JP2006066732A - Manufacturing method of granular crystal, photoelectric converter, and photovoltaic generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high quality granular crystals by arranging a large number of grains consisting of crystal material on a base board, introducing it into a heating furnace, heating and melting the grains, and thereafter hardening the melted grains. <P>SOLUTION: By arranging a large number of the grains consisting of the crystal material respectively in recesses 3 at the base board 2 where a large number of recesses for holding the grains 1 respectively are formed on its upper surface, introducing it into the heating furnace 10, heating and melting the grains 1, and thereafter hardening the melted grains 1 to be the granular crystal 1; contact of the granular crystals 1 with each other is avoided to effectively suppress combining of the granular crystals 1 with each other due to contact, and to exclude the start point of hardening from a contact. Thus, the start point of hardening in the case of hardening can be only a contact with the base board 2, so that the granular crystals 1 are obtained having crystallinity of a granular shape and a high quality where sub grain does not occur. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing granular crystals, and in particular, a conversion method using granular silicon crystals produced by using the production method of granular crystals suitable for obtaining granular silicon crystals for use in photoelectric conversion devices, and the production method thereof. The present invention relates to a photoelectric conversion device and a photovoltaic device having excellent characteristics.

  Photoelectric conversion devices are being developed in response to market needs such as high efficiency in terms of performance, consideration of resource finiteness, and low manufacturing costs. As one of promising photoelectric conversion devices in the future market, solar cells using granular silicon crystals as constituent elements of photoelectric conversion means are attracting attention. As a method for producing this granular silicon crystal, a technique is known in which a silicon raw material is melted in a container using infrared rays or high frequency, and this molten material is freely dropped as droplets to obtain a granular silicon crystal.

  The granular silicon crystal manufactured by such a method is like single crystal silicon grown by CZ (Czochralski) method or polycrystalline silicon produced by casting method using an expensive semiconductor grade silicon material. Because there is no need to grind to make a thin substrate of about 300 μm after columnar crystals are produced, expensive silicon materials are not wasted in the dicing process and grinding process, and the use efficiency of silicon materials is excellent There is a feature that.

As raw materials for producing granular silicon crystals, for example, fine silicon particles generated as a result of pulverizing polycrystalline silicon, high-purity silicon vapor-phase synthesized by a fluidized bed method, or the like is used. In order to produce granular silicon crystals from these raw materials, the raw materials are separated according to size or weight, then melted in a container using infrared rays or high frequency, and this melt can be freely used as droplets (granular melt). There is a method of dropping (see, for example, Patent Document 1, Patent Document 2, and Patent Document 4). In addition, there is a method (see Patent Document 3) in which molten silicon is scattered to form a particulate crystal.
International Publication No. 99/22048 U.S. Pat.No. 4,188,177 JP-A-5-78115 US Pat. No. 6,432,330 U.S. Pat.No. 4,430,150

  However, most of the granular silicon crystals produced by these methods are polycrystalline because the droplets are rapidly cooled, so that the solidification rate becomes extremely fast and it is difficult to grow into a single crystal. Since a polycrystalline body is an aggregate of small crystals, a grain boundary exists between the small crystals. In this grain boundary, the recombination centers of carriers are gathered at the boundary of the grain boundary, and the recombination causes the lifetime of minority carriers to be greatly reduced. Therefore, in the semiconductor device using a polycrystalline body, This causes a problem of deteriorating electrical characteristics.

  In the case of a semiconductor device such as a photoelectric conversion device in which electrical characteristics are greatly improved with an increase in the lifetime of minority carriers, the presence of grain boundaries in the granular silicon crystal used in the semiconductor device deteriorates the electrical characteristics. , Especially a big problem. In other words, if the granular silicon crystal can be changed from a polycrystal to a single crystal, the electrical characteristics of the photoelectric conversion device can be remarkably improved.

  In addition, since the grain boundaries in the polycrystalline body lower the mechanical strength of the granular silicon crystal composed of the polycrystalline body, the thermal history and thermal distortion of each process for manufacturing the photoelectric conversion device, or mechanical pressure, etc. There was also a problem that granular silicon crystals were easily destroyed.

  Therefore, when manufacturing a photoelectric conversion device using granular silicon crystals, it is necessary to manufacture granular silicon crystals made of a polycrystalline or single crystal having excellent crystallinity and having no grain boundaries inside. It becomes.

  As a method for obtaining such polycrystalline silicon or single crystalline crystalline silicon, a silicon compound film such as a silicon oxide film is formed on the surface of granular polycrystalline silicon or amorphous silicon. Then, a method for producing a granular silicon crystal composed of a polycrystal or a single crystal excellent in crystallinity by melting and solidifying the silicon inside the silicon compound film after cooling is known (for example, (See Patent Document 5).

