JP2016098142A - Production method of polycrystalline silicon ingot, production method of usage of polycrystalline silicon ingot, and polycrystalline silicon ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a polycrystalline silicon ingot capable of producing, with excellent controllability, a polycrystalline silicon ingot with low crystal defect density and of high quality preferable as an ingot for a solar cell, so as to provide a polycrystalline silicon ingot at a low cost with high quality, and a usage thereof.SOLUTION: A polycrystalline silicon lump 1 whose average crystal grain size is 15 mm or less is arranged on an upper face of a base plate of a crucible 3. Then a silicon raw material 2 is put in the crucible, and the silicon raw material put therein is fused and unidirectionally solidified to manufacture a polycrystalline silicon ingot.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a polycrystalline silicon ingot, a method for manufacturing a polycrystalline silicon ingot, and a polycrystalline silicon ingot.

  The use of natural energy is attracting attention as an alternative to oil, which is causing various problems in the global environment. Among them, the solar cell does not require a large facility and does not generate noise during operation, and thus has been particularly actively introduced in Japan and Europe.

  Solar cells using compound semiconductors such as cadmium tellurium have also been put into practical use, but solar cells using crystalline silicon substrates are large in terms of the safety of the materials themselves, past achievements, and cost performance. Solar cells using a polycrystalline silicon substrate (polycrystalline silicon solar cells) occupy a large share.

  A polycrystalline silicon wafer, which is generally widely used as a substrate for polycrystalline silicon solar cells, is an ingot produced by a method called a casting method in which a molten silicon is unidirectionally solidified in a crucible to obtain a large polycrystalline silicon ingot. It is cut into blocks and made into wafers by slicing.

  The polycrystalline silicon wafer manufactured by the casting method generally has a distribution in the output characteristics of the solar cell as shown in FIG. 8 depending on the position in the height direction in the ingot or block.

  The reason why the characteristic distribution of FIG. 8 occurs is generally explained as follows. First, in the region I at the initial stage of unidirectional solidification, the characteristics deteriorate due to the influence of impurities diffused from the crucible. In the region II on the upper side, since the incorporation of impurities in the raw material due to segregation and the occurrence of crystal defects are few, the characteristics are the best in the block. Further, in the upper region III, the amount of impurities taken into the crystal gradually increases, crystal defects increase, and the characteristics deteriorate compared to the region II. Further, in the region IV on the upper side, in the same manner as in the region III, in addition to further increasing the amount of impurities incorporated into the crystal and crystal defects, impurities formed on the uppermost surface portion after the ingot solidifies to the end. Impurity reverse diffusion occurs from the high-concentration portion, and the amount of impurities further increases, so that the characteristic deterioration becomes more remarkable than in the region III.

  In the above description, the influence of impurities in the raw material and impurities eluted from the crucible is considered, but even if there is no such influence, in regions III and IV, crystals that become minority carrier traps toward the top Since defects increase gradually, the characteristics of solar cells tend to deteriorate.

  Conventionally, a method for increasing the crystal grain size and bringing it closer to a single crystal has been proposed for improving the quality of a polycrystalline silicon ingot. However, recently, as described in Patent Document 1, for example, the crystal grain size is reversed. However, it has become clear that the smaller is the preferable ingot for a solar cell as a whole because the growth of crystal defects can be suppressed.

  The present inventor has so far proposed a method of growing a polycrystalline silicon ingot having a small crystal grain size by promoting the initial nucleation of silicon by setting the temperature change rate at the start of the growth of the polycrystalline silicon ingot to be small. (Patent Document 1).

  The present inventor has also proposed a method for arranging grains so as to promote generation of silicon crystal nuclei on the upper surface of the bottom plate portion of a casting mold for polycrystalline silicon ingot (Patent Document 2).

  In Patent Documents 3 and 4, a nucleation promotion layer is placed on the bottom of a casting mold for polycrystalline silicon ingot, a silicon raw material is loaded on the nucleation promotion layer, and at least one thermal parameter is controlled. A method has been proposed. The nucleation promoting layer is composed of a plurality of crystal particles having a random geometry, a size of less than 50 mm, and a material having a melting point higher than 1400 ° C., and the roughness of the interface with the silicon melt is 300 μm to 1000 μm. A micron plate has been proposed as a specific example.

