JP2002009320A - Method for manufacturing solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a solar battery from such waste as silicon powder that is generated when machining a silicon single crystal or polycrystal. SOLUTION: Powder with silicon as a main constituent is taken out of waste slurry that is generated when cutting the ingot of a silicon crystal, and is compressed into a plate. First, the plate is dipped into a fluoric acid solution and then into pure water to remove an oxygen atom from silicon oxide for covering the surface of the silicon particle for composing the plate before drying. Moisture in the plate is evaporated by drying, and silicon particles that have approached are connected via a gap to form a porous body. Then, after the plate is crimped to the conductive layer of the substrate, PN junction is formed at silicon for forming the porous body. By providing a metal electrode while sandwiching the PN junction with the conductive layers, the solar battery is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a powder containing silicon as a main component from waste generated when processing an ingot made of, for example, a single crystal or polycrystal of silicon, and converting a solar cell from the powder. On how to make.

[0002]

2. Description of the Related Art In general, a solar cell is obtained by cutting a wafer obtained by cutting (slicing) a silicon single crystal or silicon polycrystal ingot with a wire saw, for example.
It is manufactured by forming a junction and providing electrodes on the front and back of the wafer so as to sandwich the PN junction. For cutting the wafer, for example, an apparatus called a wire saw is used. This apparatus comprises, for example, a wire group formed by winding a single wire between a plurality of rollers at a predetermined pitch, and pressing the ingot against the wire while rotating the wire at a high speed by rotating the rollers, and also forming a slurry containing abrasive grains into the ingot. And a plurality of wafers are simultaneously obtained by supplying to a contact portion between the wafer and the wire.

[0003]

Although solar cells are effective in saving energy, the biggest drawback is that the cost is high because the silicon crystal as a raw material is expensive. In addition, the shortage of raw material silicon has been spurred by the increase in the production of solar cells.

On the other hand, in a wire saw, a slurry containing abrasive grains is circulated. However, if the amount of silicon chips in the slurry increases, the cutting function deteriorates. Therefore, after circulating a predetermined number of times, the slurry is discarded as waste slurry. In other words, at present, the waste slurry contains wasteful and scarce precious silicon, but is wasted.

The present invention has been made in view of such circumstances, and an object of the present invention is to manufacture a solar cell at low cost by using silicon-containing waste generated by processing of silicon crystal such as cutting and polishing. It is to provide a method.

[0006]

SUMMARY OF THE INVENTION A method of manufacturing a solar cell according to the present invention recovers a powder mainly composed of silicon from waste generated when processing or crushing P-type (N-type) silicon. A collecting step, a step of removing silicon oxide from the collected powder, a step of attaching a layer of the collected powder to a surface of a conductor forming one electrode before or after this step, Forming a PN junction by forming an N-type (P-type) silicon layer on the surface of the powder layer from which the P-type silicon has been removed; and forming another electrode on the N-type (P-type) silicon layer. And a step of providing

According to such a method, silicon oxide is removed from a powder containing silicon as a main component, which has been conventionally discarded, so that a material for a solar cell which can be substituted for a silicon wafer can be produced. Effective utilization can be achieved.

[0008] Before or after the above-mentioned step of removing silicon oxide, a step of compressing the recovered powder to form a plate, and applying the plate obtained in this step to one electrode. The step of attaching the plate to one of the electrodes may be performed by, for example, crimping.

In these methods, the step of removing silicon oxide from the recovered powder or the plate formed from the powder is, for example, reacted with hydrofluoric acid, then reacted with water, and then dried. Can be by way,
Further, the electrode may include a transparent electrode.

Further, the waste used as a raw material in the present invention includes, for example, swarf when a silicon ingot is cut by a wire saw, wafer polishing debris, and wafer crushed debris.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for manufacturing a solar cell according to the present invention will be described below, taking as an example a case where powder obtained from waste slurry discharged from a wire saw is used as a raw material. The present embodiment proceeds by the steps shown in FIG.
First, a description will be given of an example of a case where a wire saw shown in FIG. 2 is used in a recovery step 1 until a powder containing silicon (Si) as a main component is recovered.

The wire saw is formed by winding one wire serving as a cutting means at a predetermined pitch between, for example, three processing rollers 11 and stretching the wire. A slurry obtained by dispersing abrasive grains made of (SiC) in a water-soluble or oil-based dispersant is circulated and supplied from a slurry tank 13 through a supply pipe 14 and a slurry supply means 15, and is supplied above the wire group 11. By lowering an ingot 16 of N-type or P-type monocrystalline silicon or polycrystalline silicon, which is an object to be cut, from the side so as to pass through the wire group 12, the ingot 16 is cut (sliced), and a large number of wafers are cut. Are simultaneously obtained. Here, the water-soluble dispersant includes, for example, those based on water to which glycols, surfactants, higher fatty acids and the like are added, and the oil-based dispersants include, for example, lubricants for oils such as mineral oils. And the like can be mentioned.