  However, in order to form a photoelectric conversion device with excellent electrical characteristics, a large number of high-quality granular silicon crystals are required, whereas in conventional granular silicon crystals, adjacent granular silicon crystals are combined, Since the solidification starting point is both a contact point with the base plate side and a contact point with the adjacent granular silicon crystal, and becomes polycrystalline, there is a problem that it is difficult to obtain a desired high quality granular silicon crystal.

  The present invention has been made in view of the above problems in the prior art, and has been made to solve these problems. The object of the present invention is to provide a granular silicon crystal having high crystallinity and at the same time, stably crystallizing with high efficiency. It is in providing the manufacturing method of the granular crystal which can obtain.

  Another object of the present invention is to provide a photoelectric conversion device and a photovoltaic device excellent in electrical characteristics using the granular crystal having high crystallinity obtained by the method for producing granular crystal of the present invention. It is in.

  The method for producing granular crystals according to the present invention includes 1) a heating furnace in which a large number of particles made of a crystal material are arranged in the recesses of a base plate provided with a plurality of recesses for holding the particles on the upper surface, respectively. After being introduced into the inside and heating and melting the particles, the melted particles are solidified to form granular crystals.

  In addition, in the method for producing a granular crystal of the present invention, 2) in the configuration of 1), the recess has an opening smaller than the diameter of the particle and a depth shallower than the radius of the particle. Is.

  In addition, the method for producing a granular crystal of the present invention is characterized in that 3) in the configuration of 1), the concave portion is disposed so as to be positioned at each lattice point of a simple hexagonal lattice.

  In the photoelectric conversion device of the present invention, 4) a large number of granular silicon crystals of the first conductivity type are formed on one main surface of a conductive substrate, and the lower part is bonded to the conductive substrate, and insulation is provided between adjacent ones. A photoelectric conversion device in which a substance is interposed and an upper portion is exposed from the insulating substance, and a semiconductor layer of a second conductivity type and a translucent conductor layer are sequentially provided on the granular silicon crystal, The granular silicon crystal is produced by the method for producing a granular crystal according to any one of 1) to 3) above.

  The photovoltaic power generation apparatus of the present invention is configured such that 5) the photoelectric conversion device having the configuration of 4) above is used as power generation means, and the generated power of this power generation means is supplied to a load.

  According to the method for producing a granular crystal of the present invention, a large number of particles made of a crystal material are arranged in the recesses of the base plate provided with a plurality of recesses for holding the particles on the upper surface, respectively, in the heating furnace. After introducing and heating and melting the particles, the molten particles are solidified to form granular crystals, so that the particles that become granular crystals can be prevented from contacting each other during melting. Therefore, it is possible to effectively produce a granular crystal having a spherical shape with no generation of subgrains. In addition, since the starting point of crystal growth from the contact portion of the particles can be excluded when the particles are solidified to form a granular crystal, the crystallinity in the granular crystal can be determined by setting the solidification starting point when solidifying only the recess of the base plate. Can be improved.

  Further, according to the method for producing granular crystals of the present invention, when the recess has an opening smaller than the diameter of the particle and the depth is shallower than the radius of the particle, the particles made of the crystalline material before melting are arranged in the recess. Sometimes more than half of the volume of the particles comes out on the base plate. As a result, when the particles are solidified after melting, the solidification starting point becomes the contact point between the concave portion of the base plate located in the lower half of the particle and the particle, and the crystal growth in a large number of granular crystals is stable. become.

  Further, according to the method for producing granular crystals of the present invention, when the concave portions are arranged so as to be positioned at the respective lattice points of the simple hexagonal lattice, the particles are placed in a high density state close to the close-packed arrangement on the base plate. The number of particles that can be arranged and processed in the same process can be increased, and as a result, the amount of atmospheric gas used per granular crystal can be reduced, and the heating cost can be reduced. it can.

  According to the photoelectric conversion device of the present invention, a large number of granular silicon crystals of the first conductivity type are bonded to one main surface of a conductive substrate and the lower portion is bonded to the conductive substrate, and an insulating material is provided between adjacent ones. And a photoelectric conversion device in which a second conductive type semiconductor layer and a translucent conductor layer are sequentially provided on the granular silicon crystal, the granular silicon crystal being disposed with the upper portion exposed from an insulating material. Is produced by the above-described method for producing granular crystals of the present invention, so that a large number of granular silicon crystals can be mass-produced as high-quality crystalline silicon particles by the method for producing granular crystals of the present invention. Since it can be manufactured, the silicon material used in the photoelectric conversion device can be used efficiently, and at the same time, the high-quality granular silicon crystal makes the photoelectric conversion device highly efficient and reliable. It can be improved.

  According to the photovoltaic power generation apparatus of the present invention, the photoelectric conversion apparatus of the present invention is used as a power generation means, and the generated power of this power generation means is supplied to the load, so that it is highly efficient and reliable. The power generation capability is improved by the high photoelectric conversion device of the present invention, and reliability can be secured stably over a long period of time.