JP2013-129580A JP 2013-177274 A US Patent Application Publication No. 2013-0136918 US Patent Application Publication No. 2014-0127496

  Even with the methods described in Patent Documents 1 and 2, good results have been obtained so far, but a method for producing a polycrystalline silicon ingot that is easy to control during production is desired.

  In addition, as an example of the nucleation promoting layer described in Patent Documents 3 and 4, in the case where the particles have a random geometry and are a plurality of crystal particles having a size of less than 50 mm, nucleation is partially promoted, resulting in high quality. Although polycrystalline silicon grows, there is a problem that it is not uniform in a plane and reproducibility cannot be secured.

  In addition, when fine crystal particles with a diameter of several millimeters are used as the nucleation promoting layer, the silicon crystal has a lower specific gravity than the silicon melt, so that it easily floats on the liquid surface and plays a role as a nucleation promoting layer. In this case, there seems to be a problem with reproducibility.

  As an example of the nucleation promoting layer described in Patent Documents 3 and 4, when a plate having a melting point higher than 1400 ° C. and a roughness of the interface with the silicon melt of 300 to 1000 microns is used, the plate and the silicon fusion layer are used. Nucleation is not always promoted depending on the wettability with the liquid and the period of characteristic change (such as wavelength) at the interface between the plate and the silicon melt. This method is also reproducible. There's a problem. Also, in the case where the plate used as the nucleation promoting layer is a material such as silicon that partially melts, the roughness of the interface between the plate and the silicon melt cannot be measured. There is also a problem that it cannot be controlled.

  In view of the above problems, the present invention provides a polycrystalline silicon ingot manufacturing method capable of manufacturing a high-quality polycrystalline silicon ingot having a low crystal defect density and preferable as an ingot for a solar cell with good controllability. An object is to provide a high-quality polycrystalline silicon ingot and its use.

  As a result of earnest research, the inventor of the present invention, when manufacturing a polycrystalline silicon ingot by unidirectionally solidifying the molten silicon in the crucible from the bottom to the top of the crucible, on the upper surface of the bottom plate portion of the casting mold for polycrystalline silicon ingot. The present inventors have found that the above problems can be solved by arranging a silicon lump having specific characteristics and growing polycrystalline silicon from the silicon lump.

  Thus, according to the present invention, a polycrystalline silicon lump having an average crystal grain size of 15 mm or less is disposed on the upper surface of the crucible bottom plate, and then the silicon raw material is charged into the crucible, and the injected silicon raw material is melted in one direction. There is provided a method for producing a crystalline silicon ingot which is solidified to obtain a polycrystalline silicon ingot.

  According to the present invention, there is provided a polycrystalline silicon ingot obtained using the polycrystalline silicon ingot produced by the polycrystalline silicon ingot producing method, wherein the polycrystalline silicon ingot is used for obtaining a use selected from a polycrystalline silicon block, a polycrystalline silicon wafer, and a solar cell. An application manufacturing method is provided.

  In addition, according to the present invention, there is provided a polycrystalline silicon ingot that is unidirectionally solidified and includes a boundary portion including a plurality of portions where the grain boundaries are discontinuous in the direction of unidirectional solidification. Is done.

  In the present specification, the “average crystal grain size of the polycrystalline silicon lump” does not mean the appearance size of the polycrystalline silicon lump, but is a direction perpendicular to the crucible bottom plate when arranged on the crucible bottom plate ( It means an average value of crystallographic sizes of one or a plurality of crystal regions existing in a polycrystalline silicon block as viewed from the upper side.

  The method for measuring the average crystal grain size of the polycrystalline silicon lump can be obtained, for example, by observing the whole polycrystalline silicon lump to be obtained, counting the number of crystal grains, and determining the area occupied by them. More simply, an approximate average crystal grain size is obtained by drawing a line segment of an appropriate length on a photograph of the polycrystalline silicon lump and counting the number of crystal grain boundaries included in the line segment. It is also possible.

