JP2006093336A - Method for taking out solar cell substrate material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of taking out a silicon substrate material from among the crystalline silicon system solar cell modules recognized as defective products in a state that they are in used or enclosed into EVA in a manufacturing process. <P>SOLUTION: A solar cell module 10 is constituted by laminating a photovoltaic cell 1 surrounded by EVA2 and light receiving surface glass 4. It is exposed to a supercritical atmosphere or a subcritical atmosphere so as to decompose the EVA2. The supercritical atmosphere or the subcritical atmosphere is obtained by using water, a carbon dioxide, methanol, an ethanol or acetic acid as a medium. Thus, a substrate material 11 in the photovoltaic cell 1 is taken out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for taking out a solar cell substrate material from solar cells.

  In recent years, solar power generation systems have been attracting attention rapidly due to environmental conservation problems, and the amount of introduction has been increasing year by year, including those for general housing. On the other hand, about 10 years have passed since the introduction of solar cell subsidies for residential buildings in Japan, and in the future, installed solar cell modules will be used up by dubbing roofs, rebuilding houses, etc., and discarded. There is a possibility that it will be disposed of.

  At present, after the solar cell module separates metal parts by heat treatment, the residual slag is disposed as a cement material, and the silicon substrate material is hardly recycled at present.

  In other words, the silicon substrate material in the silicon-based solar cell module is tightly sealed with, for example, EVA (ethylene vinyl acetate), which is a heat-crosslinkable transparent resin, and is protected so as to be hardly affected by the outside air. It has a structure. Therefore, it is difficult to take out the silicon substrate material enclosed in EVA, and since no method has been found for taking out the silicon substrate material of the solar cell module at present, the silicon substrate material has not been recycled.

As a method of reusing silicon that has been conventionally discarded, there has been proposed a method in which silicon sludge is dissolved and solidified to be processed again into a high-purity silicon ingot (see, for example, Patent Documents 1 and 2). However, these methods require a great deal of energy and labor, and there is a problem that they are not realistic at this stage.
JP-A-9-165212 Japanese Patent Laid-Open No. 10-120493

  As described above, when disposing of the solar cell module, it is difficult to take out the silicon substrate material enclosed in the EVA, so that the silicon substrate material that has not yet lost its power generation capability and is valuable. The current situation is that they are also discarded.

  Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a solar cell for taking out and recycling a silicon substrate material in a crystalline silicon-based solar cell module that has been conventionally disposed of. An object of the present invention is to provide a method for taking out a substrate material. That is, the present invention provides a method for taking out a silicon substrate material in a crystalline silicon solar cell module that has been used or is in the middle of a manufacturing process (specifically, a defective product is encapsulated in EVA).

  In order to achieve the above-described object, a method for taking out a solar cell substrate material according to the present invention includes a substrate material in a solar cell from a solar cell module in which a solar cell surrounded by EVA and a learning surface glass are laminated. The solar cell module is exposed to a supercritical atmosphere or a subcritical atmosphere, and the EVA is decomposed to take out the substrate material in the solar cell.

  According to such an invention, the solar cell can be easily taken out by decomposing and removing EVA in a supercritical atmosphere or a subcritical atmosphere, and silicon is removed from the solar cell in a reusable state. The substrate material can be removed.

  Further, the present invention is characterized in that the supercritical atmosphere or subcritical atmosphere uses water, carbon dioxide, methanol, ethanol, or acetic acid as a medium.

  In the above invention, the supercritical atmosphere or subcritical atmosphere using water as a medium is preferably set such that the temperature is in the range of 374.2 ± 100 ° C. and the atmospheric pressure is in the range of 22.1 ± 10 MPa. . This is because the supercritical point of water is about 374 ° C. and the pressure is about 22 MPa. Further, by forming subcritical conditions for lowering the temperature and pressure in the vicinity of the supercritical point, the load due to the temperature and pressure on the solar cells enclosed in the solar cell module can be reduced and processed.

  In addition, when water is used as a medium in a supercritical atmosphere or a subcritical atmosphere as described above, an acid solution or an alkali solution may be added to the water. Thereby, the effect of relieving the decomposition of EVA or the adhesion between the EVA and the glass interface can be expected. That is, the EVA decomposition reaction can be promoted.