In this cutting process, the slurry supply means 1
The slurry supplied from 5 to the wire group 11 is stored in the slurry tank 13 via the receiving tank 17, but when the ingot 16 is sliced, chips of the ingot 16 and crushed abrasive grains are mixed in the slurry, and these are often mixed. Since the slicing accuracy is deteriorated, a part of the slurry is appropriately discharged as waste slurry to the waste slurry tank 19 via the discharge pipe 18 and the supply port 1
New slurry is supplied to the slurry tank 13 via 3a.

Since the waste slurry produced here contains, for example, about 50% by weight of a dispersant as a main component, the separation step 19a
To remove the dispersant. As an example of the separation step 19a, first, filtration is performed by, for example, a centrifuge to separate most of the dispersant and clay-like solid, and the solid is washed with an organic solvent, preferably acetone. The remaining dispersant attached to the solid content is removed, and a powder containing silicon as a main component (silicon powder) is obtained through processes such as filtration and drying.

In the present embodiment, in addition to the powder obtained as a raw material as described above, the powder used as a raw material may be a wafer, a grinding process during an IC manufacturing process, for example, a single-side grinding such as a back grinder or SOI wafer manufacturing process. Use silicon powder recovered from waste generated during double-head grinding during wafer preparation, or silicon powder generated when polishing a silicon wafer or crushing offcuts (a wafer corresponding to the end of an ingot). You can also. In these powders, for example, in the powder collected by the above-mentioned wire saw, in addition to silicon chips, for example, a small amount of metal powder or the like, which is a crushed abrasive or a worn piece of a wire, can be mixed. When diamond is used as a processing means of silicon crystal, for example, cutting means, diamond dust may be mixed in, but these contaminants have little effect on the production of solar cells, so they are usually not separated and used as raw materials. Use and separate as necessary.

Returning to the process diagram of FIG. 1, the silicon powder recovered in the recovery step 1 as described above is then sent to a compression step 2 where the silicon powder is pressed into, for example, a plate by a press molding machine. Is done. Although the powder (grain) is tightly adhered to the plate so as to be integrated as a solid as a whole, the inside of the plate is such that an acid solution can enter in an acid immersion step 31 described later as shown in FIG. Is compressed so as to leave a gap 21. The gap 21 is a space necessary for removing a thin silicon oxide (SiO 2) layer (surface layer 23) formed on the surface of each silicon (Si) particle 22 constituting the powder. Is formed by exposing the surface of the silicon crystal to high temperature due to friction when the silicon crystal is subjected to the above-described processing or crushing.

Next, the silicon oxide removing step 3 for removing silicon oxide formed on the silicon powder constituting the plate will be described.
It comprises an acid immersion step 31, a pure water immersion step 32, and a drying step 4. The acid immersion step 31 is to immerse the plate in, for example, a concentrated hydrofluoric acid (50%) solution in order to cut off the bond between silicon and oxygen constituting silicon oxide in the plate. When the plate is immersed, H
The F solution enters the plate through the gap 21 and separates oxygen atoms bonded to silicon atoms by the reaction shown in the equation (1), and hydrogen (H) atoms or fluorine (F) ) The atoms bond. SiO2 + 4HF → SiF4 + 2H2O (1) FIGS. 4 and 5 are diagrams schematically showing the state of the surface layer 23 of the silicon powder 22 before and after the reaction with the HF solution, respectively.

Immersion in an HF solution (acid immersion step 3)
The plate after 1) is immersed in pure water (pure water immersion step 32). When the plate is immersed in pure water, the oxygen atoms are cut off and the fluorine atoms bonded to the silicon atoms are replaced by hydroxyl groups as shown in FIG. At this time, the site where the hydrogen atom is bonded to the silicon atom remains unchanged.

In this manner, a plurality of rows of silicon atoms having the same structure are formed in the surface layer 23. The hydroxyl groups substituted with fluorine atoms are, for example, as shown by A1 in FIG. The hydrogen atoms remaining without being replaced in other rows are attracted to each other, and as a result, the rows of atoms formed in a chain approach each other. By drying the plate in such a state (drying step 4), the hydrogen atoms and oxygen atoms approaching each other become water vapor (H 2 O), evaporate, and are separated from the silicon atoms. In the acid immersion step 31, a part of the Si—O bond slightly substituted without being replaced by a fluorine atom is diffused outward by the drying step 4.