  Further, in the present specification, the “solar battery” means a “solar battery cell” that constitutes a minimum unit and a “solar battery module” in which a plurality of them are electrically connected.

  According to the present invention, it is possible to produce a high-quality polycrystalline silicon ingot having a low crystal defect density and preferable as a solar cell ingot with good controllability. Further, by processing and processing the polycrystalline silicon ingot, it becomes possible to supply high-quality polycrystalline silicon blocks, polycrystalline silicon wafers, and polycrystalline silicon solar cells to the market at a low price.

It is sectional drawing which shows the schematic structure for demonstrating the basic process of the polycrystalline silicon ingot manufacturing method of embodiment. It is sectional drawing which shows the schematic structure for demonstrating the basic process of the polycrystalline silicon ingot manufacturing method of embodiment. It is sectional drawing which shows the schematic structure for demonstrating the basic process of the polycrystalline silicon ingot manufacturing method of embodiment. It is sectional drawing which shows the schematic structure for demonstrating the basic process of the polycrystalline silicon ingot manufacturing method of embodiment. It is principal part sectional drawing which shows schematic structure of the polycrystalline silicon ingot of embodiment. It is a schematic sectional drawing which shows an example of the apparatus used for the manufacturing method of the polycrystalline silicon ingot of embodiment. It is a graph which shows the relationship between the average crystal grain diameter of the polycrystalline silicon lump in Examples 1-10 and a comparative example, and the incidence rate of the photovoltaic cell output ranks 1-3. It is a conceptual diagram which shows the relationship between the position of the height direction of a common polycrystalline silicon ingot, and the output of the produced solar cell.

  Hereinafter, a polycrystalline silicon ingot manufacturing method, a polycrystalline silicon block, a polycrystalline silicon wafer, a solar cell manufacturing method, and a polycrystalline silicon ingot according to embodiments of the present invention will be described with reference to the drawings.

  1 to 4 are sectional views showing a schematic structure for explaining the method for manufacturing a polycrystalline silicon ingot according to the present embodiment. 1-4, 1 is a polycrystalline silicon lump, 2 is a silicon raw material, 3 is a crucible, and 4 is polycrystalline silicon solidified in one direction.

  In the polycrystalline silicon ingot manufacturing method of the present embodiment, a polycrystalline silicon lump 1 having an average crystal grain size of 15 mm or less is arranged on the upper surface of the bottom plate of the crucible 3, and then the silicon raw material 2 is put into the crucible 3. A silicon raw material is melted and then solidified in one direction to obtain a polycrystalline silicon ingot.

  A series of basic steps will be described. First, as shown in FIG. 1, a polycrystalline silicon lump 1 having an average crystal grain size of 15 mm or less is arranged on the upper surface of the bottom plate of the crucible 3, and silicon is put in the crucible 3. Raw material 2 is charged.

  Next, as shown in FIG. 2, the silicon raw material 2 put in the crucible 3 is heated so as to melt. Here, the polycrystalline silicon lump 1 is not completely melted and at least a part of the polycrystalline silicon lump 1 is left.

  Subsequently, as shown in FIG. 3, the melted silicon raw material 2 is cooled upward from the bottom plate side of the crucible 3 to solidify the polycrystalline silicon 4 in the direction of the arrow in FIG. The crucible 3 is solidified in one direction from the bottom plate side. Here, since there is a high tendency to perform epitaxial growth inheriting the orientation of the crystal grains from the crystal grains of the undissolved polycrystalline silicon lump 1, the average crystal grain size of the polycrystalline silicon 4 that is initially grown is determined by the bottom plate of the crucible 3. There is a tendency to be almost equal to the average crystal grain size of the polycrystalline silicon lump 1 disposed on the upper surface. Therefore, by using the polycrystalline silicon lump 1 having an average crystal grain size of 15 mm or less, it is possible to grow polycrystalline silicon 4 having substantially the same crystal grain size.

  Thereafter, as shown in FIG. 4, cooling is performed until the upper surface of the molten silicon raw material 2 is solidified.