  In the above invention, the supercritical atmosphere or subcritical atmosphere using methanol as a medium is preferably set such that the temperature is in the range of 239.9 ± 100 ° C. and the atmospheric pressure is in the range of 8.1 ± 5 MPa. . This is because the supercritical point of methanol is about 240 ° C. and the pressure is about 8.1 MPa. Further, by forming subcritical conditions for lowering the temperature and pressure in the vicinity of the supercritical point, the load due to the temperature and pressure on the solar cells enclosed in the solar cell module can be reduced and processed.

  In the above invention, the supercritical or subcritical atmosphere using ethanol as a medium has a temperature in the range of 242.2 ± 100 ° C. and the atmospheric pressure in the range of 6.36 ± 5 MPa. Is preferred. This is because the supercritical point of ethanol is about 242 ° C. and the pressure is about 6.3 MPa. Further, by forming subcritical conditions for lowering the temperature and pressure in the vicinity of the supercritical point, the load due to the temperature and pressure on the solar cells enclosed in the solar cell module can be reduced and processed.

  In the invention, the supercritical atmosphere or subcritical atmosphere using carbon dioxide as a medium has a temperature in the range of −10 ° C. to + 100 ° C. with respect to the supercritical temperature of 31.1 ° C., and the atmospheric pressure is 7 It is preferably set within the range of 39 ± 5 MPa. This is because the supercritical point of carbon dioxide is about 31 ° C. and the pressure is about 7.4 MPa. By reducing the temperature and pressure in the vicinity of the supercritical point, the load due to the temperature and pressure on the solar cells enclosed in the solar cell module can be reduced and processed. However, when carbon dioxide is used as a medium, the supercritical temperature is relatively low at about 31.1 ° C., and there is no influence on the solar battery cells enclosed in the solar battery module. In order to promote this, it is possible to perform the treatment in an atmosphere within a range of about −10 ° C. (21.1 ° C.) on the lower temperature side than the supercritical temperature and + 100 ° C. (131.1 ° C.) on the higher temperature side.

  In the above invention, the supercritical atmosphere or subcritical atmosphere using acetic acid as a medium has a temperature within a range of 321.4 ± 100 ° C. and an atmospheric pressure within a range of 5.79 ± 3 MPa. Is preferred. This is because the supercritical point of acetic acid is about 321 ° C. and the pressure is about 5.8 MPa. Further, by forming subcritical conditions for lowering the temperature and pressure in the vicinity of the supercritical point, the load due to the temperature and pressure on the solar cells enclosed in the solar cell module can be reduced and processed.

  Furthermore, in the step of decomposing / removing the EVA, in order not to cause cracking or the like in the solar battery cell, the time until the atmosphere reaches a predetermined temperature is 5 minutes or more, and after maintaining the temperature, The time until the temperature is lowered to room temperature is preferably 5 minutes or more. That is, a sudden temperature change in which the temperature rise time and the temperature fall time are 5 minutes or less may cause cracking in the solar battery cell. A more preferable temperature increase time is about 2 ° C./min in terms of the temperature increase rate, and a more preferable temperature decrease time is about 4 ° C./min in terms of the temperature decrease rate. The temperature raising time and temperature falling time may be about 2 hours at the longest. This is because there is no difference in the occurrence of cracks or the like of the solar battery cells over 2 hours or more.

  In addition, before the solar cell module is put into a supercritical atmosphere or a subcritical atmosphere, a chemical immersion treatment such as nitric acid, sodium hydroxide, or trichloroethylene may be performed. According to this, since the main chain of the ethylene unit and the vinyl acetate unit, which is the basic structure of EVA, is broken, the decomposition start temperature of EVA is lowered, and EVA is applied to the adhesive force or cell that confines the solar cell. The pressure etc. which are can be relieved. Therefore, even if the solar cell module is subsequently placed in a supercritical atmosphere or a subcritical atmosphere, it is possible to prevent damage such as cracks from occurring in the solar cells.