  As described above, according to the method for producing granular crystals of the present invention, a large number of granular crystals can be stably and efficiently crystallized, and at the same time, granular crystals having high crystallinity can be easily mass-produced. Therefore, by using this, it is possible to provide a good photoelectric conversion device excellent in photoelectric conversion characteristics and a photovoltaic device using the photoelectric conversion device.

  Hereinafter, the manufacturing method of the granular crystal of this invention is demonstrated in detail, referring an accompanying drawing.

  FIG. 1 is a perspective view showing a base plate in an example of an embodiment of the method for producing granular crystals of the present invention, and FIG. 2 is an enlarged sectional view thereof. FIG. 3 is a side view showing a schematic configuration in an example of an embodiment of the method for producing granular crystals of the present invention. 1 to 3, 1 is a particle or granular crystal made of a crystal material, 2 is a base plate, and 3 is a plurality of concave portions provided on the upper surface of the base plate 2. Further, 10 is a heating furnace, 11 is a base plate 2 introduced into the heating furnace 10 together with the particles 1 placed on the upper surface, and the base plate 2 on which the granular crystals 1 are placed is discharged from the heating furnace 10. This is a transport mechanism.

  In this embodiment, an example in which silicon is used as a crystal material will be described.

  First, semiconductor grade crystalline silicon is used as the crystal material, and this is melted in a container using infrared rays or a high-frequency coil, and then the polycrystalline silicon is melted and dropped by a free fall as a granular melt. Silicon particles 1 are obtained.

The polycrystalline silicon particles 1 produced by the melt drop method are usually doped with a dopant in order to obtain a desired conductivity type and resistance value. As dopants for silicon, boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony are used. However, boron or phosphorus is used because it has a large segregation coefficient for silicon and a small evaporation coefficient when silicon is melted. desirable. The dopant concentration is about 1 × 10 ¹⁴ to 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.

  At the time when the silicon particles 1 are obtained by this melting and dropping method, the shape of the silicon particles 1 is a teardrop type, a streamline type, or a connected type in which a plurality of particles are connected in addition to a substantially spherical shape. . When a photoelectric conversion device is produced using the polycrystalline silicon particles 1 as it is, good photoelectric conversion characteristics cannot be obtained. This is due to metal impurities such as Fe, Cr, Ni, and Mo that are normally contained in the polycrystalline silicon particles 1 and due to the carrier recombination effect at the polycrystalline grain boundaries. In order to improve this, the polycrystalline silicon particles 1 are remelted in a temperature-controlled heating furnace by the method for producing granular crystals of the present invention, and then cooled and solidified, for example, in an oxygen / nitrogen atmosphere. A single crystal granular silicon crystal 1 having a low impurity content is used.

  In order to produce the single crystal granular silicon crystal 1, first, a large number of polycrystalline silicon particles 1 are placed side by side on the upper surface of the plate-like base plate 2. As the material of the base plate 2, quartz glass, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for suppressing the reaction with the silicon particles 1, but from the viewpoint of low cost and easy handling. Glass is preferred.

  Next, the polycrystalline silicon particles 1 placed on the upper surface of the base plate 2 are introduced into the heating furnace 10 and heated. As the heating furnace 10, various types can be used depending on the type of crystal material. However, when silicon is used as the crystal material, it is generally used in an atmosphere firing furnace used for firing ceramics or the process of manufacturing semiconductor elements. A horizontal oxidation furnace or the like that is commonly used is suitable, and an induction heating or resistance heating heater is desirable as a heating source.

  Before heating in the heating furnace 10, the inside of the heating furnace 10 is subjected to vacuum treatment or gas replacement in an inert gas atmosphere in order to prevent the contamination of organic substances on the surface of the silicon particles 1. It is desirable that Argon, nitrogen, helium, and hydrogen are suitable as the inert gas, but argon or nitrogen is preferred from the viewpoint of low cost and easy handling.

  Next, the entire silicon particle 1 is heated in the heating furnace 10 by induction heating or a resistance heater. The temperature in the heating furnace 10 is maintained at a temperature higher than the melting point of silicon while introducing a reactive gas composed of oxygen gas and nitrogen gas. At this time, in the process of being introduced into the heating furnace 10 and being heated, silicon reacts with the atmosphere to form a silicon compound film on the surface of the silicon particles 1.

  Here, in the heating in the conventional method for producing a granular crystal, the polycrystalline silicon particles 1 are randomly arranged on a base plate having a flat upper surface, and therefore there are many places where the silicon particles 1 are in contact with each other. In other words, in the process in which the silicon particles 1 in contact with each other are melted, the silicon particles 1 are welded to each other, and an union of silicon particles 1 such as an array type may be formed. In addition, when silicon particles melted on the base plate solidify, the contact point with the base plate becomes a solidification starting point, and solidification proceeds from the solidification starting point to the other pole of the particle, so that crystallization progresses sequentially. However, in the conventional case, the point of contact with other silicon particles that are in contact with each other also becomes a solidification starting point, and therefore, multiple crystallizations proceed in the particles, resulting in crystallinity. There was something that wasn't good.

