JP2007173529A - Method for manufacturing crystal semiconductor particles, photovoltaic conversion device, and photovoltaic generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photovoltaic conversion device and photovoltaic generator which can manufacture high quality crystal silicon particles stably and is excellent in mass productivity and in being low cost. <P>SOLUTION: In the manufacturing process of the crystal semiconductor particles 101; a silicon compound coat is formed on the surface of semiconductor particle 101, and the semiconductor particles 101 are crystallized by dropping the temperature and solidifying after melting by heat. In forming the silicon compound coat, the semiconductor particles 101 are laid on a silicon wafer 104 to form the silicon compound coat. The high quality crystal silicon particles 101 excellent in the property of photovoltaic conversion efficiency can be manufactured when used in the photovoltaic conversion device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention particularly relates to a method for producing crystalline semiconductor particles suitable for use in a photovoltaic device such as a solar cell and a photovoltaic device, a photovoltaic device using crystalline semiconductor particles produced by the production method, and a photovoltaic device. About.

2. Description of the Related Art Conventionally, photoelectric conversion devices have been developed in response to market needs such as high efficiency in performance, consideration of resource finiteness, low manufacturing costs, and the like. As one of promising photoelectric conversion devices in the future market, there is a photoelectric conversion device using semiconductor particles used as a solar cell.
As raw materials for producing semiconductor particles, for example, silicon particles, silicon fine particles generated as a result of pulverizing single crystal silicon, high purity silicon vapor-phase synthesized by a fluidized bed method, or the like is used. In order to produce silicon particles from these raw materials, the raw materials are separated by size or weight, then melted in a container using infrared rays or high frequency, and then free-falled (for example, Patent Document 1 and Patent Document) 2), or a method using high-frequency plasma (for example, see Patent Document 3).

However, most of the silicon particles produced by these methods are polycrystalline. Since a polycrystalline body is an aggregate of minute crystals, there are grain boundaries between these minute crystals. This grain boundary deteriorates the electrical characteristics of a semiconductor device using a polycrystal. The reason is that the carrier recombination centers are gathered at the grain boundaries, and the recombination of carriers thereby causes the lifetime of minority carriers to be greatly reduced.
In the case of a semiconductor device whose electrical characteristics are greatly improved with an increase in the lifetime of minority carriers, such as a photoelectric conversion device, the presence of grain boundaries in the silicon particles used therein deteriorates the electrical characteristics and is particularly large. It becomes a problem. In other words, if the silicon particles can be changed from a polycrystal to a single crystal, the electrical characteristics of a photoelectric conversion device using the silicon particles as a photoelectric conversion element can be remarkably improved.

In addition, since the grain boundaries in the polycrystalline body reduce the mechanical strength of the polycrystalline silicon particles, the silicon particles are affected by the thermal history, thermal strain, mechanical pressure, etc. of each process of manufacturing the photoelectric conversion device. There was also a problem that was easily destroyed.
Therefore, in the case of producing a photoelectric conversion device using silicon particles, it is indispensable to produce crystalline silicon particles made of a polycrystal or a single crystal having excellent crystallinity and having no grain boundaries. .

  As a method of obtaining such crystalline silicon particles composed of a single crystal having excellent crystallinity, a silicon compound film such as a silicon oxide film is formed on the surface of polycrystalline silicon or amorphous silicon, and the silicon compound film A method is known in which the inner silicon is melted and then cooled and solidified to produce crystalline silicon particles made of a polycrystal or single crystal excellent in crystallinity (see, for example, Patent Document 4).

WO99 / 22048 pamphlet U.S. Pat. No. 4,188,177 JP-A-5-78115 U.S. Pat. No. 4,430,150

  However, when silicon particles are heated to melt the silicon compound film formed on the surface thereof, specifically silicon inside the silicon oxynitride film and then solidified, the CZ (Czochralski) method is used. Since there is no solidification starting point like a seed crystal when growing a general bulk silicon single crystal such as the FZ (floating zone) method or the FZ (floating zone) method, solidification does not occur in one direction and polycrystallization due to the generation of many nuclei What happens is a problem. The polycrystallization of the crystalline silicon particles causes various problems as described above, and causes a problem that the characteristics of a photoelectric conversion device using the crystalline silicon particles for a photoelectric conversion element are deteriorated.

