JP2004277239A - Method for manufacturing plate-like silicon, plate-like silicon, and solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate-like silicon having stable quality and containing gallium at a low cost, and a solar battery which scarcely causes deterioration in characteristics at a low cost by manufacturing it by using the plate-like silicon, and to contribute to the avoidance of environmental problems. <P>SOLUTION: The segregation of gallium is avoided and properties such as specific resistance are stabilized by bringing a silicon melt containing gallium into contact with a substrate and growing a plate-like silicon on the surface of the substrate. It becomes possible to inexpensively manufacture the plate-like silicon because the plate-like silicon does not need a process such as slicing. Further, it becomes possible to supply an inexpensive solar battery by utilizing such a plate-like silicon for the solar battery, and accordingly, to reduce the load on environment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing plate silicon, a plate silicon, and a solar cell. More specifically, the present invention relates to a method for manufacturing plate silicon, which is often used especially for solar cells, a plate silicon, and a solar cell manufactured therefrom.
[0002]
[Prior art]
Recently, solar cells are expected as clean energy. Among them, polycrystalline silicon solar cells occupy the largest ratio for achieving both cost and performance. However, in order to spread the solar cell more widely, it is necessary to further reduce the cost of the solar cell per unit generated power.
Many conventional silicon solar cells use polycrystalline silicon. This solar cell is generally manufactured by diffusing phosphorus, which is an N-type dopant, onto the surface of a P-type polycrystalline silicon substrate containing boron as a dopant to form a PN junction. Here, the polycrystalline silicon substrate used is generally a cast method produced by melting silicon in a crucible and gradually cooling it.
[0003]
However, in recent years, it has been suggested that the cause of the deterioration of the characteristics of the solar cell is related to the formation of a complex of boron as a dopant and oxygen contained in the crystal. Therefore, for example, Japanese Patent Application Laid-Open No. 2001-64007 (Patent Document 1) proposes a method of using gallium as a P-type dopant to suppress deterioration in characteristics of a solar cell. As a method for manufacturing such a wafer, there has been proposed a method in which gallium-added silicon is melted, a melt is cooled to produce a polycrystalline silicon ingot, and the ingot is cut or sliced.
[0004]
However, the segregation coefficient of gallium 0.008 is two orders of magnitude smaller than the segregation coefficient of boron of 0.8, and when an ingot is manufactured as described above, gallium is not incorporated into the crystal in the early stage of growth, and the melt gradually melts. And gallium uptake increases as growth progresses. For this reason, the resistivity distribution in the ingot is large, and it is difficult to supply a wafer of stable quality. Manufacturing an ingot having a small resistivity distribution leads to an increase in cost.
[0005]
Such segregation can be suppressed to some extent by increasing the cooling rate, that is, the growth rate of the silicon crystal. When the growth rate of the silicon crystal is low, the probability of introduction of {111} stacking faults, twin grain boundaries, etc. is low, and a crystal close to a single crystal grows from a crystal nucleus generated on the crucible wall, and from the crucible wall. As the distance increases, crystals are removed, and large crystal grains are formed.
[0006]
On the other hand, when the growth rate is increased as described above, as the crystal nuclei grow, many {111} stacking faults and twin grain boundaries are introduced. It is known that stacking faults on the {111} plane, twin grain boundaries, and the like do not affect solar cell characteristics. However, when defects such as stacking faults and twin boundaries are introduced into different {111} planes of one crystal, a substantially random grain boundary is generated from a line where two plane defects intersect, and This is a defect that affects the characteristics of the battery. As the silicon crystal grown from one crystal nucleus grows away from the crucible wall, substantial random grain boundaries increase, and an ingot of large crystal grains as obtained by slow cooling cannot be obtained.
[0007]
Japanese Patent Application Laid-Open No. 2002-68724 (Patent Document 2) proposes a method of suppressing the influence of gallium segregation on grain boundaries by setting the crystal grain size of polycrystalline silicon to 2 mm or more. . However, the effect of gallium segregation is more of a problem in large variations in crucible size than in local differences such as grain boundaries and intragranules. Is difficult to control.