  On the other hand, in the method for producing granular crystals of the present invention, as shown in FIGS. 1 and 2, a plurality of recesses 3 for holding the particles 1 are provided on the upper surface of the base plate 2 made of quartz or the like, A large number of particles 1 made of a crystalline material are arranged in the recess 3 of the base plate 2. Then, as shown in FIG. 3, the base plate 2 is introduced into the heating furnace 10 using the transport mechanism 11, the particles 1 are heated and melted, and then the melted particles 1 are solidified to form granular crystals. 1 makes it possible to reliably avoid contact between the particles 1 arranged on the upper surface of the base plate 2, and to effectively suppress coalescence of the particles 1 due to contact. It is possible to produce a high-quality granular crystal 1 having a spherical shape without any defects. Moreover, since the solidification starting point from the contact part of particle | grains 1 can be excluded when the melted particle | grains 1 solidify, it is granular by making only the contact part (concave part 3) with the baseplate 2 the solidification starting point at the time of solidification. The crystallinity of the crystal 1 can be improved.

  The recess 3 may have a circular shape as illustrated in the figure, but is not limited to a circular shape, and may be a quadrangle, a triangle, an ellipse, or the like. Further, the cross-sectional shape of the recess 3 is not limited to the circular shape as shown in FIG. 2, and may be a quadrangular shape, a triangular shape, an elliptical shape, or the like. The shape of the recess 3 is such that a smaller number of contact points between the particles (granular crystals) 1 and the base plate 2 can suppress the increase and dispersion of solidification starting points during solidification, and can improve the crystallinity of the obtained granular crystals 1. Should be determined in consideration of

  Further, the recess 3 preferably has an opening smaller than the diameter of the particle 1 and a depth shallower than the radius of the particle 1. By setting the size of the recesses 3 in this way, when the particles 1 before melting are arranged in the recesses 3, more than half of the volume of the particles 1 comes out on the base plate 2. When 1 solidifies after melting, the solidification starting point becomes the contact point between the concave portion 3 located in the lower part of the lower half of the particle 1 and the particle 1 and can always be crystallized from the lower solidification starting point. The crystal growth becomes stable, and it becomes possible to stably obtain a granular crystal 1 having good crystallinity.

  In addition, as shown in a schematic top view in FIG. 4, the recesses 3 are preferably arranged on the top surface of the base plate 2 so as to be positioned at each lattice point of the simple hexagonal lattice in a top view. By arranging the recesses 3 in this way, the particles 1 held on the upper surface of the base plate 2 can be arranged at a high density close to the close-packed arrangement while not contacting each other. Further, since the amount of atmospheric gas and heating resources used per particle 1 can be reduced by increasing the density, resource saving and cost reduction can be achieved. The distance between the lattice points of the simple hexagonal lattice needs to ensure a distance slightly larger than the diameter of the particles 1 held in the recesses 3 arranged so as to be located at the lattice points. If the distance between each lattice point is smaller than the diameter of the particle 1, the adjacent particles 1 are not in contact with each other, and if too large, the particle 1 that can be held on the upper surface of the base plate 2 by the recess 3 is not preferable. This is not preferable because the number is reduced.

  Since the size of the particles 1 including the silicon particles 1 is usually almost spherical, the particle size is desirably 1500 μm or less, and the shape is desirably close to a sphere. However, the shape of the particles 1 is not limited to a spherical shape, and may be a cubic shape, a rectangular parallelepiped shape, or other irregular shapes. When the size of the particle 1 exceeds 1500 μm, a predetermined silicon compound film formed on the surface of the silicon particle 1 becomes relatively thin, so that the shape of the particle 1 when the inner silicon melts. It is difficult to keep the silicon in a stable state, and it becomes difficult to completely melt the silicon inside, and if the melting is incomplete, subgrains are likely to occur, which is not desirable. On the other hand, when the size of the particles 1 is as small as less than 30 μm, it is difficult to maintain the shape of the silicon particles 1 when the silicon compound film on the surface is thin, so that it is difficult to maintain the shape at the time of melting. It is not desirable because the silicon particles 1 arranged in a manner are easily combined. Accordingly, it is desirable that the size of the particle 1 made of a crystalline material is 30 μm to 1500 μm, thereby suppressing coalescence of the particles 1, maintaining the shape of the particle 1 stably, and generating no subgrains. A spherical and high-quality granular crystal 1 can be stably produced.

  As the silicon compound film formed on the surface of the silicon particle 1, a silicon oxide film or an oxynitride film is suitable. However, the density of the film is high and the strength per unit film thickness is high. From the viewpoint that the diffusion preventing power to the inside of the silicon particles 1 is large, it is preferable to form a silicon oxynitride film.