  As described above, by using the polycrystalline silicon lump 1 having an average crystal grain size of 15 mm or less, it is possible to grow polycrystalline silicon 4 having substantially the same crystal grain size, the crystal defect density is low, and the solar cell. It is possible to manufacture a high-quality polycrystalline silicon ingot preferable as an ingot for use with good controllability.

  In the polycrystalline silicon ingot produced by the polycrystalline silicon ingot producing method of the present embodiment, epitaxial growth occurs in all the crystal grains of the polycrystalline silicon lump 1, as shown in FIG. Therefore, when the cross section of the interface portion between the polycrystalline silicon lump 1 and the unidirectionally solidified polycrystalline silicon 4 is observed, portions A, B, and C where the crystal grains are discontinuous are seen. The point is a feature of the polycrystalline silicon ingot of the present embodiment. FIG. 5 shows a portion including a boundary portion including a plurality of portions where the crystal grain boundaries are discontinuous in the direction solidified in one direction.

  As the polycrystalline silicon lump 1, a part or all of the polycrystalline silicon ingot can be used. For example, it may be a part of a polycrystalline silicon ingot for a solar cell cut from a polycrystalline silicon ingot having a height of 200 mm or more manufactured using a casting method, or a height of 10 mm similarly manufactured using a casting method. A part or all of the polycrystalline silicon ingot of the order may be used.

  In addition, for example, a polycrystalline silicon ingot grown by bringing a silicon growth substrate into contact with a silicon melt, a polycrystalline silicon ingot that is solidified by pouring a silicon melt into a material having a melting point of silicon or lower, and silicon It is also possible to use a polycrystalline silicon ingot or the like obtained by partially or entirely melting and solidifying these grains by energy irradiation such as a heater or a laser.

  Among them, the bottom is more preferable as the polycrystalline silicon lump 1 when using a part of polycrystalline silicon obtained by a casting method (unidirectional solidification of silicon melt). Here, the bottom portion is a portion cut out from within one third of the height direction from the bottom surface of the polycrystalline silicon ingot.

  Among the bottom parts, a polycrystalline silicon lump cut out in a direction parallel to the bottom (bottom) surface is more suitable from the viewpoint of crystal grain size, and it is most preferable to use a bottom side end material that is not used for solar cells. preferable. The reason is that the bottom end material is not only a part that is not used for solar cells, but is also suitable from the viewpoint of crystal grain size and has few crystal defects such as dislocations. This is because it is optimal for becoming the growth starting point of the crystalline silicon ingot.

The polycrystalline silicon ingot manufacturing apparatus that can be used in the polycrystalline silicon ingot manufacturing method of the present embodiment is not particularly limited, and can be implemented using a known manufacturing apparatus. However, the side heater type and the top heater type are more suitable because the temperature distribution in the crucible vertical direction is easily provided. Even side heaters can be used by considering the balance between heat removal from the crucible bottom and heat input from the heater.
(Production method of polycrystalline silicon ingot)
Although the manufacturing method of the polycrystalline silicon ingot of this Embodiment is demonstrated more concretely based on drawing below, this invention is not limited to this Embodiment.

  The method for manufacturing a polycrystalline silicon ingot of the present embodiment can also be implemented using a known apparatus as shown in FIG.

  FIG. 6 is a schematic cross-sectional view showing an example of an apparatus used in the method for manufacturing a polycrystalline silicon ingot of the present embodiment.

  This apparatus is generally used for producing a polycrystalline silicon ingot, and has a chamber (closed container) 9 constituting a resistance heating furnace.

  A crucible 3 made of graphite, quartz (SiO 2) or the like is disposed inside the chamber 9 so that the atmosphere inside the chamber 9 can be maintained in a sealed state.

  In the chamber 9 in which the crucible 3 is accommodated, a graphite crucible base 6 that supports the crucible 3 is arranged. The crucible base 6 can be moved up and down by a lift drive mechanism 14, and the refrigerant (cooling water) in the cooling tank 13 is circulated therein.

  An outer crucible 5 made of graphite or the like is disposed on the upper part of the crucible base 6, and the crucible 3 is disposed therein. Instead of the outer crucible 5, a cover made of graphite or the like surrounding the crucible 3 may be disposed.

