JP4434837B2 - Solar cell - Google Patents

Description

  The present invention relates to a solar cell, and more particularly to a solar cell in which the manufacturing process is simplified while the surface unevenness is improved.

  In recent years, attention to environmental issues has increased, and expectations for solar cells as clean energy have increased. While the tightness of silicon raw materials is screamed, solar cells using silicon thin films are expected, but at present, those using crystalline silicon are most popular. Among them, in particular, a solar cell manufactured using a polycrystalline silicon substrate is most advantageous in terms of cost performance, and occupies a majority of the solar cell production.

  In general, a crystalline silicon solar cell suppresses reflection on the surface by forming fine irregularities on the crystal surface for the purpose of efficiently capturing incident light into the crystal. For this purpose, anisotropic etching using an alkaline aqueous solution such as NaOH, reactive gas etching (RIE), etching using a mask, V-groove processing by machining, and the like are performed.

  Further, as disclosed in Patent Document 1 below, an attempt is made to improve the design by changing the surface shape pattern within the surface of the solar cell by performing etching with an alkali a plurality of times using a mask. It has been broken.

  As the polycrystalline silicon used in the solar cell, a cast substrate produced by slicing a polycrystalline ingot obtained by pouring a silicon melt into a mold and gradually cooling it is generally used. In addition, an electromagnetic cast substrate manufactured by slicing an ingot melted by a high frequency induction coil and continuously solidified without contact with a crucible by electromagnetic force is used.

  In a substrate manufacturing method that requires a slicing step, such as the cast substrate or electromagnetic cast substrate, it takes material loss, time, and cost when slicing, and as a result, it is difficult to provide a solar cell at a low price. Thus, attempts have been made to grow ribbon-like crystalline silicon directly from a silicon melt. For example, Patent Document 2 below devises such a ribbon-shaped silicon plate manufacturing method.

  However, in the anisotropic etching using an alkaline aqueous solution such as NaOH described above, the surface shape after etching differs depending on the crystal orientation. When a cast substrate, an electromagnetic cast substrate, or the like is etched by this method, one crystal surface becomes a monotonous and repeated shape. In addition, since the shape of adjacent crystal grains is almost the same, reflection differs depending on the size of the crystal grains, and it looks like solar cell unevenness, so some people may feel visually dissatisfied, This is one of the factors that hinder the spread of batteries.

  If the grain size of the crystal grains is reduced, the difference in reflection between the crystal grains is less likely to be noticed, but it is a known fact that the grain boundaries adversely affect solar cell characteristics, which is not preferable from the aspect of characteristics. .

  In the RIE (reactive ion etching) method, fine irregularities can be formed on the surface of the silicon crystal regardless of the crystal orientation, so that unevenness in the solar cell surface is relatively less likely to occur, but the process itself is costly. There is a problem that it takes.

  In the case of etching using a mask, as in RIE, unevenness in the surface of the solar cell is hardly generated, but a process such as photolithography is required, which increases the number of processes and costs.

In addition, the method described in the following Patent Document 1 performed from the viewpoint of improving the design is an attempt to deliberately add in-plane unevenness to design characters and the like, but an etching process using a mask. Is necessary several times, so there is a problem in terms of cost.
JP-A-8-204220 JP 2001-223172 A

  The present invention has been made in order to solve the above-described problems of the prior art, and an object of the present invention is to provide a solar cell having a uniform surface with little unevenness on the surface of the solar cell and good conversion efficiency, and a solar cell. The battery module is supplied at a low price.

  The present invention provides a solar cell using crystalline silicon, wherein the surface shape of one crystal grain on the light incident surface of the crystalline silicon is divided into two or more regions.

  Preferably, the surface shape in the one crystal grain is divided into two or more regions by one anisotropic etching.

  Preferably, the light incident surface of the crystalline silicon is constituted by a (111) plane of the crystalline silicon.

  Preferably, the difference in the uneven shape of the light incident surface is 20 μm or more and 200 μm or less.

  Preferably, the crystalline silicon is produced by bringing a base plate into contact with a silicon melt and growing crystals on the base plate.

  Preferably, the light incident surface is a surface of the crystalline silicon that is in contact with the base plate.

  Preferably, the surface shape is substantially periodic.

  Preferably, the range of the period of the surface shape is 0.5 mm or more and 5.0 mm or less.