  Further, it is desirable that the atmosphere in the heating furnace 10 by the reactive gas when forming the oxynitride film on the surface of the silicon particle 1 has an oxygen partial pressure and a nitrogen partial pressure of 1% or more, respectively. If the oxygen partial pressure or nitrogen partial pressure in the atmospheric gas is less than 1%, the formation of the oxynitride film formed on the surface of the silicon particles 1 that crystallize the inside becomes insufficient, and the silicon compound film is cracked. Tends to occur.

  The particles 1 introduced into the heating furnace 10 are heated to a temperature equal to or higher than the melting point of the crystal material and, if silicon particles 1, equal to or higher than the melting point of silicon (1414 ° C.), preferably 1480 ° C. or lower. During this time, silicon inside the silicon particles 1 is melted. At this time, the silicon compound film (oxynitride film) formed on the surface of the silicon particle 1 can hold the silicon inside the particle 1 and maintain the shape of the particle 1 when the inner silicon melts. It is. However, when the temperature of the particle 1 is difficult to maintain stably, for example, in the case of the silicon particle 1, when the temperature is raised to a temperature exceeding 1480 ° C., It is difficult to keep the shape of 1 stable, and coalescence with adjacent particles 1 is likely to occur, and a fusion reaction with the base plate 2 is likely to occur, which is not desirable.

  In the case of silicon particles 1, the thickness of the silicon compound film formed on the surface is preferably 1 μm or more in the above-mentioned range of particle sizes. When the thickness is as thin as less than 1 μm, it is not desirable because the coating on the surface is easily broken when the silicon inside melts. In addition, if the silicon compound film has a required strength with a thickness of 1 μm or more, the silicon inside tends to spheroidize with surface tension when melted, whereas the silicon compound film is sufficient in the above temperature range. Therefore, the granular silicon crystal 1 obtained by crystallizing the inside can be made into a shape close to a true sphere. On the other hand, when the thickness of the silicon compound film exceeds 50 μm, the silicon compound film is not easily deformed in the above temperature range, and the shape of the obtained granular silicon crystal 1 is difficult to be a nearly spherical shape. Absent. Therefore, in the case of the silicon particles 1, the thickness of the silicon compound film on the surface is preferably 1 μm to 50 μm with respect to the above range of particle diameter (30 μm to 1500 μm), and thereby, a good shape close to a true sphere is obtained. A granular silicon crystal 1 having a shape can be obtained stably, and a photoelectric conversion device having excellent conversion efficiency can be obtained by using the granular silicon crystal 1 for a photoelectric conversion element.

  Next, the molten particles 1 are cooled to a temperature of about 1400 ° C. or lower in order to solidify the molten silicon in the silicon particles 1, and solidified to form granular silicon crystals (granular crystals) 1. At that time, it is desirable to perform thermal annealing on the granular crystal 1 in the middle, for example, in the case of the granular silicon crystal 1, thermal annealing for 60 minutes or more at a constant temperature of 1000 ° C. or higher. By performing this thermal annealing treatment, it is possible to remove the distortion or the like in the crystal of the granular crystal 1 generated at the time of solidification and to obtain a granular crystal 1 with good crystallinity.

  The granular crystal 1 thus obtained may be subjected to a surface treatment or the like as necessary. For example, for the granular silicon crystal 1, in order to obtain a high-purity granular silicon crystal 1 with good crystallinity, a silicon compound film of 1 μm or more formed on the surface may be removed by etching with hydrofluoric acid. Further, here, in order to remove the crystal surface strained layer having a high impurity concentration on the crystal surface of the granular silicon crystal 1, it is desirable to perform an etching process on the surface of the granular silicon crystal 1 with a thickness of 1 μm or more with hydrofluoric acid. .

  In addition to this, it is also effective to form fine irregularities on the surface of the granular silicon crystal 1. As the method, there are gas etching or alkaline liquid etching such as sodium hydroxide or potassium hydroxide. Such surface irregularities function so as to improve the utilization efficiency of incident light by irregular reflection of light due to irregularities on the surface when the photoelectric conversion device is configured using the granular silicon crystal 1 as a photoelectric conversion element. It becomes. Even if the surface irregularities are too large or too small, a sufficient effect cannot be expected, and by making the surface irregularities such that the arithmetic average roughness Ra is 0.01 μm or more and 5 μm or less, photoelectric conversion is achieved. The utilization efficiency of incident light can be satisfactorily improved by irregular reflection of light in the apparatus.

  According to the method for producing granular crystals of the present invention, it is possible to stably produce a granular crystal 1 having good crystallinity as described above.

  Next, a cross-sectional view of an example of an embodiment of the photoelectric conversion device of the present invention is shown in FIG. As shown in FIG. 5, the photoelectric conversion device of the present invention has a number of first conductivity type, for example, p-type granular silicon crystals 1 on one main surface of the conductive substrate 4, in this example, the upper surface, and a lower portion thereof. For example, it is bonded to the conductive substrate 4 by the bonding layer 5, the insulating material 6 is interposed between adjacent ones of the granular silicon crystals 1, and the upper portions of the granular silicon crystals 1 are exposed from the insulating material 6. The granular silicon crystal 1 has a structure in which a second conductive type, for example, an n-type semiconductor layer 7 and a translucent conductor layer 8 are sequentially provided. In addition, when using this photoelectric conversion apparatus as a solar cell, the electrode 9 is deposited and formed in a predetermined pattern shape on the translucent conductor layer 8, for example, a finger electrode and a bus bar electrode. .

