be corroded by the nitric acid solution and dissolved in the mixed solution system whose main components are nitric acid / silver nitrate. At this time, for the single solar cell, the silver grid lines printed on both the front and back sides have all fallen off and converted into solution form;
[0057] (b) placing the desilvered battery cell in step (a) in a mixed gas atmosphere of hydrogen and inert gas to reduce and remove indium oxide in the conductive film layer, thereby obtaining a desilvered battery cell and indium element;
[0058] In this step, indium (In) is extracted in an excess H2 atmosphere under high temperature conditions to remove the TCO transparent conductive film layer;
[0059] It should be noted that the silver grid lines on the battery have been detached in step (a), and the remaining exposed part is a conductive film layer (TCO), the main component of which is an indium tin oxide deposition material, which is placed in a mixed gas atmosphere of excess hydrogen (H2) and an inert gas, and indium oxide is thermally reduced in the presence of excess hydrogen or other reducing agents, thereby obtaining indium metal powder;
[0060] Indium oxide undergoes the following chemical reaction:
[0061] In2O3+3H2=2In+3H2O (excess hydrogen);
[0062] It should be noted that if there is insufficient hydrogen, indium oxide will generate low-valent oxides of indium, and the reaction is In2O3+2H2=In2O+2H2O (too little hydrogen); while In2O is easily oxidized in the air to generate indium oxide, and the reaction is In2O+O2=In2O3;
[0063] (c) placing the indium-removed cell in step (b) in an alkaline solution to completely corrode the composite film layer of amorphous silicon and polycrystalline silicon, and then cleaning the cell to obtain single crystal silicon;
[0064] It should be noted that in step (b), the indium metal has been recovered, and the remaining part is a planar single crystal silicon substrate and an amorphous silicon / polycrystalline silicon composite film layer structure deposited and covered thereon and damaged by high temperature (the hydrogen amorphous silicon film deposited by PECVD technology will be damaged at high temperature, hydrogen will escape, and part of the amorphous silicon will be converted into a polycrystalline structure due to the high temperature);
[0065] Therefore, in this step, the planar single crystal silicon substrate covered with amorphous silicon / polycrystalline silicon deposition is placed in an alkaline solution, so that the amorphous silicon / polycrystalline silicon composite film layer structure is completely corroded by the alkaline solution, thereby recovering a high-purity single crystal silicon substrate.
[0066] In summary, the present invention adopts a layered chemical separation and metal precipitation treatment method to achieve continuous separation, extraction and recovery of silver (Ag), indium (In) and silicon (Si) from the surface to the inside of waste heterojunction solar cells. The recovery rates of silver, indium and silicon can all reach more than 90% and the purities are all more than 99%. Not only is the recovery efficiency high, but the process is simple and easy to operate, and the cost is low, which is beneficial to improving the benefits of the enterprise and solves the technical problems of low recovery efficiency, high processing cost and complex operation of waste heterojunction solar cells in the prior art.
[0067] In a preferred embodiment, the pH value of the nitric acid solution used in the present invention can be between 1 and 4, and the temperature of the nitric acid solution can be between 50°C and 70°C. Typical but non-limiting temperatures are, for example, 50°C, 55°C, 60°C, 65°C, and 70°C. The appropriate pH value and temperature of the nitric acid solution are more conducive to fully detaching from the silver grid lines; if the pH value of the nitric acid solution is too low or the temperature is too high, it is easy to cause safety risks and increase processing (energy consumption) costs; if the pH value of the nitric acid solution is too high or the temperature is too low, it is difficult to fully detach from the silver grid lines.
[0068] The time for nitric acid solution treatment can be 6min-12min, and its typical but non-limiting time is, for example, 6min, 8min, 10min, and 12min. The appropriate treatment time of nitric acid solution is more conducive to fully detaching from the silver grid line, and is also conducive to ensuring the recycling efficiency; if the treatment time of nitric acid solution is too short, it is difficult to fully detach from the silver grid line; if the treatment time of nitric acid solution is too long, it is not conducive to improving the recycling efficiency.