In addition, when using polycrystalline materials such as high-purity silicon synthesized in the vapor phase by the fluidized bed method for the production of crystalline silicon particles, the raw materials contained in the polycrystalline silicon and contamination from the manufacturing process are included. Contamination due to metal impurities such as iron and nickel, which are mainly caused by the above, becomes a problem. Since the metal impurity diffuses between the lattices which do not have a chemical bond in silicon, the impurity atoms are diffused through the gaps in the silicon lattice. This diffused metal impurity forms a deep level in silicon and acts as a carrier recombination center, causing an increase in leakage current and a decrease in lifetime, causing photodegradation.
That is, it is difficult to produce desired high-quality crystalline silicon particles by the conventional method for producing crystalline silicon particles, and a photoelectric conversion device having excellent electrical characteristics is produced using the obtained crystalline silicon particles. Therefore, there was a problem that it was unsuitable as a manufacturing method.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing crystalline semiconductor particles, which can stably crystallize semiconductor particles such as polycrystalline silicon and produce crystalline semiconductor particles having high crystallinity at low cost. Is to provide. Furthermore, it is providing the photoelectric conversion apparatus and photovoltaic device which were excellent in the electrical property using the crystalline semiconductor particle manufactured by the manufacturing method of the crystalline semiconductor particle.

  As a result of intensive studies to solve the above problems, the present inventors have formed a silicon compound film by placing the semiconductor particles on a silicon wafer when forming a silicon compound film on the surface of the semiconductor particles, By using a method for producing crystalline semiconductor particles having a predetermined thickness for the silicon compound film, the crystalline semiconductor particles are stably crystallized with high efficiency and at the same time, crystalline semiconductor particles having high crystallinity are produced at low cost. The inventors have found that this is possible and have completed the present invention.

That is, the method for producing crystalline semiconductor particles, the photoelectric conversion device, and the photovoltaic device in the present invention have the following configurations.
(1) In a method for producing crystalline semiconductor particles, in which a silicon compound film is formed on the surface of semiconductor particles, heated and melted, and then crystallized by cooling and solidifying, the semiconductor compound film is formed when the semiconductor compound film is formed. A method for producing crystalline semiconductor particles, wherein the particles are placed on a silicon wafer to previously form a silicon compound film.
(2) The method for producing crystalline semiconductor particles according to (1), wherein the silicon compound film has a thickness of 0.01 to 50 μm.
(3) The method for producing crystalline semiconductor particles according to (1) or (2), wherein the silicon compound film is silicon oxide or silicon oxynitride.
(4) A photoelectric conversion device in which a large number of semiconductor particles exhibiting one conductivity type are provided on a substrate, an insulator is provided between the semiconductor particles, and a semiconductor layer having a reverse conductivity type is provided on the semiconductor particles. And the said semiconductor particle is manufactured by the manufacturing method of the crystalline semiconductor particle in any one of (1)-(3), The photoelectric conversion apparatus characterized by the above-mentioned.
(5) A photovoltaic device using the photoelectric conversion device according to (4) as a power generation means and supplying the generated power of the power generation means to a load.