  According to the method for taking out a solar cell substrate material of the present invention configured as described above, a reusable solar cell substrate material (that is, a crystalline silicon-based solar cell module) (i.e., a crystalline silicon solar cell module) is used. , Silicon substrate material) can be taken out. Moreover, the taken-out silicon substrate material can be reused for new solar cells as a silicon wafer for solar cells. Furthermore, the taken-out silicon substrate material can be melted, solidified, and processed again into a high-purity solar cell silicon ingot.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a crystalline silicon-based solar cell module which is an example of a solar cell module recycled by the method for taking out a solar cell substrate material according to the present invention.

  This solar cell module 10 prevents the front cover 4 from which incident light can be taken in and the back surface of the solar cell 1 being directly exposed to the outside air in a state where the solar cell 1 is sandwiched between EVA 2 which is a crosslinkable transparent adhesive resin. Therefore, the back cover 3 is laminated. Further, the peripheral portion is fixed by an aluminum frame 6 for installation on a gantry or the like (not shown), and a terminal box 5 for taking out the output of each solar cell 1 is attached to the back cover 3.

  In the present invention, first, in order to take out the solar cell 1 of the solar cell module 10, the terminal box 5 and the frame 6 of the solar cell module 10 are removed by a mechanical method (first step). Through this process, the module 20 in the middle of disassembly shown in FIG. 2 is obtained. The module 20 in the middle of disassembly includes the EVA 2 in which the solar cells 1 are enclosed, the back cover 3 and the front cover 4.

  Next, it is preferable to immerse the module 20 in the middle of disassembly in a chemical solution such as a nitric acid solution, a sodium hydroxide solution, or trichloroethylene (second step). Specifically, as shown in FIG. 3, any one of these chemical solutions 60 is put into a container 50, the module 20 in the middle of disassembly is put into the container 50, and the chemical solution 60 is immersed, and the state is maintained for a certain period of time. To do.

  For example, when a nitric acid solution is used as the chemical solution 60, the minimum concentration for accelerating the reaction is 0.1% by weight, so the concentration of the nitric acid solution is preferably 0.1% by weight or more. In addition, if the immersion time is short, the decomposition reaction of EVA2 is not promoted, so at least 30 seconds or more is necessary. The temperature of the nitric acid solution may be normal temperature or higher than normal temperature, and specifically, preferably in the range of 5 ° C to 80 ° C. Thereby, EVA2 changes with the effect | action of the chemical | medical solution 60, the module 30 in the middle of a disassembly can be obtained, and the ratio which the photovoltaic cell 1 cracks in a subsequent process can be reduced significantly.

  Next, after the module 30 in the middle of disassembly is sufficiently washed with pure water, it is put into a reaction furnace 80 as shown in FIG. 4 (third step). The reactor 80 is configured to control temperature and pressure, and can create a supercritical or subcritical atmosphere. This supercritical or subcritical atmosphere is formed using water, carbon dioxide, methanol, ethanol, or acetic acid as a medium. Then, the temperature and pressure in the reaction furnace 80 are adjusted to a predetermined level for each medium, and a predetermined atmosphere holding time is secured so as to obtain a sufficient reaction, thereby promoting the decomposition of EVA2. The atmosphere holding time is required to be at least 5 minutes. EVA2 is decomposed by holding for 5 minutes or more. However, the heating and holding time may be determined according to the state in which EVA2 is decomposed.

  Thereby, in the module 30 exposed in the supercritical or subcritical atmosphere, the laminated back cover 3 is hydrolyzed and powdered. Moreover, EVA2 enclosing the solar battery cell 1 can be decomposed into a jelly and removed. Furthermore, as shown in FIG. 5, the front cover 4 and the EVA 2 can be peeled off.

  After the EVA 2 is decomposed and removed in this way, the atmospheric temperature in the reaction furnace 80 is gradually lowered to room temperature over a period of 5 minutes or more. This is because an abrupt temperature change can cause a crack in the solar battery cell. Similarly, when raising the atmospheric temperature of the reaction furnace 80, it is preferable to gradually carry out over 5 minutes.