[0069] In the present invention, the silver nitrate solution obtained by precipitation of silver element may be a supersaturated silver nitrate solution.
[0070] In a preferred embodiment, the alkaline solution reacting with the silver nitrate solution includes but is not limited to at least one of a sodium hydroxide solution and a potassium hydroxide solution. The pH value of the alkaline solution can be between 12 and 14. This pH value condition is the optimal reaction condition for the silver nitrate solution to generate a silver oxide precipitate, and is therefore more conducive to improving the generation effect of the silver oxide precipitate.
[0071] In a preferred embodiment, the temperature of thermal decomposition of silver oxide precipitate is 440°C-500°C, and typical but non-limiting temperatures are, for example, 440°C, 460°C, 480°C, and 500°C. This temperature condition is the optimal reaction condition for thermal decomposition of silver oxide precipitate, and is therefore more conducive to ensuring that the silver oxide precipitate is fully decomposed to generate silver element.
[0072] In a preferred embodiment, the temperature for reducing and removing indium oxide is 400°C-500°C, and typical but non-limiting temperatures are, for example, 400°C, 420°C, 440°C, 460°C, 480°C, and 500°C. This temperature condition is the optimal reaction condition for indium oxide to react with hydrogen and be reduced to indium element. At the same time, the molar amount of hydrogen is at least 3 times that of indium oxide, which can ensure that indium oxide is fully reduced in a hydrogen atmosphere to obtain indium element. If there is insufficient hydrogen, indium oxide will generate low-valent oxides of indium.
[0073] In a preferred embodiment, the alkaline solution for corroding the amorphous silicon / polycrystalline silicon composite film layer includes but is not limited to at least one of a sodium hydroxide solution and a potassium hydroxide solution. The pH value of the alkaline solution can be between 12 and 14, and the temperature conditions for corrosion can be 50°C-70°C. Typical but non-restrictive temperature conditions are, for example, 50°C, 55°C, 60°C, 65°C, and 70°C, which are more conducive to further ensuring that the amorphous silicon / polycrystalline silicon composite film layer structure is completely corroded, thereby obtaining a high-purity single crystal silicon substrate; if the pH value of the alkaline solution is too low or the temperature conditions for corrosion are too low, it is not conducive to completely corroding the amorphous silicon / polycrystalline silicon composite film layer structure; if the pH value of the alkaline solution is too high, it is easy to cause silicon damage; if the temperature conditions for corrosion are too high, it is easy to cause safety risks and energy waste.
[0074] In the present invention, after etching the amorphous silicon / polycrystalline silicon composite film layer, the step of cleaning the single crystal silicon is also included; wherein the cleaning method includes but is not limited to RCA cleaning.
[0075] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.