  And in the photoelectric conversion apparatus of this invention, in such a structure, the granular silicon crystal 1 is manufactured by the manufacturing method of the above-mentioned granular crystal of this invention, It is characterized by the above-mentioned. .

  According to the photoelectric conversion device of the present invention, since the granular silicon crystal 1 is manufactured by the granular crystal manufacturing method of the present invention as described above, the granular silicon crystal 1 does not contain impurities and has good crystallinity. By using a method for producing granular crystals that can stably produce a large number of particles, the granular crystal production method of the present invention enables a large number of granular silicon crystals 1 to be mass-produced as high-quality crystalline silicon particles. Since it can be manufactured, the silicon material used for the photoelectric conversion device can be used efficiently, and at the same time, the high-quality granular silicon crystal 1 can improve the efficiency and reliability of the photoelectric conversion device. As a result, a photoelectric conversion device with excellent conversion efficiency can be provided at low cost.

  In the photoelectric conversion device of the present invention, the granular silicon crystal 1 is doped with a dopant for making the first conductivity type, for example, a p-type dopant so as to have a desired resistance value. The p-type dopant includes boron, aluminum, gallium, and indium. However, it is desirable to use boron from the viewpoint of a large segregation coefficient with respect to silicon and a small evaporation coefficient when silicon is melted. The granular silicon crystal 1 may be doped with an n-type dopant. As the n-type dopant, phosphorus, arsenic or the like is desirable.

  Next, a method for manufacturing the photoelectric conversion device of the present invention will be described.

  First, a dopant having a second conductivity type opposite to the first conductivity type of the granular silicon crystal 1 is diffused on the surface of the granular silicon crystal 1 formed as described above by a thermal diffusion method. A conductive semiconductor layer 7 is formed. Electric power is generated by collecting the minority carriers generated by photoelectric conversion in the granular silicon crystal 1 at this portion of the pn junction. The second conductivity type semiconductor layer 7 may be formed by forming a semiconductor layer such as a second conductivity type amorphous silicon layer on the surface of the granular silicon crystal 1.

  Next, the granular silicon crystal 1 is disposed on the conductive substrate 4 on which at least the aluminum layer or the aluminum alloy layer is formed, and at least the surface is conductive, and then heated entirely in a reducing atmosphere. The granular silicon crystal 1 is bonded to the conductive substrate 4 through the bonding layer 5.

  At this time, by using the conductive substrate 4 as a metal substrate containing at least aluminum on its surface, the granular silicon crystal 1 can be bonded at a low temperature, and a light-weight and low-cost photoelectric conversion device can be provided. Further, by making the surface of the conductive substrate 4 rough, it is possible to randomize the reflection of incident light in the non-light-receiving region that reaches the surface of the conductive substrate 4, and to reflect the incident light obliquely. Incident light can be used effectively by re-reflecting the module surface and further photoelectrically converting it by the photoelectric conversion part of the granular silicon crystal 1.

  In order to form the semiconductor layer 7 of the second conductivity type, it is preferable to form the semiconductor layer 7 on the surface of the granular silicon crystal 1 by a thermal diffusion method having a low process cost prior to the bonding of the granular silicon crystal 1 to the conductive substrate 4. For example, Group V P, As, Sb, Group III B, Al, Ga, etc. are used as the second conductivity type dopant, and the granular silicon crystal 1 is accommodated in a diffusion furnace made of quartz, and the dopant is introduced. While heating, the second conductive type semiconductor layer 7 is formed on the surface of the granular silicon crystal 1.

  Next, after the thin glass layer formed on the surface of the granular silicon crystal 1 is removed, a large number of granular silicon crystals 1 are arranged with high density on one main surface (upper surface) of the conductive substrate 4 of the aluminum base substrate. By heating the resultant to an Al—Si eutectic temperature of 577 ° C. or higher, a bonding layer 5 formed of an Al—Si eutectic portion is formed between the lower part of the granular silicon crystal 1 and the conductive substrate 4. Is done.

  Next, an insulating material 6 such as polyimide resin is coated between adjacent ones of the joined granular silicon crystals 1 so as to expose the upper part of the granular silicon crystals 1 and to uniformly coat the entire surface. In this way, the insulating material 6 is provided at the top of each granular silicon crystal 1 by exposing at least the top of the granular silicon crystal 1 and interposing between the adjacent granular silicon crystals 1. Effective contact with the translucent conductor layer 8 or the amorphous silicon layer formed as the second conductive type semiconductor layer 7 is enabled.