  According to the present invention, it is possible to provide a solar cell with less unevenness of the solar cell and good characteristics at a low price.

  The solar cell of the present invention is a solar cell using crystalline silicon, wherein the surface shape in one crystal grain on the light incident surface of the crystalline silicon is divided into two or more regions. provide. By using a solar cell with such a structure, while maintaining a large crystal grain size of silicon, the surface unevenness is divided into regions smaller than the actual crystal grain size, resulting in less unevenness and high conversion efficiency. This is because it is possible to achieve both. Here, the unevenness of the surface of the solar cell complains that there is no visual uniformity due to the different surface shape. Therefore, the surface unevenness complains that there is little visual unevenness when the number of different surface shapes is large and small, while the surface unevenness is visually uneven when the number of different surface shapes is small and large. Appeals that there are many. In the present invention, since the surface shape in one crystal grain is divided into two or more regions, the surface unevenness is small and the appearance of the manufactured solar cell is also good. Here, the crystal grain means a crystal region having the same crystal orientation, and the surface shape means an uneven pattern on the crystal surface.

  In the solar cell of the present invention, it is preferable that the light incident surface of crystalline silicon is composed of a (111) plane of silicon crystal. The reason is that the (111) plane of the silicon crystal is the plane that appears when anisotropic etching of silicon is performed with an alkaline aqueous solution such as NaOH or KOH, and has the best etching controllability. This is because it is suitable for battery production. In the present invention, the etching can be performed by heating an alkaline aqueous solution such as KOH or NaOH to about 90 ° C. and immersing the silicon substrate in the alkaline aqueous solution. The alkaline aqueous solution can be set to a concentration of several% to 10%. Note that isopropyl alcohol is preferably added to the alkaline aqueous solution. This is because the uneven shape becomes finer.

  Moreover, in the solar cell of the present invention, it is preferable that the uneven shape difference on the light incident surface side is 20 μm or more and 200 μm or less. The reason is that if the uneven shape difference is 20 μm or more, the surface unevenness is divided into regions smaller than the actual crystal grain size, and the unevenness is less noticeable, and if it is 200 μm or less, the yield is good. This is because the electrodes can be printed. Further, in the present invention, the difference in the concavo-convex shape can be evaluated by measuring the surface shape with a stylus profilometer, analyzing the maximum value and the minimum value of the height after correcting the inclination.

  In the solar cell of the present invention, the crystalline silicon is preferably produced by bringing a base plate into contact with a silicon melt and growing crystals on the base plate. Here, it is preferable that the light incident surface in the present invention is a surface that is in contact with the base plate during the production of crystalline silicon. The reason for this is that the surface of the plate-like crystalline silicon on the base plate side is considered to grow in a supercooled state, so that roughening is unlikely to occur and a surface with an orientation close to the facet surface is likely to appear. Therefore, even one crystal grain is three-dimensionally surrounded by a plurality of faces (for example, six) close to different facet planes, and is divided into a plurality of patterns when anisotropic etching is performed with an alkaline aqueous solution. Because. One crystal grain is often divided into six regions, which is particularly convenient for achieving both a large crystal grain size that is important from the aspect of solar cell characteristics and a fine surface shape that is important from the viewpoint of unevenness. . Such a feature is a feature that is not found in a silicon substrate that has undergone a slicing process and has a flat surface.

  In the solar cell using the plate-like crystalline silicon of the present invention, the surface shape of the light incident surface is more preferably approximately periodic. This is because the periodic surface shape has better controllability of the crystal grain size and is less likely to cause unevenness in the solar cell surface. Here, “periodic” means that the thickness of the crystalline silicon changes periodically.

  Moreover, the range of the period of the surface shape is desirably 0.5 mm or more and 5.0 mm or less. The reason is that the conversion efficiency of the solar cell is obtained to some extent if it is 0.5 mm or more, and unevenness is less likely to be noticed if it is 5.0 mm or less. In the present invention, the period can be easily evaluated by visual observation or observation with a microscope.

  Next, in order to facilitate understanding of the solar cell of the present invention, FIG. 2 shows a solar cell using a silicon substrate manufactured by a general casting method without using the crystalline silicon in the present invention described above. It explains using.