According to the above (1) to (3), when forming the silicon compound film on the surface of the semiconductor particles, the semiconductor particles are preliminarily formed by placing the semiconductor particles on the silicon wafer. The crystalline semiconductor can prevent the contamination and impurities from the base plate on which the semiconductor particles are placed from diffusing into the semiconductor particles when it is melted by the silicon compound film formed in advance before melting. The impurity concentration in the particles can be reduced, and the crystallinity of the crystalline semiconductor particles can be greatly improved.
Furthermore, the silicon compound coating formed on the surface of the semiconductor particles induces distortion at the interface between the surface of the semiconductor particles and the silicon compound coating, and when the semiconductor particles are heated and melted and solidified, metal impurities, etc. It becomes easy to diffuse in the strained layer induced by the formation of metal, and metal impurities and the like can be efficiently gettered.
According to the above (4), a large number of semiconductor particles exhibiting one conductivity type are disposed on a substrate, an insulator is disposed between the semiconductor particles, and a semiconductor layer exhibiting a reverse conductivity type is disposed on the semiconductor particles. A high-quality crystalline semiconductor having excellent electrical characteristics, since the crystalline semiconductor particles are produced by the method for producing crystalline semiconductor particles of the present invention having any one of the above-described structures. Particles can be produced, and mass production is inexpensive at low cost by stacking quartz base plates for processing in a heating furnace in multiple stages and placing silicon particles on the base plate with high density Since it can also be manufactured well, the efficiency and reliability of the photoelectric conversion device can be improved.
And according to said (5), since the photoelectric conversion apparatus of said this invention was used as an electric power generation means, and it came to supply the electric power generated by this electric power generation means to load, this book with high efficiency and high reliability. With the photoelectric conversion device of the invention, power generation capability is improved, and reliability can be secured stably over a long period of time.
As described above, according to the method for producing crystalline semiconductor particles of the present invention, it is possible to stably and efficiently crystallize a large number of crystalline semiconductor particles and easily mass-produce crystalline semiconductor particles having high crystallinity. Therefore, by using this, a good photoelectric conversion device excellent in photoelectric conversion characteristics and a photovoltaic device using the photoelectric conversion device can be provided.

Hereinafter, the manufacturing method of the crystalline semiconductor particle of this invention is demonstrated in detail, referring drawings.
1 (a) to 1 (e) are longitudinal sectional views for each process showing an outline of an example of an embodiment of a method for producing crystalline semiconductor particles of the present invention. In FIG. 1, 101 is a semiconductor particle or crystalline semiconductor particle (silicon particle or crystalline silicon particle), 102 is a base plate, 103 is a solidification starting point (one pole), and 104 is a silicon wafer. Reference numeral 101a denotes stress strain formed on the surface layer of semiconductor particles (crystalline semiconductor particles).

(Crystal silicon particles)
In the following embodiments, an example using silicon as a semiconductor material will be described.
First, semiconductor grade crystalline silicon is used as a semiconductor 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 101 are obtained.
The polycrystalline silicon particles 101 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 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.
At the time when the silicon particles 101 are obtained by this melting and dropping method, the shape of the silicon particles 101 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 manufactured using the polycrystalline silicon particles 101 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 101 and due to the carrier recombination effect at the polycrystalline grain boundaries. In order to remedy this, the polycrystalline silicon particles 101 are remelted in a temperature-controlled heating furnace by the method for producing crystalline semiconductor particles of the present invention, and then cooled and solidified, for example, in an oxygen / nitrogen atmosphere. Single crystal crystalline silicon particles 101 with a very low impurity content are used.

  In order to fabricate the single crystalline silicon particles 101, first, as shown in FIG. 1A, a large number of polycrystalline silicon particles 101 are placed on a silicon wafer 104 and heated (not shown). And the silicon particles 101 are heated to form a silicon compound film. It is desirable that the silicon particles 101 be filled and placed so that there is no gap as much as possible. However, the silicon particles 101 may be in contact with each other. Next, a large number of the obtained polycrystalline silicon particles 101 are placed side by side on the upper surface of the base plate 102. It is desirable that the silicon particles 101 are placed on the base plate 102 in a single layer. It is desirable that the silicon particles 101 be filled and placed so that there is no gap as much as possible. However, the silicon particles 101 may be in contact with each other. Further, the base plate 102 is preferably a plate-like one, and may be stacked in a plurality of stages. For the material of the base plate 102, quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire and the like are suitable for suppressing the reaction with the silicon particles 101, but the cost is excellent in heat resistance, durability, and chemical resistance. Quartz glass is preferred because it is cheap and easy to handle.

  In addition, the base plate 102 is used as a solidification starting point when the silicon particles 101 are cooled and solidified after being melted to be crystallized. By placing a large number of silicon particles 101 on the upper surface of the base plate 102 in this way, the solidification starting point 103 can be set at the contact portion between each silicon particle 101 and the base plate 102. 103 as one pole, the solidification (crystallization) direction can be set from this one pole 103 toward the upper opposing pole, and it is possible to solidify in one direction without using a seed crystal. Generation of grains and the like can be suppressed, and the crystallinity of the crystalline silicon particles 101 can be greatly improved.