  Here, the surface shape of the insulating material 6 between the adjacent granular silicon crystals 1 is a concave shape in which the granular silicon crystal 1 side is high, thereby covering the insulating material 6 and the top thereof. By the difference in refractive index from the sealing resin of the photoelectric conversion module applied in this manner, it is possible to promote irregular reflection of incident light on the granular silicon crystal 1 in a non-light-receiving region without the granular silicon crystal 1 as a photoelectric conversion material. it can.

  Further, a translucent conductor layer 8 is formed from above the exposed semiconductor layer 7 of the granular silicon crystal 1 so that the photocurrent generated in each granular silicon crystal 1 can be collected. The translucent conductor layer 8 is made of a tin-doped indium oxide film, a tin oxide film, a zinc oxide film, or the like, and has an antireflection effect by setting its thickness to about 850 mm, for example. The translucent conductor layer 8 is usually formed by a sputtering method to obtain a highly reliable film quality suitable for mass production, but it should also be formed by a CVD method, a dipping method, an electrodeposition method, or the like. Can do. The translucent conductor layer 8 is formed as an upper electrode on the second conductive type semiconductor layer 7 and also formed on the insulating material 6, and the photoelectric conversion element formed of individual granular silicon crystals 1 is formed on the second conductive type semiconductor layer 7. It can be electrically connected in parallel.

  Thereafter, for example, silver paste or the like is applied in a comb-like shape on the translucent conductor layer 8 to form electrodes 9 such as grit electrodes or finger electrodes and bus bar electrodes, whereby the photoelectric conversion device of the present invention is obtained. .

  According to the photoelectric conversion device of the present invention as described above, a large number of high-quality crystalline silicon particles 1 can be manufactured with high productivity, and silicon materials used in the photoelectric conversion device can be efficiently used, The high-quality granular silicon crystal 1 can improve the efficiency and reliability of the photoelectric conversion device, and provide a high-efficiency and low-cost photoelectric conversion device.

  In addition to the low cost and high efficiency, the photoelectric conversion device according to the present invention is a single crystal in which the granular silicon crystal 1 is a good single crystal, so that the surface is laminated with a weather resistant film. In this case, the strain energy remaining at the grain boundary that forms the polycrystalline interface in FIG. 1 can avoid a fracture mode in which cracks are formed in the grain boundary in the granular silicon crystal 1, so that a light-weight and high weather resistance photoelectric conversion system can be supplied. In a total system using converters and converters, it is possible to increase the amount of power output with the same installation area, so it is possible to reduce mounts, wiring materials, converter costs, etc. per output watt, as well as on the roof. The effect of being able to obtain a larger amount of power generation in a large installation area .

  Next, a specific example of the method for manufacturing a granular crystal according to the present invention and a photoelectric conversion device using the granular silicon crystal manufactured by the cutting will be described along the manufacturing steps.

  First, a flat plate made of quartz glass having a large number of recesses 3 provided on the upper surface by laser processing or machining was prepared. The shape of the recess 3 was circular when viewed from above, the diameter was 200 μmφ, and the depth was 150 μm. The distance between the recesses 3 was set to 500 μm, and the particles 1 made of silicon having a diameter of 400 μm were arranged so as not to contact each other. This arrangement is positioned at each lattice point of a simple hexagonal lattice so that as many particles 1 as possible can be processed at one time.

Next, p-type granular silicon crystals having a boron concentration of 1 × 10 ¹⁶ atoms / cm ³ and a particle size of about 400 μm are prepared and previously held in the recesses 3 provided on the base plate 2 by an aligner. After arranging them, a large number of them were placed on the base plate 2 by holding them in the recesses 3. At this time, it was confirmed that the particles 1 were not in contact with each other. The base plate 2 is laminated on five layers, a flat quartz plate is placed thereon, and the furnace 10 is introduced into the furnace 10 using an atmosphere firing furnace filled with an argon inert gas atmosphere. The temperature is raised while introducing a reaction gas in which oxygen gas and nitrogen gas are mixed into the furnace 10, heated to 1450 ° C. above the melting point of silicon and held for 5 minutes, and a silicon oxynitride film is formed on the surface of the silicon particles 1. After forming and melting the silicon inside, it was cooled and solidified. Further, after the temperature was lowered to 1300 ° C., a thermal annealing treatment for 200 minutes was performed to remove strain in the granular silicon crystal 1. Then, after thermal annealing, the temperature was lowered to around room temperature, and a granular silicon crystal 1 was produced. As a result, coalescence of the granular silicon crystals 1 was not seen on the upper surface of the base plate 2, and most of them had a shape close to a true sphere.

  On the other hand, as a comparative example, each silicon particle was melted and solidified by a heating furnace by a method in which a flat plate made of quartz glass was used as a base plate and silicon particles were randomly arranged on the upper surface. As a result, in the comparative example, about 10% of coalescence of granular silicon crystals occurred.