[0008]
In Japanese Patent Application Laid-Open No. Hei 6-191820 (Patent Document 3), as a method for manufacturing a silicon thin plate, an interface between a melt of indium, tin, and gallium in which silicon is dissolved and a gaseous phase is made non-melt. A method has been proposed in which a thin plate of silicon is deposited by cooling using a cooler arranged so as to be in contact. However, with such a method, it is difficult to control the silicon concentration in the melt, and mass production is difficult. In addition, it is difficult to control the concentration of indium, tin, and gallium incorporated as impurities in silicon.
[0009]
On the other hand, in Japanese Patent Application Laid-Open No. 2001-223172 (Patent Document 4), a cooled substrate surface is brought into contact with a melt containing at least one of a metal and a semiconductor, and crystals of the melt material are exposed to the surface of the substrate. There has been proposed a method of directly growing a plate-like body by growing the plate-like body. By applying this method to silicon, the steps of cutting a block from an ingot and slicing a wafer from a block as in the conventional casting method can be eliminated. For this reason, the method is a method that eliminates the loss of the raw material as a margin and eliminates the cost for the above-mentioned steps, thereby making it possible to produce plate-like silicon at low cost. In addition, this method is applicable to mass production because the growth rate of the plate-like body is high.
[0010]
[Patent Document 1]
JP 2001-64007 A
[Patent Document 2]
JP-A-2002-68724
[Patent Document 3]
JP-A-6-191820
[Patent Document 4]
JP 2001-223172 A
[0011]
[Problems to be solved by the invention]
For example, when manufacturing a solar cell, it is desirable to provide a low-cost solar cell with less characteristic deterioration and to provide gallium-containing plate-like silicon with more stable quality at a low cost in order to reduce the burden on the environment. It is rare.
[0012]
[Means for Solving the Problems]
The present inventors have made intensive studies and found that the above problem can be solved by bringing a silicon melt containing gallium into contact with a substrate and growing plate-like silicon on the substrate surface, thereby completing the present invention. Reached.
[0013]
Thus, according to the present invention, there is provided a method for producing plate-like silicon, which comprises contacting a gallium-containing silicon melt with a substrate to grow gallium-containing plate-like silicon on the substrate surface.
[0014]
Further, according to the present invention, there is provided a plate-shaped silicon produced by the above method.
[0015]
Further, according to the present invention, there is provided a solar cell produced using the above-mentioned plate-like silicon.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for producing gallium-containing plate silicon of the present invention is characterized in that a silicon melt containing gallium is brought into contact with a substrate to grow plate silicon on the substrate surface. The gallium concentration in the plate-like silicon can be appropriately adjusted according to the use in which the plate-like silicon is used. For example, when plate silicon is used for a solar cell, the gallium concentration in the crystal is 1E15 atoms / cm. ³ From 1E17 atoms / cm ³ The degree is general, more preferably 5E15 atoms / cm ³ ~ 3E16 atoms / cm ³ It is.
[0017]
(Production equipment for gallium-containing plate silicon)
FIG. 1 shows an example of an apparatus capable of implementing the method for producing gallium-containing plate-like silicon of the present invention, and the present invention will be described based on the drawing. However, the apparatus for obtaining the plate-like silicon of the present invention is not limited to this.
In FIG. 1, reference numeral 12 denotes the obtained gallium-containing plate-like silicon, 11 denotes a substrate, 13 denotes a crucible, 14 denotes a gallium-containing silicon melt, 15 denotes a heater for heating, 16 denotes a crucible base, 17 denotes a heat insulating material, and 18 denotes a crucible. The elevating table 19 is a shaft fixed to the substrate. However, in this figure, the means for moving the substrate 11, the means for raising and lowering the crucible table 16, the means for controlling the heater for heating, the means for additionally adding silicon, and the outside of the apparatus such as a chamber capable of vacuum evacuation are described. Not listed.
[0018]
In addition, 13 to 19 are installed in a chamber having good airtightness, and need to have a structure that can be replaced with an inert gas or the like after evacuation. At this time, argon, helium, or the like can be used as the inert gas, but argon is more preferable in consideration of cost. Furthermore, constructing a circulation type system leads to lower cost. In addition, when a gas containing an oxygen component is used, silicon oxide is generated and attached to a substrate surface or a chamber wall. Therefore, it is preferable to remove the oxygen component as much as possible. Further, even when a gas circulation system is used, it is preferable to remove silicon oxide particles through a filter or the like.