  A resistance heating body 12 such as a graphite heater is disposed so as to surround the outer crucible 5, and a heat insulating material 10 is disposed so as to cover these from above.

  The resistance heating body 12 can be heated from the periphery of the crucible 3 to melt the silicon raw material 2 in the crucible 3.

  Heating by the resistance heater 12, cooling from the lower side of the crucible 3 by the cooling tank 13, and raising and lowering of the crucible 3 by the elevating drive mechanism 14 can provide a temperature distribution in the vertical direction in the crucible, and on the crucible bottom plate The form and arrangement of the heating mechanism such as a heating element are not particularly limited as long as the silicon raw material can be melted while leaving a part or all of the arranged polycrystalline silicon lump.

  In order to detect the temperature of the bottom surface of the crucible 3, a crucible lower thermocouple 7 is disposed in the vicinity of the center of the lower surface of the crucible 3, and an outer crucible thermocouple 8 is disposed in the vicinity of the center of the outer surface of the outer crucible 5, and these outputs are controlled 11, and the heating state by the resistance heating body 12 is controlled. In addition to the thermocouple described above, a thermocouple or a radiation thermometer for detecting temperature may be arranged.

  The inside of the chamber 9 can be kept in a sealed state so that external oxygen gas, nitrogen gas, etc. do not flow in. Normally, after the silicon raw material such as polycrystalline silicon is charged and before the melting, A vacuum is applied, and then an inert gas such as argon gas is introduced to maintain an inert atmosphere.

  With the apparatus having such a configuration, basically, the silicon raw material 2 is filled into the crucible 3, degassing (evacuation), gas replacement in the chamber 9 by introducing an inert gas, melting of the silicon raw material 2 by heating, A polycrystalline silicon ingot is manufactured through the steps of melting confirmation and holding, temperature control and solidification start by operation of the elevation drive mechanism 14, solidification completion confirmation and annealing, and ingot removal.

1 to 4 are simplified sectional views showing the inside of the crucible 3 in the polycrystalline silicon ingot manufacturing method of the present embodiment. First, as shown in FIG. 1, a polycrystalline silicon lump 1 having an average crystal grain size of 15 mm or less is arranged on the bottom plate of the crucible 3, and a silicon raw material 2 is filled thereon. After deaeration (evacuation) and replacement of inert gas in the apparatus, the upper part of the crucible 3 is controlled to be heated and removed so that the temperature is higher than the lower part, leaving part or all of the polycrystalline silicon lump. The silicon raw material is melted (FIG. 2). Thereafter, unidirectional solidification is performed from below (FIG. 3), and the whole is solidified (FIG. 4). Thereafter, annealing can be performed to obtain a high-quality polycrystalline silicon ingot with good controllability. The polycrystalline silicon lump 1 disposed on the bottom plate of the crucible 3 does not necessarily have to be disposed so as to contact the bottom plate of the crucible 3, and may be disposed so that crystal growth starts from the polycrystalline silicon lump 1. .
(Polycrystalline silicon ingot)
The polycrystalline silicon ingot of the present embodiment is manufactured by the polycrystalline silicon ingot manufacturing method of the present embodiment. The polycrystalline silicon ingot of the present embodiment is characterized by the structure of the crystal grains because it is partially epitaxially grown from a polycrystalline silicon block having an average crystal grain size of 15 mm or less. FIG. 5 is a schematic diagram showing the state of the crystalline state at the boundary portion in the vicinity of the interface between the polycrystalline silicon lump serving as the nucleus of crystal growth and the polycrystalline silicon grown thereon. As is clear from FIG. 5, when the cross section of the interface portion is observed, discontinuity exists in the crystal structure at the interface portion. This is because crystals having the same orientation do not necessarily grow epitaxially with respect to all the crystal grains of the polycrystalline silicon block.

  Even in a conventional polycrystalline silicon ingot, each crystal grain does not grow in the same crystal orientation. For example, a discontinuity may occur in the crystal structure at the Σ3 grain boundary due to the deviation of the (111) plane. However, in this case, since it occurs independently in each crystal grain, discontinuity does not occur over a wide region, which is clearly different from the polycrystalline silicon ingot of the present invention.