  FIG. 2 is a schematic view of a portion where no electrode is provided in the light incident surface of the solar cell. However, the antireflection film is not shown. In general solar cells, fine irregularities are formed on the surface on the light incident surface side by anisotropic etching with an alkaline aqueous solution at the time of production. A thick line B in FIG. 2 represents a crystal grain boundary, and G21, G22, and G23 are shown as examples of crystal grains. In the conventional solar cell, the inside of each crystal grain G21, G22, G23 is etched into a shape determined by each crystal orientation, and the surface shape pattern does not change in the crystal grain.

  Therefore, the crystal grain pattern could be confirmed as the unevenness of the solar cell as it was. As the crystal grain size becomes finer, this unevenness is averaged. However, as described above, since the conversion efficiency of the solar cell is lowered when the crystal grain size is reduced, the solar cell is reduced by reducing the crystal grain size. The method of eliminating the unevenness is not realistic.

  On the other hand, the solar cell of this invention is demonstrated using FIG. In the solar cell of the present invention, the surface shape is divided into, for example, six regions in one crystal grain G13, and is not easily recognized as unevenness of the solar cell. It is also possible to ensure the crystal grain size, which is an important factor for the conversion efficiency of the solar cell.

  In the present invention, a known method can be used as a method for manufacturing a solar cell using crystalline silicon as described above.

(Plate silicon production equipment)
An example of a manufacturing apparatus used in the method for manufacturing a plate-like crystalline silicon of the present invention will be described with reference to FIG. However, the apparatus for obtaining the plate-like crystalline silicon of the present invention is not limited to this, and any apparatus that produces plate-like crystalline silicon by bringing the base plate into contact with the silicon melt may be used. FIG. 6 shows a schematic cross-sectional view in the production apparatus for producing the plate-like crystalline silicon of the present invention.

  In FIG. 6, a plate-like crystalline silicon manufacturing apparatus includes a plate-like silicon 61 on which crystal has been grown, a substrate 62 for growing plate-like silicon, a crucible 63, a silicon melt 64, a heater 65, and a crucible base 66. , A heat insulating material 67, a crucible lifting / lowering base 68, and a shaft 69 fixed to the substrate. However, in FIG. 6, the means for moving the substrate 61, the means for raising and lowering the crucible table 66, the means for controlling the heater, the means for additionally introducing silicon, and the outside of the apparatus such as a chamber capable of evacuation are shown. Not listed.

  In FIG. 6, the crystal-grown plate-like silicon 61, the substrate 62 for growing the plate-like silicon, the crucible 63, the silicon melt 64, the heater 65, the crucible base 66, the heat insulating material 67, and the crucible lifting base 68 The shaft 69 fixed to the substrate is installed in a chamber with good airtightness, and it is necessary to have a structure capable of performing gas replacement with an inert gas 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, and it is more cost-effective to construct a circulation system. Connected. Further, when a gas containing an oxygen component is used, silicon oxide is generated and adheres to the substrate surface and the chamber wall. Therefore, it is necessary to remove the oxygen component as much as possible. Further, it is preferable to remove silicon oxide particles through a filter or the like in the gas circulation system.

  Here, the structure of the plate-like crystalline silicon shown in FIG. 6 will be described. In FIG. 6, the substrate 62 having a temperature equal to or lower than the silicon melt temperature enters the silicon melt 64 in the crucible 63 from the left side in the figure and is immersed in the silicon melt 64. At this time, the silicon melt is held by the heater 65 above the melting point. It is preferable from the viewpoint of reproducibility of the production of the plate-like silicon that the melt temperature is adjusted, the atmospheric temperature in the chamber, and the temperature of the substrate 62 can be strictly controlled. The material of the substrate is not particularly limited, but is preferably a material having good thermal conductivity or a material having excellent heat resistance, and more preferably graphite subjected to high purity treatment or the like. For example, high-purity graphite, silicon carbide, quartz, boron nitride, alumina, zirconium oxide, aluminum nitride, metal, or the like can be used, but an optimal material may be selected according to the purpose. High-purity graphite is more preferable because it is a relatively inexpensive material that is rich in workability. The material of the substrate is industrially inexpensive, and the combination of the melt material and the substrate can be appropriately selected in consideration of various characteristics such as the quality of the obtained silicon plate. Further, when a metal is used for the substrate, there is no particular problem as long as the metal is used at a temperature not higher than the melting point of the substrate and does not significantly affect the characteristics of the obtained silicon plate.