[0019]
As shown in FIG. 1, the substrate 11 having a temperature equal to or lower than the silicon melt temperature enters the gallium-containing silicon melt 14 in the crucible 13 from the left side in the figure and is immersed in the gallium-containing silicon melt 14. At this time, the gallium-containing silicon melt is held by the heating heater 15 at a temperature equal to or higher than the melting point. In order to obtain stable plate-like silicon, it is preferable that the apparatus be configured so that the temperature of the melt can be controlled, the temperature of the atmosphere in the chamber, and the temperature of the substrate 11 can be strictly controlled. With such an apparatus configuration, gallium-containing plate-like silicon can be obtained with higher reproducibility.
[0020]
It is preferable that the substrate be provided with a structure whose temperature can be easily controlled. The material of the substrate is not particularly limited, but is preferably a material having good heat conductivity or a material having excellent heat resistance. For example, high-purity graphite, silicon carbide, quartz, boron nitride, alumina, zirconium oxide, aluminum nitride, metal, and the like can be used, but an optimum material may be selected according to the purpose. High-purity graphite is more preferable because it is relatively inexpensive and is a material with high workability. The material of the substrate can be appropriately selected in view of various industrial properties such as low cost of the substrate and the quality of the obtained plate-like silicon such as the substrate quality. Further, when a metal is used for the substrate, there is no particular problem as long as the metal is used at a temperature lower than the melting point of the substrate, for example, the cooling is always performed, and the characteristics of the obtained sheet are not significantly affected.
[0021]
In order to facilitate the temperature control of the substrate 11, it is convenient to use a copper fixed substrate. The fixed substrate refers to a portion connecting the shaft 19 fixed to the substrate and the substrate 11, and is not illustrated here. The cooling means for the fixed substrate and the substrate 11 can be roughly classified into two types, that is, direct cooling and indirect cooling. Direct cooling is a means for cooling by blowing a gas directly on the substrate, and indirect cooling is a means for indirectly cooling the substrate with a gas or liquid. The type of the cooling gas is not particularly limited, but it is preferable to use an inert gas such as nitrogen, argon, helium, or the like for the purpose of preventing oxidation of the plate-like silicon. Particularly, helium or a mixed gas of helium and nitrogen is preferable in consideration of the cooling capacity, but nitrogen is preferable in consideration of the cost. By circulating the cooling gas using a heat exchanger or the like, the cost can be further reduced, and as a result, inexpensive gallium-containing silicon plate can be provided.
[0022]
Further, it is preferable to have a mechanism for heating the substrate 11. That is, the temperature of the substrate 11 is preferably not only provided with a cooling mechanism but also provided with a heating mechanism. In the substrate 11 immersed in the gallium-containing silicon melt, gallium-containing plate-like silicon grows on the substrate surface. Thereafter, the substrate 11 is discharged from the melt, but the side of the substrate 11 facing the melt receives heat from the gallium-containing silicon melt, and the temperature of the substrate tends to increase. However, when the substrate is subsequently immersed in the gallium-containing silicon melt at the same temperature, a cooling mechanism for lowering the temperature of the substrate is required. However, even with direct cooling or indirect cooling, it is difficult to control the cooling rate, that is, the substrate temperature at any time. Therefore, it is preferable to provide a heating mechanism.
[0023]
That is, the substrate once escaped from the gallium-containing silicon melt is cooled by a cooling mechanism, and it is better to control the temperature of the substrate by using a heating mechanism before being immersed in the gallium-containing silicon melt. . The heating mechanism may be a high-frequency induction heating method or a resistance heating method. However, the condition is that the heating heater for maintaining the molten state of the gallium-containing silicon is not affected. As described above, by using the cooling mechanism and the heating mechanism together, the reproducibility of the characteristics of the gallium-containing plate-like silicon is remarkably improved.
[0024]
What is important together with the temperature control of the substrate is the temperature control of the gallium-containing silicon melt. If the temperature of the melt is set near the melting point, the surface of the silicon may solidify when the substrate comes into contact with the melt. Therefore, the temperature of the melt is preferably equal to or higher than the melting point. This is preferably strictly controlled using a plurality of thermocouples or radiation thermometers.
[0025]
To strictly control the temperature of the melt, it is straightforward to immerse the thermocouple in the melt, but this is not preferred because impurities from the protection tube or the like of the thermocouple are mixed into the melt. It is preferable that the control part has a structure in which the temperature can be controlled indirectly by inserting a thermocouple into a crucible or the like, or the temperature of the gallium-containing silicon melt can be controlled by a radiation thermometer.