[0076] Example 1
[0077] A method for continuous layered recovery of silver, indium and silicon from waste heterojunction solar cells, see Figure 1 , including the following steps:
[0078] Step 1: The silver element in the solar cell is recovered through a three-step process to obtain high-purity metallic silver:
[0079] (1) Selective separation of silver element (Ag):
[0080] Using nitric acid (HNO3) solution with a pH value of 1 to 4, the solution was heated to 60°C and the waste heterojunction solar cells (the structure of heterojunction solar cells is shown in the figure) were removed within 9 minutes. Figure 2 The structure is composed of silver (Ag) grid lines, conductive film layer (TCO), composite film layer and single crystal silicon substrate from the outside to the inside. The silver element in the grid lines is selectively precipitated (the structure after the silver grid lines are separated is shown in Fig. Figure 3 ), the silver element becomes an ion form, thereby obtaining a desilvered battery cell and a supersaturated silver nitrate (AgNO3) solution;
[0081] When the silver element is selectively etched by nitric acid (HNO3) solution, the organic components of a large amount of resin materials contained in the silver paste grid lines in the heterojunction solar cell will also be corroded by the nitric acid solution and dissolved in the mixed solution system whose main components are nitric acid / silver nitrate. At this time, for the single cell, the silver grid lines printed on both the front and back sides have all fallen off and converted into solution form;
[0082] (2) Silver nitrate (AgNO3) reacts to form silver oxide (Ag2O):
[0083] A sodium hydroxide (NaOH) solution (pH 13) is poured into the supersaturated silver nitrate (AgNO3) solution obtained in step (1). Under normal temperature conditions, AgNO3 and NaOH react rapidly to generate silver oxide (Ag2O) precipitate, which eventually accumulates at the bottom of the reaction device;
[0084] (3) Extraction of high-purity silver (Ag) from silver oxide (Ag2O):
[0085] The silver oxide (Ag2O) precipitate obtained in step (2) is collected and heated to 470° C. in an inert gas atmosphere, whereby the silver oxide (Ag2O) is thermally decomposed to obtain high-purity silver (Ag), wherein the silver recovery rate is above 90% and the purity is above 99%;
[0086] Step 2: Recycling of indium elements in solar cells to obtain metallic indium:
[0087] In the first step, the silver grid lines on the battery have been removed, and the desilvered battery cell obtained has a conductive film layer exposed in the portion mainly composed of indium tin oxide deposition material. The desilvered battery cell is placed in a mixed gas atmosphere of excess hydrogen and inert gas. Indium oxide (In2O3) is heated to 450°C in the presence of excess hydrogen (H2) and a reducing agent to remove indium oxide (the structure of indium oxide after removal is shown in FIG. Figure 4 ), thereby reducing to obtain indium (In) metal powder, i.e., indium element, with an indium recovery rate of about 90% and a purity of more than 99%, and obtaining an indium-free battery cell;
[0088] Step 3: Recovery of high-purity monocrystalline silicon in solar cells:
[0089] In the second step, the indium metal in the film is recovered, and the obtained indium-free cell is a planar single-crystal silicon substrate and an amorphous silicon / polycrystalline silicon composite film layer structure that is damaged by high temperature deposited thereon (the hydrogen amorphous silicon film deposited by PECVD technology will be damaged at high temperature, hydrogen will escape, and part of the amorphous silicon will be converted into a polycrystalline structure due to high temperature);
[0090] The de-indiumized cell was placed in a potassium hydroxide (KOH) solution with a pH value of 13 and heated to 60°C. The amorphous silicon / polycrystalline silicon composite film structure was completely corroded within 2 minutes (the structure of the composite film after corrosion is shown in Figure 2). Figure 5 ), followed by a standard RCA cleaning process to recover the high-purity single-crystalline silicon substrate to obtain high-purity single-crystalline silicon (Si), with a silicon recovery rate of about 95% and a purity of more than 99%.
[0091] Example 2
[0092] The difference between this embodiment and embodiment 1 is that, when silver element (Ag) is selectively precipitated and separated, the nitric acid solution is heated to 50° C. in this embodiment, and the time for selective precipitation of silver element is 12 minutes;
[0093] The remaining steps and process parameters are the same as those in Example 1;
[0094] The recovery rates and purities of silver, indium and silicon can basically achieve the same recovery effect as that of Example 1.
[0095] Example 3
[0096] The difference between this embodiment and embodiment 1 is that, when silver element (Ag) is selectively precipitated and separated, the nitric acid solution is heated to 70° C. in this embodiment, and the time for selective precipitation of silver element is 6 minutes;
[0097] The remaining steps and process parameters are the same as those in Example 1;
[0098] The recovery rates and purities of silver, indium and silicon can basically achieve the same recovery effect as that of Example 1.