  To facilitate temperature control, it is convenient to use a copper substrate. Substrate cooling means can be broadly divided into three types: natural cooling, direct cooling, and indirect cooling. Natural cooling means that a high-temperature substrate and plate-like silicon release radiant heat immediately after immersion and lower the temperature without using a special cooling means. There is an advantage that the device configuration is simplified. Direct cooling is a means for cooling by blowing gas directly onto the substrate. Indirect cooling is a means for indirectly cooling the substrate with 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, or helium for the purpose of preventing oxidation of the plate-like silicon. In particular, considering cooling capacity, helium or a mixed gas of helium and nitrogen is preferable, but nitrogen is preferable in consideration of cost. The cooling gas can be circulated using a heat exchanger or the like to further reduce the cost, and as a result, inexpensive plate-like silicon can be provided.

  Furthermore, a mechanism capable of heating the substrate can be provided. The heating mechanism may be a high frequency induction heating method or a resistance heating method. However, it is better not to affect the heater for heating to maintain the molten state of silicon. As described above, by using the cooling mechanism and the heating mechanism in combination, the stability of manufacturing the plate-like silicon is remarkably improved.

  The temperature of the melt is preferably equal to or higher than the melting point. This can be controlled by a plurality of thermocouples or radiation thermometers. In order to strictly control the melt temperature, it is direct to immerse the thermocouple in the melt, but this is not preferable because impurities from a thermocouple protective tube or the like are mixed into the melt. Further, if the temperature of the melt is set in the vicinity of the melting point, there is a possibility that the molten metal surface of the silicon is solidified due to the protective tube coming into contact with the melt. Therefore, it is preferable to indirectly control the temperature by inserting a thermocouple into a crucible or the like at a position where it does not directly contact the silicon melt.

  The crucible 63 containing the melt is installed on the heat insulating material 67. This is used to keep the melt temperature uniform and to suppress heat removal from the bottom of the crucible. A crucible stand 66 is installed on the heat insulating material 67. The crucible base 66 is connected to a crucible lifting / lowering shaft 68 and needs to be provided with a lifting / lowering mechanism. This is because, in order to grow the silicon plate on the substrate 62, it is preferable that the substrate 62 is always immersed in the melt 64 at the same depth regardless of the increase or decrease of the melt.

  Since the silicon in the crucible decreases with the production of the plate-like crystalline silicon, it is necessary to replenish the crucible with timely silicon. As a method of replenishing the crucible with silicon, it is possible to use a method in which a polycrystalline silicon body (lumps) is melted and charged, sequentially charged as a melt, or powder is sequentially charged. There is no particular limitation. However, it is preferable not to disturb the melt surface as much as possible. This is because if the melt surface of the melt is disturbed, the wave shape generated at that time is reflected on the melt surface side of the plate-like silicon to be obtained, and the uniformity of the obtained sheet may be impaired.

(Plate-like silicon manufacturing method)
Next, a method for producing plate-like crystalline silicon according to the present invention will be described using the plate-like silicon production apparatus shown in FIG.

  First, a high-purity graphite crucible 63 is filled with a silicon raw material whose impurity concentration is adjusted so that the specific resistance of the obtained plate-like silicon becomes a desired value. The crucible is installed in an apparatus as shown in FIG. Next, the inside of the chamber is evacuated to reduce the pressure in the chamber to a predetermined pressure. After that, it is desirable to introduce Ar gas into the chamber and keep Ar gas flowing. The reason why the gas is constantly flowed in this way is to obtain a clean silicon surface.

  Next, the temperature of the silicon melting heater 65 is set to be equal to or higher than the melting point of silicon to completely melt the silicon lump in the crucible 63.

  Thereafter, the silicon melt temperature is set to a desired value and held for 30 minutes to stabilize the melt temperature, and the crucible 63 is moved to a predetermined position using the crucible lifting mechanism 68.

  Next, the base plate for manufacturing the plate-like silicon is advanced from the left side to the right side in FIG. 6 to grow the plate-like silicon. At this time, the crystal growth surface side of the base plate is moved while being in contact with the silicon melt. Thus, plate-like silicon is formed by the crystal growth surface of the base plate being in contact with the silicon melt. In particular, the surface temperature of the substrate when entering the silicon melt is preferably 300 ° C. or higher and 1100 ° C. or lower.