[0026]
The crucible 13 containing the melt is placed on a heat insulating material 17. A crucible table 16 is provided on the heat insulating material 17. The crucible table 16 is connected to a crucible elevating table 18 and needs to be provided with an elevating mechanism. This is because the gallium-containing plate-like silicon is grown on the substrate 11 so that the substrate 11 is always moved up and down so that it can be immersed in the gallium-containing silicon melt 14 at the same depth.
[0027]
In addition, as a method of keeping the level of the molten metal surface constant, that is, a method of replenishing the silicon extracted from the gallium-containing silicon melt as the gallium-containing plate-shaped silicon and the silicon lost as vapor, a polycrystalline silicon is used. It is possible to use a method in which the (mass) is melted and charged, a method in which the molten liquid is sequentially charged, a method in which the powder is sequentially charged, and the like, but a method of keeping the molten metal surface position constant is not particularly limited. However, it is preferable not to disturb the molten metal surface as much as possible. When the melt surface is disturbed, the wave shape generated at that time is reflected on the melt surface side of the obtained gallium-containing plate-shaped silicon, which may impair the uniformity of the shape of the obtained plate-shaped silicon. That's why.
[0028]
As a means for heating the melt, a high-frequency induction coil may be used instead of the heater 15 for heating. In this case, the charge in the gallium-containing silicon melt is heated by the action of receiving a high frequency magnetic field from the coil. By finding in advance the correlation between the gallium concentration in the melt and the high-frequency power required to maintain the melt temperature constant as an empirical value, by comparing with the value of the high-frequency power in the production of plate silicon, It is also possible to estimate the gallium concentration in the silicon melt, and fine-grained production control can be performed.
[0029]
The apparatus for producing plate-like silicon according to the present invention is not limited to the above-described apparatus, and it is sufficient that the rate of crystal growth from the melt is so high that segregation of gallium does not occur. For example, a manufacturing apparatus such as a liquid phase epitaxial growth apparatus, a zone melting recrystallization apparatus, and a laser melting recrystallization apparatus may be used.
[0030]
(Production method of gallium-containing plate-shaped silicon)
Next, an example of the method for producing gallium-containing plate silicon according to the present invention using the gallium-containing plate silicon production apparatus shown in FIG. 1 will be described.
First, a crucible 13 made of high-purity graphite is filled with a silicon raw material in which the concentration of gallium is adjusted so that the specific resistance of the obtained plate-like silicon becomes a desired concentration until the crucible 13 becomes full. The crucible is set in an apparatus as shown in FIG. Next, the chamber is evacuated to reduce the pressure in the chamber to a predetermined pressure. After that, Ar gas is introduced into the chamber, and Ar gas is kept flowing from the upper portion of the chamber at a constant rate of 10 L / min. The reason why the gas is continuously supplied is to obtain a clean silicon surface.
[0031]
Next, the temperature of the heater 15 for melting silicon is set to 1500 ° C., and the silicon mass in the crucible 13 is completely melted. At this time, since the silicon raw material is melted to lower the liquid level, new silicon powder is introduced so that the molten metal surface of the gallium-containing silicon melt is at a position 1 cm below the upper surface of the crucible 13. It is preferable that the silicon melting heater is not heated up to 1500 ° C. at a time, but is heated up to about 1300 ° C. at a heating rate of 10 to 50 ° C./min, and then raised to a predetermined temperature. This is because when the temperature is rapidly increased, thermal stress is intensively applied to the corners of the crucible and the like, leading to breakage of the crucible.
[0032]
Thereafter, the temperature of the gallium-containing silicon melt is set at 1410 ° C., and the temperature is maintained for 30 minutes to stabilize the melt temperature, and the crucible 13 is moved to a predetermined position using the crucible elevating table 18. The temperature of the gallium-containing silicon melt at this time is preferably 1400 ° C. or more and 1450 ° C. or less. This is because the melting point of silicon is around 1410 ° C., and if it is set to 1400 ° C. or less, the molten metal surface gradually solidifies from the crucible wall. On the other hand, when the temperature is set higher than 1450 ° C., the growth rate of gallium-containing plate-like silicon becomes slow, and gallium segregates due to gallium segregation, which is not preferable.