  However, when the temperature is lowered when the supercritical or subcritical atmosphere is dissolved, the EVA 2 is solidified again, and the solar battery cell 1 is again confined in the EVA 2. However, since EVA2 is once separated from solar cell 1 in a supercritical or subcritical atmosphere, after removing module 30 from the supercritical or subcritical atmosphere, solar cell 1 is removed from the resolidified EVA2. It is easy to take out. That is, for example, as shown in FIG. 6, the re-solidified EVA 2 can be easily taken out by mechanically cutting it off at the interface of the solar battery cell 1 (fourth step).

  During the above process, the solder material that is the cell electrode melts when exposed to a supercritical or subcritical atmospheric temperature above its melting point, and a part of the silver of the electrode material under the solder elutes. It is possible to end up. Such a point can be overcome by setting the supercritical or subcritical atmosphere temperature below the solder melting point with water or other media.

  Alternatively, if it is confirmed that the silver 13 resulting from the melting of the solder material has partially migrated to the silicon substrate material 11 in the extracted solar battery cell 1, the solar battery cell 1 is directly incorporated into a new solar battery module. Since it cannot be used, it is preferable to take out the silicon substrate material 11 in a reusable state. That is, by performing acid treatment or alkali treatment, the antireflection film 12, the silver electrode 13, and the solder 14 are removed from the solar battery cell 1, and impurities on the surface of the silicon substrate material 11 are migrated. And the silicon substrate material 11 is taken out.

  In this case, as shown in FIG. 7, the antireflection film 12, the silver electrode films 13 on the front and back surfaces, and the solder 14 are removed by hydrofluoric acid treatment. At this time, when the silver electrode film 13 contains a glass component, the removal becomes easier. Here, the treatment liquid used for the hydrofluoric acid treatment is preferably a treatment liquid containing 0.1 to 50% by weight of hydrofluoric acid. A more preferable hydrofluoric acid concentration is 1 to 10% by weight. The hydrofluoric acid treatment condition is preferably 5 to 80 ° C for 0.1 to 50 minutes, more preferably 10 to 40 ° C for 0.5 to 10 minutes. The hydrofluoric acid treatment is usually performed by dipping in a treatment solution.

  Next, the impurity layer is removed by a mixed solution treatment of nitric acid and hydrofluoric acid or a sodium hydroxide treatment. Here, when using a mixed solution of nitric acid and hydrofluoric acid, the ratio of nitric acid and hydrofluoric acid during the mixing treatment is preferably 0.1 to 50: 1, more preferably 2 to 20: 1. Is done. The ratio of the total amount of nitric acid and hydrofluoric acid to the mixed solution is preferably 0.1 to 100% by weight, and more preferably 1 to 50% by weight. The mixed solution treatment condition is preferably 5 to 80 ° C. for 0.1 to 50 minutes, more preferably 10 to 40 ° C. for 0.5 to 10 minutes. Also in this case, a method of immersing in a normal processing solution is employed.

  On the other hand, in the case of sodium hydroxide treatment, a treatment liquid containing 0.1 to 30% by weight of sodium hydroxide is preferable. A more preferable sodium hydroxide concentration is 1 to 10% by weight. Sodium hydroxide treatment conditions are preferably 5 to 90 ° C for 0.1 to 50 minutes, more preferably 60 to 90 ° C for 3 to 20 minutes. Also in this case, a method of immersing in a normal processing solution is employed.

  After completion of these treatments, treatment is performed by immersing in a mixed solution composed of hydrochloric acid and hydrogen peroxide solution to prevent oxidation of the surface of the silicon substrate material 11 and stabilize the surface, and then from ammonia water and hydrogen peroxide solution. It is preferable to neutralize the surface of the silicon substrate material 11 by immersing it in a mixed solution.

  The silicon substrate material 11 thus taken out can be reused for a new solar battery cell as a silicon wafer for a solar battery. Further, the silicon substrate material 11 can be melted and solidified, and processed again into a high-purity silicon ingot. Therefore, the solar battery cell 1 in the crystalline silicon solar battery module 10 can be recycled.

  In the case of a solar cell structure in which the solder is not dipped, the migration of the silver electrode due to melting of the solder does not occur in the silicon substrate material 11 and can be reused as a cell as it is.