  In addition, when compositional supercooling occurs in the course of crystal growth, fine silicon crystal nuclei are generated in the liquid phase and adhere to the surface of the already grown crystal grain regardless of the crystal grain orientation. In this case, discontinuity is confirmed in the crystal structure over a wide region where the compositional supercooling condition is satisfied, but this case is also clearly different from the polycrystalline silicon ingot of the present invention.

Therefore, in the polycrystalline silicon ingot of the present embodiment, the discontinuity of the crystal structure at the interface part (boundary part) is not caused by the above-described Σ3, but is also caused by the above-described compositional open cooling. not.
(Polycrystalline silicon block)
The polycrystalline silicon block of the present embodiment can be obtained by processing the polycrystalline silicon ingot of the present embodiment.

  The polycrystalline silicon block is obtained by cutting a surface portion where impurities such as a crucible material may be diffused in the polycrystalline silicon ingot of the present embodiment using a known apparatus such as a band saw. be able to.

Moreover, you may grind | polish the surface of a polycrystalline silicon block as needed.
(Polycrystalline silicon wafer)
The polycrystalline silicon wafer according to the present embodiment can be obtained by processing the polycrystalline silicon block according to the present embodiment.

  The polycrystalline silicon wafer can be obtained, for example, by slicing the polycrystalline silicon block of the present embodiment to a desired thickness using a known apparatus such as a multi-wire saw. At present, a thickness of about 170 to 200 μm is generally used, but the tendency is to reduce the thickness for cost reduction.

Further, if necessary, the surface of the polycrystalline silicon wafer may be polished.
(Polycrystalline silicon solar cell)
The polycrystalline silicon solar cell of the present embodiment is manufactured using the polycrystalline silicon wafer of the present embodiment.

  A polycrystalline silicon solar cell can be manufactured by the well-known solar cell process using the polycrystalline silicon wafer of this Embodiment, for example. That is, in the case of a silicon wafer doped with a p-type impurity by a known method using a known material, an n-type impurity is doped to form an n-type layer to form a pn junction, and the surface electrode And a back surface electrode is formed and a polycrystalline silicon solar cell is obtained. Similarly, in the case of a silicon wafer doped with an n-type impurity, a p-type impurity is doped to form a p-type layer to form a pn junction, and a surface electrode and a back electrode are formed to form a polycrystalline silicon solar A battery cell is obtained. Alternatively, in addition to those using pn junctions between silicon, MIS type solar cells in which a metal is vapor-deposited with a thin insulating layer interposed therebetween, for example, a silicon thin film of an amorphous type having a conductivity type opposite to a polycrystalline silicon wafer, etc. There are films formed and utilizing p-type and n-type silicon heterojunctions having different structures. Further, a plurality of them are electrically connected to obtain a polycrystalline silicon solar cell module.

  As described above, in this specification, the concept including “solar battery cell” and “solar battery module” is simply referred to as “solar battery”. Therefore, for example, what is described as “polycrystalline silicon solar cell” is meant to include “polycrystalline silicon solar cell” and “polycrystalline silicon solar cell module”.

Hereinafter, examples and comparative examples will be described more specifically, but the present invention is not limited to these examples.
(Examples 1 to 10) Study on average crystal grain size of polycrystalline silicon lump Graphite crucible base 6 (880 mm × 880 mm × thickness 200 mm) in the polycrystalline silicon ingot manufacturing apparatus shown in FIG. An outer crucible 5 (inner dimensions: 900 mm × 900 mm × height 460 mm, bottom plate thickness and side wall thickness 20 mm) is installed, and quartz crucible 3 (inner dimensions: 830 mm × 830 mm × 420 mm, bottom plate thickness and side surfaces) A wall thickness of 22 mm) was installed. Further, thermocouples for temperature measurement were installed at two locations near the center of the bottom surface of the crucible 3 and near the center of the bottom surface of the outer crucible 5.