[0033]
Next, gallium-containing plate-like silicon is grown, and a substrate having a shape suitable for use, for example, a rectangular parallelepiped substrate is moved from left to right in the direction of the arrow in FIG. At this time, the substrate is moved so that the surface of the substrate comes into contact with the gallium-containing silicon melt. Thus, plate-like silicon grows on the surface of the substrate. The trajectory for producing the plate-like silicon on the substrate may be the trajectory shown in FIG. 1, or may be a circular trajectory or an elliptical trajectory. In particular, a structure that can realize an arbitrary trajectory is preferable.
[0034]
The substrate temperature when entering the gallium-containing silicon melt is preferably 200 ° C. or more and 900 ° C. or less. If the substrate temperature is 200 ° C. or lower, stable control becomes difficult. That is, in the case of continuous production, in a chamber, a substrate waiting for immersion receives radiant heat from a gallium-containing silicon melt, and it is difficult to constantly maintain the temperature at 200 ° C. or lower, and the quality of the obtained gallium-containing plate-like silicon varies. This leads to the occurrence of On the other hand, when the temperature of the substrate is 900 ° C. or higher, the growth rate of gallium-containing plate-like silicon becomes slow, and gallium tends to segregate on the melt side. As described above, the obtained plate-shaped silicon tends to vary depending on the temperature of the substrate. Therefore, it is preferable to provide both the cooling mechanism and the heating mechanism. A more preferred substrate temperature is 300 to 700 ° C.
[0035]
As described above, in order to improve the product yield and stabilize the quality, it is preferable to make the temperature control as strict as possible.
Further, the contact time between the silicon melt containing gallium and the substrate is preferably within 10 seconds. At higher temperatures, the temperature of the plate-like silicon itself grown on the substrate also rises, and the gallium incorporated in the crystal flows out into the melt due to diffusion.If the growth rate is slow, the gallium moves toward the melt due to segregation. Is concentrated.
Further, the growth rate of the gallium-containing plate-shaped silicon in the thickness direction is desirably 0.03 mm / sec or more. This is also because if the growth rate is low, gallium is concentrated on the melt side due to segregation of gallium. A more preferred growth rate is 0.05 to 0.3 mm / sec.
[0036]
The method for producing plate-like silicon of the present invention is not limited to the method described above, and it is sufficient that the rate of crystal growth from the melt is so high that gallium segregation does not substantially occur. For example, a method such as a liquid phase epitaxial growth method, a zone melting recrystallization method, and a laser melting recrystallization method may be used.
Further, the plate thickness of the plate-like silicon is preferably 1 mm or less, more preferably 0.1 mm or more and 1 mm or less. If the plate thickness is larger than 1 mm, segregation of gallium cannot be ignored. Further, when the plate thickness is 0.1 mm or more, the yield due to frequent occurrence of cracks or chipping of the plate-like silicon in the solar cell manufacturing process can be suppressed, which is preferable.
[0037]
The plate-like silicon of the present invention is characterized in that gallium segregation is small. A large amount of segregation can be evaluated by measuring the specific resistance of the silicon plate. Specifically, the smaller the variation in the specific resistance, the smaller the segregation. In the present invention, the variation in the specific resistance can be suppressed within a range of ± 0.5Ω, although it varies depending on the manufacturing conditions. The specific resistance of the plate-like silicon formed by the conventional casting method usually varies in the range of -0.8 to + 9Ω, and it is understood that the plate-like silicon of the present invention has less gallium segregation.
[0038]
The plate-like silicon of the present invention can be used in various fields such as solar cells and semiconductor devices. Of these, it is preferable to use it as a raw material for a solar cell. The plate-like silicon of the present invention can be used for a solar cell by, for example, the following method. That is, the plate-like silicon is cut into a predetermined size as necessary, and then n-type impurities such as phosphorus and arsenic are diffused. This diffusion forms a pn junction in the silicon plate.
[0039]
Next, a solar cell can be obtained by forming a front electrode and a back electrode so as to sandwich the plate-like silicon by, for example, a vapor deposition method, a coating / firing method, or the like. In addition, if necessary, p-type silicon may be added to the plate-like silicon on the back electrode side. ⁺ A layer may be formed.