  This is because stable control becomes difficult when the temperature of the substrate is 300 ° C. or lower. That is, in the case of continuous production, the substrate waiting to be immersed in the chamber receives radiant heat from the silicon melt and is difficult to maintain at 300 ° C. at all times, leading to variations in the quality of the obtained silicon plate. Because. Further, if the temperature of the substrate is 1100 ° C. or higher, the growth rate of the plate-like silicon is slowed and productivity is deteriorated, which is not preferable.

  In order to adjust the temperature of the substrate, it is preferable to have both a cooling mechanism and a heating mechanism. By providing these mechanisms, not only productivity can be improved, but also the yield of products can be improved and the quality can be stabilized.

  Here, the plate-like crystalline silicon manufacturing apparatus shown in FIG. 6 is taken as an example, but the apparatus is not particularly limited to this apparatus. Any device capable of growing plate-like silicon by bringing the base plate into contact with the silicon melt may be used.

(Plate-shaped base plate for crystalline silicon production)
Examples of the base plate for producing crystalline silicon in the present invention include those shown in FIGS. 3B, 4B, and 5B. By using these base plates, periodic crystals can be obtained, which is desirable in terms of the uniformity of the obtained plate-like silicon. In addition, the distance between adjacent growth start convex portions is preferably about 0.5 mm or more and 5.0 mm or less. The reason is that, as described above, the conversion efficiency of the solar cell can be obtained to some extent if it is 0.5 mm or more, and unevenness is less likely to be noticed if it is 5.0 mm or less. Of these, a thickness of about 1.0 mm to 3.0 mm is particularly preferable. Here, such a distance between the convex portions can be easily evaluated by visual observation or observation with a microscope.

  The height of the growth starting convex portion may be determined by the balance between the surface tension of the silicon melt and the energy at the interface between the base plate and the silicon melt. The surface tension varies depending on the melt temperature to be set, and the interfacial energy varies depending on the material of the base plate and the distance between the convex portions of the growth starting point (vertical angle of the convex portion) as well as the melt temperature. It is necessary to change together. As a guide, it may be about 0.05 mm or more, more preferably 0.1 mm or more.

  Hereinafter, the present invention will be described based on specific examples.

(Examples 1-3, Comparative Examples 1-3)
<Production of plate-like crystalline silicon>
As described in the above embodiment, plate-like crystal silicon was produced using the plate-like crystal silicon manufacturing apparatus of FIG. Specifically, it is as follows.

  A silicon raw material whose boron concentration was adjusted so as to have a specific resistance of 2.0 Ω · cm was placed in a quartz crucible protected by a high-purity carbon crucible and fixed in the chamber shown in FIG.

  First, the inside of the chamber is evacuated to about 5 Pa and replaced with normal pressure Ar gas. After that, Ar gas is introduced into the chamber and returned to normal pressure. Thereafter, Ar gas is constantly supplied from the top of the chamber at 2 L / min. Leave it flowing. Next, the silicon raw material is melted by a heater. The temperature of the silicon melting heater is increased to 1500 ° C. at a temperature increase rate of 10 ° C./min, and it is confirmed that the silicon raw material is completely dissolved. Keep at ℃ to stabilize.

  Next, the temperature when the base plate having the shape shown in FIGS. 3 (B), 4 (B) and 5 (B) enters the silicon melt is set to 500 ° C., and the position is 8 mm from the surface of the silicon melt. So as to pass through the substrate, and crystallize the plate-like silicon on the surface of the base plate. The base plate used was a high purity treated graphite base plate having outer dimensions of 130 mm in length, 130 mm in width, and 30 mm in thickness. Further, the distance between adjacent growth start convex portions was about 2.5 mm, and the height of the growth start convex portion was 0.3 mm.

  The plate-like silicon thus obtained had shapes as shown in FIGS. 3 (A), 4 (A) and 5 (A), respectively.

  In each of the obtained plate-like crystalline silicon, a solar cell was manufactured with the surface side that was in contact with the base plate as the light incident surface, and Example 1 and Example 2 corresponded to each plate-like crystalline silicon. And Example 3. In addition, in the obtained plate-like crystalline silicon, a solar cell was manufactured with the surface facing the surface that was in contact with the base plate at the time of manufacture as a light incident surface, and each plate-like crystalline silicon was adapted to each plate-like crystalline silicon. Comparative Example 1, Comparative Example 2 and Comparative Example 3 were obtained.