  Since the size of the semiconductor particles 101 including the silicon particles 101 is usually almost spherical, the diameter of the particles is preferably 2000 μm or less, and the shape is preferably close to a sphere. However, the shape of the silicon particles 101 is not limited to a sphere, and may be a cubic shape, a rectangular parallelepiped shape, or other irregular shapes. When the size of the semiconductor particles 101 exceeds 2000 μm, a predetermined silicon compound film formed on the surface of the silicon particles 101 becomes relatively thin, so that the semiconductor particles 101 at the time of melting of the inner silicon are obtained. It is difficult to keep the shape of the film stable, and it is difficult to completely melt the silicon. If the melting is incomplete, subgrains are likely to be generated, which is not desirable. On the other hand, when the size of the silicon particle 101 is as small as less than 30 μm in diameter, the silicon particle 101 has a thin silicon compound film on the surface, which makes it difficult to maintain the shape during melting. It is not desirable because the silicon particles 101 arranged adjacent to each other are easily combined. Accordingly, the size of the semiconductor particles 101 is preferably 30 to 2000 μm, thereby suppressing the coalescence of the semiconductor particles 101 and maintaining the shape of the semiconductor particles 101 stably to generate subgrains. It is possible to stably produce a high quality crystalline silicon particle 101 having no spherical shape.

Next, as shown in FIG. 1B, the base plate 102 on which the silicon particles 101 are placed is introduced into a heating furnace (not shown), and the silicon particles 101 are heated, whereby the silicon particles 101. To melt. As the inside of the heating furnace, various types can be used depending on the type of the semiconductor material. However, if silicon is used as the semiconductor material, a resistance heating type or induction heating type atmosphere firing furnace used for firing ceramics or the like is used. Alternatively, a horizontal oxidation furnace or the like generally used in the semiconductor element manufacturing process is suitable. A resistance heating type atmosphere firing furnace used for firing ceramics is desirable because it is relatively easy to raise a temperature of 1500 ° C. or higher, and a large-sized one capable of mass production of the crystalline semiconductor particles 101 can be obtained at a relatively low cost. .
Prior to heating in the atmosphere firing furnace, it is desirable to perform solution cleaning in advance by the RCA method in order to remove metal, foreign matter, etc. adhering to the surface of the silicon particles 101. The RCA cleaning method is a cleaning method generally used in the manufacturing process of a semiconductor device as a standard cleaning process of a silicon wafer. In the first stage among the three stages, ammonium hydroxide and peroxide are used. The oxide film and silicon surface are removed with an aqueous solution of hydrogen water, the oxide film attached in the previous step is removed with hydrofluoric acid in the second step, and hydrogen chloride and peroxidation are removed in the third step. A natural oxide film is formed by removing heavy metals with an aqueous solution of hydrogen.

In order to prevent contamination from furnace materials and heating elements in the heating furnace, it is desirable to install a bell jar that covers the silicon particles 101 placed on the base plate 102 in the heating furnace. Quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for the material of the bell jar, but quartz glass is preferred because it is excellent in heat resistance, durability and chemical resistance, and is easy to handle at low cost. is there.
Note that argon, nitrogen, helium, and hydrogen are suitable for the inside of the bell jar in order to prevent re-adhesion contamination of organic substances and the like on the surface of the silicon particles 101, but from the viewpoint of low cost and easy handling, argon or Nitrogen is preferred.

(Silicon compound coating)
In the process of heating the silicon particles 101 while introducing a reactive gas composed of oxygen gas and nitrogen gas in a heating furnace and raising the temperature to a temperature higher than the melting point of silicon, A compound film is formed.
As the silicon compound film formed on the surface of the silicon particle 101, 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, and silicon particles such as contaminants and impurities are present. From the viewpoint that the diffusion preventing power to the inside of 101 is large, it is preferable to form a silicon oxynitride film (silicon oxynitride film).
Further, it is desirable that the oxygen partial pressure and the nitrogen partial pressure of the atmosphere in the heating furnace by the reactive gas when forming this silicon oxynitride film on the surface of the silicon particle 101 are 0.5% or more, respectively. When the oxygen partial pressure or nitrogen partial pressure in the atmospheric gas is less than 0.5%, the formation of the silicon oxynitride film formed on the surface of the silicon particles 101 that crystallize the inside becomes insufficient, and the silicon compound Undesirably, the coating tends to crack. In order to form only silicon oxide as the silicon compound film, it can be formed by setting the partial pressure ratio of nitrogen gas to oxygen gas to less than 0.1%.
In addition, each gas partial pressure in the atmospheric gas in a heating furnace can be adjusted with each gas flow rate with respect to the total gas flow rate. For example, the atmospheric gas is supplied from the gas supply means into the bell jar through the gas filter. Any device that supplies gas to the gas supply means may have a mechanism capable of adjusting the gas pressure and the gas concentration.