[0040]
【Example】
Example
(Production of gallium-containing plate silicon)
A silicon raw material whose gallium concentration was adjusted to have a specific resistance of 1 Ω · cm was put in a quartz crucible protected by a high-purity carbon crucible and fixed in the chamber shown in FIG.
[0041]
First, 10 ^-5 It was evacuated to about torr and replaced with Ar gas at normal pressure. Thereafter, Ar gas was introduced into the chamber, and the pressure was returned to normal pressure. Thereafter, Ar gas was constantly flowed from the upper part of the chamber at 2 L / min. Next, the silicon raw material was melted by the heater. The temperature of the silicon melting heater was raised to 1500 ° C. at a rate of 10 ° C./min. After confirming that the silicon raw material was completely dissolved, the temperature of the crucible was maintained at 1425 ° C. for stabilization.
[0042]
Next, the high-purity carbon substrate 11 having the shape shown in FIG. 2A was heated to 600 ° C. by high-frequency heating. Thereafter, the plate-like silicon growth surface 20 was turned to the melt side, and immersed in the melt to a depth of 5 mm to grow gallium-containing plate-like silicon. The contact time between the substrate and the melt was about 5 seconds. FIG. 2B is a schematic perspective view of the shape of the obtained gallium-containing plate-like silicon. The obtained gallium-containing plate-like silicon had an average thickness of about 0.32 mm, and could be easily separated from the substrate.
[0043]
This process was repeated 100 times, and when 100 gallium-containing plate-like silicon were obtained, a raw material corresponding to the reduced amount of the melt was additionally introduced into the crucible. This was repeated 10 times to obtain a total of 1000 gallium-containing plate-like silicon. When their specific resistances were measured, they were between 0.8Ω and 1.5Ω. From these results, it was determined that gallium-containing plate-like silicon was obtained, in which gallium segregation did not occur during the growth of plate-like silicon, the variation in gallium concentration was small, and the quality was stable. In the present manufacturing method, the growth rate of gallium-containing plate silicon is high and segregation is unlikely to occur, and thus it is considered that gallium-containing plate silicon with stable resistivity was thus produced.
[0044]
Further, when the thickness of the gallium-containing plate-like silicon is 1 mm or less as in this embodiment, there is an advantage that the time required for growth is short and gallium is unlikely to segregate. In addition, as described above, as the distance from the crystal nucleus increases, the possibility of encountering a plurality of stacking faults and twin grain boundaries introduced into the crystal grown from one crystal nucleus increases, substantially reducing the solar cell characteristics. Random grain boundaries increase. When the thickness of the gallium-containing plate-like silicon is 1 mm or less, there is almost no possibility that a plurality of stacking faults or twin grain boundaries will be met, and the gallium-containing silicon is suitable as a substrate for manufacturing a solar cell.
[0045]
(Production of solar cell)
Next, a solar cell was manufactured using the obtained gallium-containing plate-shaped silicon. The obtained gallium-containing plate silicon was cut with a laser, and a 50 mm × 50 mm gallium-containing plate silicon was taken out. Next, etching and cleaning were performed with a mixed solution of nitric acid and hydrofluoric acid. Thereafter, alkali etching was performed using sodium hydroxide. After that, POCl ₃ By diffusion, n ⁺ A layer was formed. The PSG (phosphorus glass) film formed on the plate-like silicon surface was removed with hydrofluoric acid.
[0046]
Thereafter, a silicon nitride film was formed on the n-layer on the light receiving surface side of the solar cell by using a plasma CVD apparatus. Next, n which is also formed on the surface which is to be the back surface side of the solar cell ⁺ The layer was removed by etching with a mixed solution of nitric acid and hydrofluoric acid. Next, an aluminum paste was applied to the surface to be the back surface by screen printing. By firing, the back electrode and p ⁺ Layers were formed simultaneously. Next, an electrode pattern was formed on the light receiving surface side using screen printing by using silver paste. Then, the silver electrode is formed by baking, and at the same time, the silver electrode and n ⁺ Conduction with the layers was established. Thereafter, a solar cell was manufactured by performing solder dip on the silver electrode portion.
[0047]
The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”.
The measurement results show that the average short-circuit current of the completed cell was 31.12 (mA / cm). ² ), Open-circuit voltage 590 (mV), fill factor 0.755, and efficiency 13.86 (%).