<Production of solar cells and evaluation of cell characteristics>
The plate-like crystalline silicon obtained as described above was cut with a laser to obtain plate-like silicon having a length of 125 mm × width of 125 mm.

  First, in the plate-like crystalline silicon, alkali etching was performed using sodium hydroxide to form irregularities on the light incident surface. The etching was performed by heating several percent sodium hydroxide to about 90 ° C. and immersing the silicon substrate in the sodium hydroxide.

Thereafter, an n + layer was formed by POCl ₃ diffusion. Next, after removing excess PSG (phospho-silicate glass) film formed on the surface with hydrofluoric acid, a plasma CVD apparatus is used on the n + layer on the light-receiving surface side of the solar cell. A silicon nitride film was formed.

  Next, the n + layer formed also on the surface which becomes the back surface side of the solar cell was removed by etching with a mixed solution of nitric acid and hydrofluoric acid to expose the p-type part. Next, a back electrode mainly composed of an aluminum paste was formed thereon by screen printing, followed by firing to form a p + layer at the same time.

  Next, an electrode containing silver as a main component was formed on the light-receiving surface side by a screen printing method, and baked. Thereafter, solder dipping was performed on the silver electrode portion to produce a solar cell.

The obtained solar cell was evaluated for cell characteristics according to “Crystalline Solar Cell Output Measurement Method (JIS C 8913 (1988))” under irradiation of AM 1.5 and 100 mW / cm ² .

  Moreover, the average dimension and average crystal grain size of the surface shape of the light incident surface of the solar cell on which the cell characteristics were evaluated were evaluated. The average size of the surface shape of the light incident surface is obtained by taking a photograph of the light incident surface of the solar cell and calculating the number of pattern boundaries (n) that a line segment of known length (L) crosses by 10 line segments. And the average value of L / n was calculated. The photograph was taken at a magnification of 25 using a digital microscope VH-7000 manufactured by Keyence Corporation.

  The average crystal grain size is calculated by polishing the light incident surface of the solar cell obtained as described above with abrasive grains having a roughness of about 10 microns and then smoothing it, and then adding nitric acid (nitric acid 3 : The crystal grain boundary is selectively etched by lightly etching with hydrofluoric acid 1), and then the number of grain boundaries crossed by a line segment of a known length (L) in the same manner as described above ( B) was counted for 10 line segments, and the average crystal grain size was calculated by the average value of L / b.

  Table 1 also shows the results of the sensory test regarding the average size of the surface shape of the light incident surface of the crystalline silicon, the average crystal grain size, the conversion efficiency of the solar cell, and the unevenness of the solar cell. In the sensory test, 50 monitors with a visual acuity of approximately 1.0 or more observe the appearance of the solar cell from a position 2 meters away. ), Neither (3 points), little concern (4 points), no concern at all (5 points), and the average score was calculated.

  As is clear from Table 1, the average size of the surface shape of the light incident surface is more when the surface side of the plate-like crystalline silicon that is in contact with the base plate at the time of manufacture is the light incident surface. It turned out to be smaller and less noticeable. This is presumably because the surface on the base plate side in crystalline silicon grows in a supercooled state, so that roughening does not easily occur and a surface with an orientation close to the facet surface is likely to appear. Therefore, even one crystal grain is surrounded by a plurality of surfaces close to different facet surfaces, and it is considered that when anisotropic etching is performed with an alkaline aqueous solution, it is divided into a plurality of patterns.

  In addition, although the case where the solar cell was produced by using the surface on the side opposite to the surface side that was in contact with the base plate at the time of manufacturing in the plate-like crystalline silicon as the light incident surface was referred to as Comparative Examples 1 to 3. Similar results were obtained when the surface of the crystalline silicon in contact with the base plate during production was polished and smoothed, and then the solar cell was produced using the smooth surface as the light incident surface.

(Comparative Example 4)
Except for producing a solar cell using a substrate obtained by a casting method having a surface shape with an average size on the light incident surface of the plate-like crystalline silicon used in Example 1 and having substantially the same crystal grain size These were all made in the same manner as in Example 1 and set as Comparative Example 4.

  Using the cast substrate, a solar cell was manufactured by the above-described solar cell manufacturing method, and the characteristics evaluation of the solar cell and the unevenness evaluation by the sensory test were performed by the same method. The results are shown in Table 1.