When the drying step 4 is completed, since the rows of silicon atoms are close to each other as described above, each silicon atom (or row of silicon atoms) has a hydrogen atom bonded thereto as shown in FIG. The removal of the atoms and the hydroxyl groups results in the bonding, and as a result, silicon oxide, which is an insulator, is removed from the surface layer 23.

The transport of the plate in the silicon oxide removing step 3 is preferably performed in an inert gas atmosphere such as nitrogen or argon or a reduced pressure atmosphere. The reason is that in order for the silicon particles to combine and allow electricity to flow, it is necessary that silicon oxide does not intervene at the particle interface between the silicon particles.

FIG. 9 is a schematic plan view showing an example of such a processing apparatus, and the processing apparatus will be described with reference to FIG. The silicon powder plated in the compression step 2 is set in the cassette C and is carried into the load lock chamber 61,
It is placed on the loading tray 62. Thereafter, the gate valves V1 and V2 on the atmosphere side and the processing chamber side are closed, and nitrogen (N
2) After setting the gas atmosphere, the gate valve V2 is opened, and the cassette C is moved by the divided transport belt (not shown).
Is carried into the processing chamber 62. The inside of the processing chamber 63 is set to a nitrogen gas atmosphere, and the cassette C is transferred to the chemical solution tank 65, the washing tank 66, and the drying unit 67 in this order by the gripping arm 64 movable in the X direction. 3
1. Each step of the pure water immersion step 32 and the drying step 4 is performed.
Then, the cassette C is carried out of the load lock chamber 61 via a route reverse to the above-described route.

Next, a process of manufacturing a solar cell from a plate from which silicon oxide has been removed will be described. First, the plate and the substrate forming one electrode are joined (one electrode forming step 5). In the one electrode forming step 5, the two are pressed together by pressing the plate in close contact with the substrate, and the pressure is set to be higher than, for example, the compression step 2 in which the powder is formed into a plate. As a result, the plate 7 has a shape (a porous silicon body 71) in which a gap a slightly remains between the compressed silicon powders as shown in FIG.
2 attached. As described above, since at least the surface of the substrate 72 serving as one electrode needs to have conductivity, a resin film such as a plastic film obtained by depositing a metal such as aluminum or stainless steel on the surface is used. The conductive layer 73, which is a conductor formed by the above, is electrically connected to the porous silicon body (plate) 71.

Then, a PN junction is formed in the porous silicon body 71 (PN junction step 51). The PN junction can be formed by, for example, assuming that the silicon porous body 71 is P-type, by forming an N-type layer on the upper surface side by diffusion of N-type impurities such as phosphorus (P), or CV on top
A method of depositing an N-type semiconductor thin film by D or the like can also be adopted.

In this manner, the porous silicon body 71 is formed, for example, as shown in FIG.
1 is formed, and an I-type junction is formed on the upper surface of the N-type layer.
A TO (transparent electrode) 74 is formed on the entire surface, and a metal electrode 75 made of, for example, aluminum or stainless steel is provided thereon, for example, in a comb shape (the other electrode forming step 52), thereby completing the solar cell. In this example, ITO 74 and metal electrode 7
5 constitutes the other electrode. Since, for example, a comb-shaped electrode as shown in FIG. 12 is used as the metal electrode 75, for example, sunlight is formed at a PN junction through an exposed portion of the silicon porous body 71 above the metal electrode 75 without the metal electrode 75. Incident on the part, and generates an electromotive force. 11 and 12, the porous silicon body 71 is shown in the form of a plate for convenience of drawing, and the gap a is omitted.
The plate portion (P-type layer and N-type layer) formed by 1 is drawn thicker than it actually is.

As described above, according to the present embodiment, for example, waste slurry generated when a wafer for a solar cell is cut out from silicon single crystal or silicon polycrystal, or crushed debris generated when crushing offcuts of a silicon wafer , A powder containing silicon as a main component is recovered, and the powder is formed into a plate, for example, and silicon oxide formed on the silicon surface is removed. It is possible to create a solar cell material which can be used instead of the above, and it is possible to effectively use resources.

In the above-mentioned plate, when removing silicon oxide from the recovered powder, each step of immersion in an acid solution and immersion in pure water is performed to separate oxygen atoms bonded to silicon atoms and to separate silicon atoms from each other. Because the particles that form the silicon powder are bonded together, silicon forms a porous body, and by converting the silicon plate that forms the porous body into a solar cell, a solar cell with high light absorption can be made. it can.

Furthermore, when silicon-containing waste is used for a solar cell, there is little effect even if silicon carbide (SiC) and diamond are mixed in the waste, so that there is an advantage that separation cost is not required. There is, for example, a case where abrasive grains using silicon carbide are used for processing of a silicon crystal such as cutting, and a silicon-containing waste generated when a diamond blade is used.