  Next, the polycrystalline silicon lump 1 of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, and Example 10 was added to the crucible 3. After charging the crucible 3 with 420 kg of raw silicon 4 whose boron dopant concentration was adjusted so that the specific resistance of the ingot was about 1.5 Ωcm, the inside of the apparatus was evacuated and argon gas was used. Replaced. Thereafter, the silicon raw material is melted using a heating mechanism (graphite heater 12), and after heating until the polycrystalline silicon lump 1 disposed on the bottom plate is partially melted, cooling from the lower side of the crucible 3 is started, (3) Unidirectional solidification was performed from below to above to grow polycrystalline silicon 4. Thereafter, annealing was performed at about 1200 ° C. for 2 hours, the temperature was lowered at a cooling rate of 100 ° C./hour, and the polycrystalline silicon ingot was taken out from the apparatus. Note that. The polycrystalline silicon lump 1 used in Examples 1 to 10 is a direction parallel to the bottom surface from the bottom portion of the polycrystalline silicon ingot obtained by unidirectionally solidifying the silicon melt from the bottom to the top by a casting method. (Ingot height direction) of about 13 mm thickness was used. As a comparative example, the polycrystalline silicon lump 1 was completely melted, and other than this, a polycrystalline silicon ingot was produced in the same manner as in Examples 1 to 10 above.

  Each of the polycrystalline silicon ingots of Examples 1 to 10 and Comparative Example obtained as described above is processed into a block (156 mm × 156 mm × 220 mm) using a band saw, and further sliced using a wire saw. From each polycrystalline silicon ingot, about 16,000 polycrystalline silicon wafers (156 mm × 156 mm × thickness 0.18 mm) were obtained.

  The obtained polycrystalline silicon wafer was put into a normal solar cell process to produce 16,000 solar cells per ingot, and the output (W) was measured.

  Each solar cell was classified into ranks 1 to 3 as follows from the high output side, and the existence ratio (%) was calculated for each ingot.

Rank 1: Output 100 or more (Standardized by setting the lower limit output of rank 1 to 100)
Rank 2: Output 93 to less than 100 Rank 3: Output less than 93 The results obtained are shown in Table 1 and FIG.

  As is apparent from Table 1 and FIG. 7, in the range of this example, the smaller the average crystal grain size of the polycrystalline silicon lump, the higher the incidence of high-rank products (high output products) and the better the ingot quality. I know that there is.

  When the average crystal grain size of the polycrystalline silicon block was smaller than 15 mm, a slightly better result was obtained than the comparative example in which unidirectional solidification was started after complete melting. It was equivalent to the example and no effect was seen. Therefore, better results than the comparative example were obtained when the average crystal grain size of the polycrystalline silicon block was in the range of 0.1 mm to 15 mm. Even better results are obtained when the average crystal grain size is 8.6 mm or less. If the average crystal grain size is 0.1 mm or more, 5.2 mm or less, 3.1 mm or less, 2 mm or less, 1 mm or less, 0.3 mm or less. The smaller the value, the better the result.

  By using solar cells with good output, good characteristics can be obtained even in a solar cell module in which a plurality of them are arranged.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 polycrystalline silicon lump 2 silicon raw material 3 crucible 4 polycrystalline silicon

Claims (5)

  A polycrystalline silicon lump with an average crystal grain size of 15 mm or less is placed on the upper surface of the crucible bottom plate, and then the silicon raw material is put into the crucible, and the injected silicon raw material is melted and then unidirectionally solidified to form a polycrystalline silicon ingot. A method for producing a polycrystalline silicon ingot.   The method for producing a polycrystalline silicon ingot according to claim 1, wherein at least a part of the polycrystalline silicon ingot is used as the polycrystalline silicon lump.   The method for producing a polycrystalline silicon ingot according to claim 1, wherein the polycrystalline silicon ingot is a bottom of a polycrystalline silicon ingot obtained by unidirectional solidification of a silicon melt.   Using the polycrystalline silicon ingot produced by the polycrystalline silicon ingot producing method according to any one of claims 1 to 3, an application selected from a polycrystalline silicon block, a polycrystalline silicon wafer, and a solar cell is obtained. Manufacturing method for use of polycrystalline silicon ingot.   A polycrystalline silicon ingot that is unidirectionally solidified and includes a boundary portion including a plurality of portions in which grain boundaries are discontinuous in the direction of unidirectional solidification.

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