  As described above, the silicon particles 101 introduced into the heating furnace are heated below the melting point (1414 ° C.) of the semiconductor material to form a silicon compound film on the surface of the silicon particles 101. Next, the silicon particles 101 are heated to a temperature not lower than the melting point of the semiconductor material and not lower than the melting point of silicon, and preferably not higher than 1490 ° C. During this time, silicon inside the silicon compound film on the surface of the silicon particles 101 is melted. At this time, the silicon compound film formed on the surface of the silicon particles 101 can maintain the shape of the silicon particles 101 while melting the inner silicon. However, when the temperature of the semiconductor particles 101 is difficult to maintain stably, for example, in the case of the silicon particles 101, when the temperature is increased to a temperature exceeding 1490 ° C., when the silicon inside melts, It is difficult to keep the shape of the silicon particles 101 stable, and it is likely that coalescence with the adjacent silicon particles 101 is likely to occur, and a fusion reaction with the base plate 102 is likely to occur, which is not desirable.

  In the case of the silicon particles 101, the thickness of the silicon compound film formed on the surface is preferably 0.01 μm or more in the above particle diameter range (30 to 2000 μm). When the thickness is as thin as less than 0.01 μm, it is not desirable because the coating on the surface is easily broken when the silicon inside is melted. In addition, if the silicon compound film has a required strength with a thickness of 0.01 μm or more, the silicon inside tends to spheroidize with surface tension when it melts, whereas in the above temperature range, the silicon compound film Since it is sufficiently deformable, the crystalline silicon particles 101 obtained by internal crystallization can be formed 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 difficult to be deformed in the above temperature range, and the shape of the obtained crystalline silicon particles 101 is unlikely to be a shape close to a true sphere. Not desirable. Therefore, in the case of the silicon particles 101, the thickness of the silicon compound film on the surface thereof is preferably 0.01 to 50 μm with respect to the above-mentioned particle diameter range (30 to 2000 μm), thereby being close to a true sphere. Crystal silicon particles 101 having a good shape can be stably obtained, and a photoelectric conversion device having excellent conversion efficiency can be obtained by using the crystal silicon particles 101 for a photoelectric conversion element.

  Next, as shown in FIG. 1 (c), the molten semiconductor particles 101 are cooled down to a temperature of about 1400 ° C. or less below the melting point in order to solidify the molten silicon inside the silicon compound film in the silicon particles 101. Let it solidify. At this time, when solidifying in a relatively high temperature region below the melting point, solidification progresses in one direction toward the upper facing pole with the contact portion on the base plate 102 as the solidification starting point (one pole) 103. Therefore, the crystallinity of the solidification starting point 103 is inherited as it is by the entire semiconductor particle 101 and the crystal grows. Therefore, the obtained crystalline silicon particle 101 becomes a single crystal, and the crystallinity can be greatly improved.

  Further, during the solidification of the molten semiconductor particles 101, a thermal annealing process is performed on the semiconductor particles 101. For example, in the case of the crystalline silicon particles 101, a thermal annealing process is performed for 30 minutes or more at a constant temperature of 1000 ° C. or higher. It is desirable. By performing this thermal annealing treatment, the strain in the crystal of the crystalline semiconductor particles 101 generated at the time of solidification, the interfacial strain generated at the interface between the silicon compound film on the surface and the inner crystalline silicon, etc. are alleviated and removed. Crystalline crystalline semiconductor particles 101 can be obtained.