  Thereby, in the manufacturing method of the granular crystal of this invention, the effect that the coalescence of the granular crystals which generate | occur | produced with the conventional manufacturing method disappeared reliably was confirmed.

  Next, the photoelectric conversion apparatus was produced using the granular silicon crystal 1 obtained by the manufacturing method of the granular crystal of the present invention as described above.

  First, the oxynitride film formed on the surface of the granular silicon crystal 1 manufactured as described above was removed by etching to a predetermined thickness using hydrofluoric acid and hydrofluoric acid.

This granular silicon crystal 1 is placed on a quartz boat, introduced into a quartz tube controlled at 900 ° C., POCl ₃ gas is bubbled with nitrogen and fed into the quartz tube, and the surface of the granular silicon crystal 1 is reached in 30 minutes. Then, an n-type semiconductor layer 7 having a thickness of about 1 μm was formed, and then the surface oxynitride film was removed with hydrofluoric acid.

  Next, an aluminum substrate having a size of 50 mm × 50 mm × thickness 0.3 mm is used as the conductive substrate 4, and the granular silicon crystal 1 is disposed on the upper surface in a close-packed state, and then the eutectic temperature of aluminum and silicon. Heating was performed in a reducing atmosphere furnace of nitrogen containing 5% hydrogen at 600 ° C. exceeding 577 ° C., and the lower portions of a large number of granular silicon crystals 1 were bonded to the conductive substrate 4. At this time, the bonding layer 5 made of a eutectic of aluminum and silicon was formed at the portion where the granular silicon crystal 1 was in contact with aluminum of the conductive substrate 4 and exhibited strong adhesive strength.

  Further, from above, the upper portions of the granular silicon crystals 1 are exposed to each other, an insulating material 6 made of polyimide resin is applied and dried, and a conductive substrate 4 serving as a lower electrode and a translucent conductor serving as an upper electrode. The layer 8 is electrically insulated and separated.

  On this, the translucent conductor layer 8 as an upper electrode film was formed with a thickness of about 100 nm on the entire surface by sputtering.

  Finally, silver paste was patterned in a grid shape with a dispenser to form an electrode 9 composed of finger electrodes and bus bar electrodes. The silver paste pattern was fired at 500 ° C. in the atmosphere.

  As a result of evaluating the electrical characteristics of the thus obtained photoelectric conversion device of the present invention with an AM1.5 solar simulator, a conversion efficiency exceeding 13% could be obtained with good reproducibility.

  In addition, this invention is not limited to the example of the above embodiment, A various change may be added in the range which does not deviate from the summary of this invention. For example, a frame may be formed around the base plate 2, and in this case, the base plate 2 can be easily overlapped, and when the particles 1 are disposed in the recess 3 of the base plate 2 or a heating furnace It is possible to effectively prevent the particles 1 from falling out of the base plate 2 while moving in 10.

It is a perspective view which shows the baseplate in an example of embodiment of the manufacturing method of the granular crystal of this invention. It is an expanded sectional view of the baseplate in an example of an embodiment of a manufacturing method of granular crystals of the present invention. It is a side view which shows schematic structure in an example of embodiment of the manufacturing method of the granular crystal of this invention. FIG. 3 is a schematic top view showing an example of the arrangement of recesses in the method for producing granular crystals of the present invention. It is sectional drawing which shows an example of embodiment of the photoelectric conversion apparatus of this invention.

Explanation of symbols

1: Particles (silicon particles), granular crystals (granular silicon crystals)
2: Base plate 3: Recessed portion 4: Conductive substrate 5: Bonding layer 6: Insulating material 7: Semiconductor layer of second conductivity type 8: Translucent conductor layer 9: Electrode

Claims (5)

A large number of particles made of a crystalline material are respectively placed in the recesses of the base plate provided with a plurality of recesses for holding the particles on the upper surface, introduced into a heating furnace, and the particles are heated and melted. Then, the molten particles are solidified to form granular crystals. The method for producing a granular crystal according to claim 1, wherein the recess has an opening smaller than a diameter of the particle and a depth shallower than a radius of the particle. 2. The method for producing granular crystals according to claim 1, wherein the concave portions are arranged so as to be positioned at respective lattice points of a simple hexagonal lattice. A large number of granular silicon crystals of the first conductivity type are formed on one main surface of the conductive substrate, the lower part is bonded to the conductive substrate, an insulating material is interposed between adjacent ones, and the upper part is the insulating material And a photoelectric conversion device in which a second conductive type semiconductor layer and a light-transmitting conductor layer are sequentially provided on the granular silicon crystals, wherein the granular silicon crystals are defined in claims 1 to 10. Item 6. A photoelectric conversion device manufactured by the method for manufacturing granular crystals according to any one of Items 3 to 3. A photovoltaic power generation apparatus configured to use the photoelectric conversion apparatus according to claim 4 as a power generation means, and to supply the generated power of the power generation means to a load.

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