The acid immersion step 3 in the present embodiment
The acid solution used in 1 is not limited to hydrofluoric acid, but may be an alkali such as KOH. In addition, the silicon after removing the silicon oxide and the substrate 7 provided with the conductive layer 73 on the surface.
2 (one electrode forming step 5 in FIG. 1)
The present invention is not limited to the pressure bonding described in the above embodiment. For example, the silicon powder from which silicon oxide has been removed may be mixed with a dispersant to form a slurry, and the slurry may be applied to the conductive layer 73 and then the dispersant may be evaporated. Good.

Further, the above-described substrate 72 may be a metal plate or a resin substrate with a metal film attached thereto. Further, the “plate” in the present invention includes so-called pellets and the like.

The recovery step 1 in the above embodiment
The method for forming a solar cell from the powder (silicon powder) obtained by the method described above is as follows.
The method is not limited to the method of forming. For example, an adhesive layer made of, for example, a polymer adhesive is formed on the surface of the conductive layer 73 on the surface of the substrate 72, a single layer of P-type silicon powder is deposited on the adhesive layer, and an N-type silicon thin film is sequentially formed thereon. And an ITO film forming an electrode may be deposited. In such a method, the silicon powder is preferably a single crystal, and when the silicon powder is N-type, a thin film of P-type silicon may be deposited.

[0032]

As described above, according to the present invention, a solar cell is manufactured at a lower cost than the conventional one by using silicon-containing waste generated by processing of silicon crystal such as cutting and polishing and crushing of scraps. be able to.

[Brief description of the drawings]

FIG. 1 is a process chart showing a manufacturing process of a solar cell according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a recovery process from recovery of silicon powder as a raw material of a solar cell from waste slurry of a wire saw.

FIG. 3 is an enlarged cross-sectional view illustrating a state of the powder collected in the recovery step and formed into a plate in the compression step and silicon particles constituting the powder.

FIG. 4 is a schematic diagram illustrating a structure inside a surface layer of the silicon particles.

FIG. 5 is a schematic diagram illustrating a structure inside the surface layer of the silicon particles and a change thereof.

FIG. 6 is a schematic diagram for explaining a structure inside the surface layer of the silicon particles and a change thereof.

FIG. 7 is a schematic diagram illustrating a structure inside the surface layer of the silicon particles and changes thereof.

FIG. 8 is a schematic diagram for explaining a structure inside the surface layer of the silicon particles and a change thereof.

FIG. 9 is a schematic plan view illustrating a plate processing apparatus.

FIG. 10 is a cross-sectional view showing a state of bonding between a silicon porous body and a substrate (conductive layer) in one electrode forming step.

FIG. 11 is a schematic sectional view showing an example of a solar cell manufactured according to the present embodiment.

FIG. 12 is a schematic perspective view showing an example of a solar cell manufactured according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recovery process 2 Compression process 23 Surface layer 3 Silicon oxide removal process 31 Acid immersion process 32 Pure water immersion process 4 Drying process 5 One electrode formation process 51 PN junction formation process 52 The other electrode formation process 72 Substrate 73 Conductive layer 75 Metal electrode

Claims (6)

[Claims] 1. A recovery step for recovering a powder mainly composed of silicon from waste generated when processing or crushing P-type (N-type) silicon, and removing silicon oxide from the recovered powder. A step of, before or after this step, attaching a layer of the recovered powder to the surface of the conductor forming one electrode; and forming an N-type on the surface of the layer of the powder from which silicon oxide has been removed. Forming a (P-type) silicon layer to form a PN junction; and providing another electrode on the N-type (P-type) silicon layer. Production method. 2. A recovery step of recovering a powder containing silicon as a main component from waste generated when processing or crushing P-type (N-type) silicon; A step of removing the silicon oxide from the plate, a step of compressing the recovered powder before or after this step to form a plate, and a step of combining the plate obtained in this step with one side. Attaching a N-type (P-type) silicon layer to the surface of the plate to form a PN junction; Providing a second electrode on the (P-type) silicon layer. 3. The method for manufacturing a solar cell according to claim 2, wherein the step of attaching the plate to the surface of the conductor is a step of pressing the plate to the surface of the conductor. 4. The step of removing silicon oxide from the recovered powder or a plate formed from the powder is a step of reacting with hydrofluoric acid, then reacting with water, and then drying. The method for manufacturing a solar cell according to claim 1, 2 or 3, wherein: 5. The method for manufacturing a solar cell according to claim 1, wherein the other electrode includes a transparent electrode. 6. The waste according to claim 1, wherein the waste is at least one of cutting chips, wafer polishing debris and wafer crushed debris when the silicon ingot is cut by a wire saw. A method for manufacturing the solar cell according to the above.