[0048]
Next, deterioration of characteristics of the solar cell manufactured as described above was examined. As a result, the solar cell was kept irradiated with AM1.5 light for 30 hours while maintaining the temperature of the solar cell in an open state in which both electrodes were not connected to a load at 30 ° C. under a solar simulator under a solar simulator, and then again. When the conversion efficiency was measured, the conversion efficiency was 13.86 (%), which was the same as before the light irradiation within the measurement error range, and it was confirmed that there was almost no characteristic deterioration.
[0049]
Comparative example
In this comparative example, an example in which gallium-containing plate-shaped silicon is manufactured by a casting method that is generally used for manufacturing polycrystalline silicon is shown. The casting method is a method in which silicon is melted in a crucible and the melt is cooled to produce a silicon ingot. In order to manufacture a solar cell wafer from the ingot manufactured by this method, it is necessary to first cut out the ingot into blocks using a band saw, and then slice each block into wafers using a wire saw. Several tens of percent of the raw material charged in this process is wasted as cutting margin.
[0050]
Here, it is assumed that gallium is uniformly doped in silicon in a quartz crucible having a diameter of 20 cm and a depth of 30 cm. After slow cooling, a columnar gallium-containing polycrystalline silicon ingot was produced. The crucible was cooled by pulling the crucible downward from the heating area at a rate of 0.05 mm / min.
When the distribution of the specific resistance of the gallium-containing polycrystalline silicon ingot thus grown was measured in the vertical direction, it changed almost continuously from 10Ω to 0.2Ω, and a stable quality solar cell was produced. It was difficult to do.
[0051]
It should be understood that the embodiments and examples disclosed this time are examples of all points and are not restrictive. 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. Although the manufacturing apparatus shown in FIG. 1 has been described as an example, the manufacturing apparatus is not particularly limited as long as it can grow gallium-containing plate-like silicon on the substrate by bringing the melt into contact with the substrate. Further, as an example of the shape of the substrate to be brought into contact with the melt, the shape shown in FIG. 2A is given, but the shape is not particularly limited.
[0052]
【The invention's effect】
By using the method for producing gallium-containing plate silicon of the present invention, gallium-containing plate silicon of stable quality can be provided at low cost. Further, by manufacturing a solar cell from the plate-like silicon, a solar cell with less characteristic deterioration can be provided at low cost, and it is possible to contribute to avoiding environmental problems.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of a manufacturing apparatus for manufacturing a gallium-containing plate-like silicon of the present invention.
FIG. 2A is a schematic perspective view of an example of a growth substrate for growing gallium-containing plate silicon, and FIG. 2B is a schematic perspective view of the grown gallium-containing plate silicon.
[Explanation of symbols]
11 Substrate
12 Gallium-containing plate silicon
13 crucible
14 Gallium-containing silicon melt
15. Heating heater
16 crucible stand
17 Insulation
18 Crucible lifting table
19 Shaft fixed to the substrate
20 Plate-like silicon growth surface
21 Gallium-containing plate silicon

Claims (10)

A method for producing plate-like silicon, comprising contacting a gallium-containing silicon melt with a substrate to grow gallium-containing plate-like silicon on the substrate surface. 2. The method of claim 1, wherein a relative position between the substrate and a container holding the silicon melt is changed with time during the growth of the silicon plate on the substrate surface. 3. 3. The method for producing plate-like silicon according to claim 1, wherein when the substrate is brought into contact with the silicon melt, the substrate is maintained at a temperature in a range of 200 to 900 ° C. 4. The method according to any one of claims 1 to 3, wherein when the substrate is brought into contact with the silicon melt, the silicon melt is maintained at a temperature in a range of 1400 to 1450 ° C. . The method according to claim 1, wherein a contact time between the silicon melt and the substrate is within 10 seconds. The method for producing plate-shaped silicon according to any one of claims 1 to 5, wherein the gallium-containing plate-shaped silicon grows at a rate in a plate thickness direction of 0.03 mm / sec or more. The method for producing plate-like silicon according to any one of claims 1 to 6, wherein the gallium-containing plate-like silicon has a variation in specific resistance within a range of ± 0.5Ω. A plate-like silicon produced by the method according to any one of claims 1 to 7. The plate-like silicon according to claim 8, wherein the plate-like silicon has a thickness of 0.1 to 1 mm. A solar cell manufactured using the plate-shaped silicon according to claim 8.

Images