[0099] Example 4
[0100] The difference between this embodiment and embodiment 1 is that when reducing indium oxide (In2O3) in the second step, this embodiment performs the reduction at a temperature of 400°C;
[0101] The remaining steps and process parameters are the same as those in Example 1;
[0102] The recovery rates and purities of silver, indium and silicon can basically achieve the same recovery effect as that of Example 1.
[0103] Example 5
[0104] The difference between this embodiment and embodiment 1 is that when reducing indium oxide (In2O3) in the second step, this embodiment performs the reduction at a temperature of 500°C;
[0105] The remaining steps and process parameters are the same as those in Example 1;
[0106] The recovery rates and purities of silver, indium and silicon can basically achieve the same recovery effect as that of Example 1.
[0107] Example 6
[0108] The difference between this embodiment and embodiment 1 is that, when etching the amorphous silicon / polycrystalline silicon composite film structure in the third step, this embodiment uses a sodium hydroxide (NaOH) solution with a pH value of 13;
[0109] The remaining steps and process parameters are the same as those in Example 1;
[0110] The recovery rates and purities of silver, indium and silicon can basically achieve the same recovery effect as that of Example 1.
[0111] It can be seen that the layered continuous recovery method of the present invention realizes the continuous separation, extraction and recovery of silver (Ag), indium (In) and silicon (Si) from the surface to the inside of the waste heterojunction solar cell, and the recovery rates of silver, indium and silicon can reach more than 90% and the purity is more than 99%. Compared with the prior art, it not only effectively recovers indium resources and avoids the waste of indium resources, but also improves the purity of the recovered silicon and the recovery rate of silver.
[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for continuous recycling of heterojunction solar cells by stratification, characterized in that: The following steps are involved: S1: treating the waste heterojunction solar cell with a nitric acid solution to remove the silver grid lines, thereby obtaining a desilvered solar cell and a silver nitrate solution; reacting the silver nitrate solution with an alkaline solution to obtain a silver oxide precipitate, and thermally decomposing the silver oxide precipitate to obtain a silver element; S2: Reducing and removing the indium oxide in the conductive film layer on the desilvered battery cell to obtain an indium-free battery cell and an indium element; S3: placing the de-indiumized cell in an alkaline solution to completely corrode the silicon-doped composite film layer on the de-indiumized cell to obtain a single crystal silicon wafer.
2. The method for continuous layered recovery according to claim 1, characterized in that: The pH value of the nitric acid solution is between 1 and 4, the temperature of the nitric acid solution is between 50° C. and 70° C., and the treatment time of the nitric acid solution is between 6 and 12 minutes; The silver nitrate solution includes a saturated silver nitrate solution.
3. The method for continuous layered recovery according to claim 1, characterized in that: In step S1, the alkaline solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution, the pH value of the alkaline solution is between 12 and 14, and the thermal decomposition temperature of the silver oxide precipitate is 440° C. to 500° C.
4. The method for continuous layered recovery according to claim 1, characterized in that: The method for reducing and removing indium oxide comprises the following steps: The desilvered battery cell is placed in a mixed gas atmosphere of hydrogen and inert gas to reduce and remove the indium oxide in the conductive film layer, thereby obtaining the desilvered battery cell and indium element.
5. The method for continuous layered recovery according to claim 4, characterized in that: The temperature for reducing and removing indium oxide is 400°C-500°C.
6. The method for continuous layered recovery according to claim 4, characterized in that: The molar amount of the hydrogen is at least 3 times that of indium oxide.
7. The method for continuous layered recovery according to claim 1, characterized in that: In step S3, the alkali solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution, and the pH value of the alkali solution is between 12 and 14.
8. The method for continuous layered recovery according to claim 1, characterized in that: The temperature condition of placing the indium-free battery sheet in the alkaline solution is 50° C.-70° C.
9. The method for continuous layered recovery according to claim 1, characterized in that: The method further includes a step of cleaning the single crystal silicon after the etching.
10. The method for continuous layered recovery according to claim 9, characterized in that: The cleaning method includes RCA cleaning.