  Next, an embodiment in which the method for taking out the solar cell substrate material according to the present invention is specifically applied will be described. In the following description, the first, second, and fourth steps are the same as described above, and the description is redundant. Therefore, the third step will be described in detail.

  First, in the first step, the terminal box 5 and the frame 6 of the used solar cell module 10 (see FIG. 1) were removed by a mechanical method to obtain a module 20 in the middle of dismantling of 20 mm square size.

  Next, in the second step, the module 20 in the middle of disassembly was immersed in an about 65 wt% nitric acid solution for about 6 hours to perform chemical treatment, thereby obtaining a module 30.

  Subsequently, in the third step, the module 30 in the middle of disassembly after the chemical treatment was sufficiently washed with pure water, and then charged into the reactor 80 and exposed to a supercritical atmosphere. In this example, the supercritical atmosphere was formed using water alone as a medium.

  In such a form, the reactor 80 having an inner diameter of 29.5 mm, a height of 75 mm, and an internal volume of about 51.2 ml was used. Moreover, the volume of the pipe part to the pressure gauge was about 17.7 ml (pipe inner diameter 3.2 mm, length 2.2 m), and the total volume was about 68.9 ml.

  The amount of water as a medium was 21.3 ml in this example. Here, an acid solution or alkaline solution of about 1% may be added to water. For example, acetic acid or sulfuric acid can be used as the acid solution, and sodium hydroxide or potassium hydroxide can be used as the alkaline solution. As a result, it is possible to expect the effect of reducing the decomposition of EVA or the adhesion between the EVA and the glass interface.

  In the reactor 80, the atmospheric temperature was set to about 374 ° C., and the atmospheric pressure was controlled to 23 MPa. And the atmosphere holding time was secured for 60 minutes under these conditions.

  As a result, the module 30 exposed to the atmosphere of the reaction furnace 80 is hydrolyzed by the back cover 3 made of PET (polyethylene terephthalate) or a fluorine-based material. Moreover, EVA2 which encloses the photovoltaic cell 1 is decomposed | disassembled into jelly form, and will be in the state which can be removed. Further, the interface between the front cover 4 and the EVA 2 is in a peelable state (see FIG. 5).

  In the third step, not only the atmosphere in the reaction furnace 80 is formed using water as a medium, but also methanol or ethanol may be used as a medium. Moreover, when forming the atmosphere of the reaction furnace 80 using a carbon dioxide as a medium, the quantity of the carbon dioxide which is a medium shall be 45 ml. Then, it is preferable to form a carbon dioxide critical atmosphere by controlling the atmospheric temperature of the reactor 80 to 120 ° C. and the atmospheric pressure to 20 MPa. Further, the atmosphere holding time is preferably secured for 60 minutes in order to promote the reaction with EVA.

  Furthermore, when the atmosphere of the reaction furnace 80 is formed using acetic acid as a medium, the amount of acetic acid as a medium is 25 ml. Then, it is preferable to form an acetic acid critical atmosphere by controlling the atmospheric temperature of the reaction furnace 80 to 321 ° C. and the atmospheric pressure to 5.8 MPa. In addition, the atmosphere holding time is preferably 30 minutes in order to promote the reaction with EVA.

  In the module 30, even in an atmosphere of these media, the back cover 3 is hydrolyzed and pulverized in the same manner as described above, and the EVA 2 enclosing the solar battery cell 1 is decomposed into a jelly shape, The interface between the front cover 4 and the EVA 2 becomes peelable.

  Next, as shown in FIG. 6, in the fourth step, the re-solidified EVA 2 is mechanically cut off at the interface of the solar cells 1 to take out the solar cells 1 and perform an appropriate acid treatment or alkali treatment. Thus, the silicon substrate material 11 was obtained.

  In the above embodiment, the case where the supercritical or subcritical atmosphere in the third step is formed by using water, carbon dioxide, methanol, ethanol, or acetic acid alone as a medium has been described. Without being limited thereto, water, carbon dioxide, methanol, ethanol, or a mixture of acetic acid may be used as the medium. For example, when a mixture of water and acetic acid is used as a medium, a mixture having a mixing ratio of about 20: 1 and a total amount of 21 ml is used, the atmospheric temperature is controlled to 373 ° C., the atmospheric pressure is controlled to 22 MPa, and the atmosphere is maintained. The time is preferably 60 minutes or more.