  From the results in Table 1, it was found that the solar cell of the present invention can achieve both ensuring of crystal grain size and non-uniformity.

Example 4
Plate-like silicon was produced under the same conditions except for the plate-like silicon used in Example 1 and the depth when the base plate was immersed. By changing the base plate immersion depth at that time from 4 mm to 12 mm, the balance between the buoyancy and the surface tension in the melt is changed, and the difference between the concave and convex shapes on the surface on the base plate side is 5 μm to 290 μm. Produced.

  In the obtained plate-like crystalline silicon, a solar cell was produced by the process described in Example 1 using the surface side that was in contact with the base plate during production as the light incident surface, and the average crystal grain size and the light incident surface were obtained. The ratio of the average size of the surface shape and the conversion efficiency of the solar cell were evaluated. The results are shown in Table 2. In the plate-like crystalline silicon, when the difference in the uneven shape of the light incident side surface is 20 or more, the ratio of the average crystal grain size to the average size of the surface shape of the light incident surface suddenly increases, resulting in unevenness. It turns out that it is effective for suppression. When the thickness is less than 200 μm, printing of the silver paste on the incident surface side is good, and the conversion efficiency shows almost no shape dependence, but when it is larger than 200 μm, the printing defect increases rapidly, and the conversion efficiency decreases. It was. From this result, it can be seen that the difference in the uneven shape of the light incident side surface of the plate-like crystalline silicon is desirably about 20 to 200 μm.

(Example 5)
A plate-like crystalline silicon having the shape shown in FIG. 3 (B) having a period of 0.2, 0.5, 1, 2.5, 4, 5, and 7 mm is manufactured, and the base plate is manufactured. The solar cell was manufactured by the above-mentioned process using the surface side in contact with the light incident surface. The above-mentioned sensory test was conducted together with the conversion efficiency evaluation of the solar cell as an evaluation item of the produced solar cell. The results are shown in Table 3.

  The conversion efficiency is drastically improved when the period is 0.5 mm or more. It can also be seen that the average point of the sensory test goes up when the period is 5 mm or less. From this result, it can be seen that the period is preferably about 0.5 mm or more and 5 mm or less.

  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.

It is a schematic perspective view which shows the solar cell of this invention. It is a schematic perspective view which shows the solar cell produced from the general cast board | substrate. (A) is a schematic perspective view of plate-shaped silicon, (B) is a schematic perspective view of the base plate used when manufacturing the plate-shaped silicon of (A). (A) is a schematic perspective view of plate-shaped silicon, (B) is a schematic perspective view of the base plate used when manufacturing the plate-shaped silicon of (A). (A) is a schematic perspective view of plate-shaped silicon, (B) is a schematic perspective view of the base plate used when manufacturing the plate-shaped silicon of (A). It is a schematic sectional drawing of the manufacturing apparatus of plate-shaped crystalline silicon.

Explanation of symbols

  K1, K2 polycrystalline silicon, C3, C4 base plate, S3, S4 plate silicon, B crystal grain boundary, G11, G12, G13, G21, G22, G23 crystal grain, P131, P132, P133, P134, P135, P136 Surface shape area.

Claims (8)

In the solar cell using a crystalline silicon, single crystal grains of the surface at the light incident surface of the crystalline silicon, characterized Rukoto to have a region where the uneven pattern differs 2 or more, the solar cell. Said one of surfaces of crystal grains is one-time anisotropic etching, the uneven pattern characterized that you form two or more different regions, solar cell according to claim 1.   3. The solar cell according to claim 1, wherein a light incident surface of the crystalline silicon is constituted by a (111) plane of the crystalline silicon.   The solar cell according to any one of claims 1 to 3, wherein a difference in the uneven shape of the light incident surface is 20 µm or more and 200 µm or less.   The solar cell according to any one of claims 1 to 4, wherein the crystalline silicon is produced by bringing a base plate into contact with a silicon melt and growing crystals on the base plate.   The solar cell according to claim 5, wherein the light incident surface is a surface of the crystalline silicon that is in contact with a base plate.   The solar cell according to claim 1, wherein the surface shape is substantially periodic.   The solar cell according to claim 7, wherein the range of the period of the surface shape is 0.5 mm or more and 5.0 mm or less.

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