  The method for taking out the solar cell substrate material of the present invention is effective for use in business establishments in which the silicon substrate material is taken out from the crystalline silicon solar cell module that has been conventionally disposed of and recycled.

It is a schematic sectional drawing which shows an example of the solar cell module before taking out silicon substrate material. It is a schematic sectional drawing which shows the solar cell module in the middle of the disassembly by the taking-out method of the solar cell substrate material of this invention. It is a perspective view explaining 1 process of the taking-out method of the solar cell substrate material of this invention. It is the schematic which shows an example of the reaction furnace in the taking-out method of the solar cell substrate material of this invention. It is a schematic sectional drawing explaining 1 process of the taking-out method of the solar cell substrate material of this invention. It is a schematic sectional drawing which shows a mode that a photovoltaic cell is taken out by the taking-out method of the solar cell substrate material of this invention. It is a schematic sectional drawing of the photovoltaic cell taken out by the taking-out method of the solar cell substrate material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell 11 Silicon substrate material 12 Anti-reflective film 13 Silver electrode 14 Solder 10 Solar cell module 20, 30 Module in the middle of disassembly 2 EVA
3 Back cover 4 Front cover (light-receiving surface glass)
5 Terminal box 6 Frame 50 Container 60 Chemical solution 80 Reactor

Claims (10)

A method of taking out a substrate material in a solar battery cell from a solar battery module in which a solar battery cell surrounded by EVA and a light-receiving surface glass is laminated,
A method for removing a solar cell substrate material, comprising: exposing the solar cell module to a supercritical atmosphere or a subcritical atmosphere and decomposing the EVA to take out a substrate material in a solar cell.   The method for extracting a solar cell substrate material according to claim 1, wherein the supercritical atmosphere or subcritical atmosphere uses water, carbon dioxide, methanol, ethanol, or acetic acid as a medium.   The supercritical atmosphere or subcritical atmosphere using water as a medium has a temperature within a range of 374.2 ± 100 ° C and an atmospheric pressure within a range of 22.1 ± 10 MPa. 3. A method for taking out the solar cell substrate material according to 2. The method for taking out a solar cell substrate material according to claim 2 or 3, wherein an acid solution or an alkali solution is added when water is used as a medium in a supercritical atmosphere or a subcritical atmosphere.   The supercritical atmosphere or subcritical atmosphere using methanol as a medium has a temperature in a range of 239.9 ± 100 ° C. and an atmospheric pressure in a range of 8.1 ± 5 MPa. 3. A method for taking out the solar cell substrate material according to 2.   The supercritical atmosphere or subcritical atmosphere using ethanol as a medium has a temperature within a range of 242.2 ± 100 ° C and an atmospheric pressure within a range of 6.36 ± 5 MPa. 3. A method for taking out the solar cell substrate material according to 2.   The supercritical atmosphere or subcritical atmosphere using carbon dioxide as a medium has a temperature in the range of −10 ° C. to + 100 ° C. with respect to the supercritical temperature of 31.1 ° C., and the atmospheric pressure in the range of 7.39 ± 5 MPa. The method for taking out the solar cell substrate material according to claim 2, wherein   The supercritical atmosphere or subcritical atmosphere using acetic acid as a medium has a temperature in a range of 321.4 ± 100 ° C and an atmospheric pressure in a range of 5.79 ± 3 MPa. 3. A method for taking out the solar cell substrate material according to 2.   The time until the atmosphere reaches a predetermined temperature is 5 minutes or more, and the time until the temperature is lowered to room temperature after being held at the temperature is 5 minutes or more. The method for taking out the solar cell substrate material described in 1. Before putting a solar cell module into a supercritical atmosphere or a subcritical atmosphere, chemical | medical solution immersion processes, such as nitric acid, sodium hydroxide, and a trichloroethylene, are given, The any one of Claims 1-9 characterized by the above-mentioned. A method for taking out the solar cell substrate material.

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