  In the method for producing crystalline semiconductor particles according to the present invention, the base plate 102 on which a large number of semiconductor particles 101 having a silicon compound film as described above are placed on the upper surface is introduced into a heating furnace. 1A to 1C, a process of heating and melting the semiconductor particles 101, and a process of solidifying the melted semiconductor particles 101 from the solidification starting point (one pole) 103 on the side of the base plate 102 toward the upper opposing pole. You may repeat twice or more as shown to (e). By repeating the melting step and the solidifying step in this manner, the low-concentration impurities remaining at the solidification starting point 103 and the central portion of the semiconductor particle 101 at the first time are further added to the solidification end portion (opposite pole). Since they can be integrated, the crystalline semiconductor particles 101 with higher purity can be obtained by etching away the terminal portion containing impurities at a higher concentration than the first time.

  In the case where the crystalline semiconductor particles 101 are crystalline silicon 101 and are used in a photoelectric conversion device, it is also effective to form fine irregularities on the surface of the crystalline silicon particles 101 in addition to the above. 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 the irregularities on the surface when the photoelectric conversion device is configured using the crystalline silicon particles 101 as a photoelectric conversion element. It will be a thing. Even if the surface irregularities are too large or too small, a sufficient effect cannot be expected, and by making the irregularities such that the arithmetic average roughness Ra of the surface is 0.01 to 5 μm, the photoelectric conversion device , The utilization efficiency of incident light can be satisfactorily improved by irregular reflection of light.

  According to the method for producing crystalline semiconductor particles of the present invention, the crystalline semiconductor particles 101 having good crystallinity and a reduced amount of unnecessary impurities can be stably produced as described above.

(Photoelectric conversion device)
Next, FIG. 2 shows a longitudinal sectional view of an example of an embodiment of the photoelectric conversion device of the present invention.
In FIG. 2, 206 is a crystalline silicon particle, 207 is a conductive substrate, 208 is a bonding layer between the crystalline silicon particle 206 and the conductive substrate 207, 209 is an insulating material, 210 is a semiconductor layer, 211 is a translucent conductor layer, 212 is an electrode.
In the photoelectric conversion device using the crystalline silicon particles 206 of the present invention, the second conductive material is formed on one main surface of the conductive substrate 207, in this example, the upper surface, on the surface of the first conductive type, for example, p-type crystalline silicon particles 206. A large number of crystalline silicon particles 206 having an n-type semiconductor layer 210, for example, are bonded to the conductive substrate 207 at the lower portion thereof by, for example, a bonding layer 208 and insulated between adjacent ones of the crystalline silicon particles 206. The material 209 is interposed and the upper part of the crystalline silicon particles 206 is disposed so as to be exposed from the insulating material 209, and the transparent conductive layer 211 is provided on the crystalline silicon particles 206. In addition, when using this photoelectric conversion apparatus as a solar cell, the electrode 212 is deposited and formed in a predetermined pattern shape on the translucent conductor layer 211, for example, a finger electrode and a bus bar electrode. .
In the photoelectric conversion device of the present invention, in such a configuration, the crystalline silicon particles 206 are manufactured by the method for manufacturing the crystalline semiconductor particles 101 of the present invention as described above. It is.
In the photoelectric conversion device of the present invention, since the crystalline silicon particles 206 are produced by the method for producing crystalline semiconductor particles of the present invention, it is possible to obtain a high-quality silicon material having an extremely low impurity concentration. Therefore, the minority carrier lifetime, which is an important factor for obtaining high photoelectric conversion efficiency, can be improved, and crystalline silicon particles 206 preferable as a material for forming a photoelectric conversion device can be obtained.

Next, the crystalline silicon particles 206 in the photoelectric conversion device of the present invention are produced in the same manner as the above-described method for producing the crystalline silicon particles 101. The silicon particles 101 used as a starting material for the crystalline silicon particles 206 are preferably doped with a p-type semiconductor impurity as a first conductivity type dopant so as to have a desired resistance value. As described above, boron, aluminum, gallium or the like is preferable as the p-type dopant, and the addition amount is preferably 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ .
The crystalline silicon particles 101 (206) manufactured by the above-described manufacturing method of the crystalline semiconductor particles 101 of the present invention are used for manufacturing the photoelectric conversion device of the present invention. The photoelectric conversion device can be used as a power generation unit, and a photovoltaic power generation device configured to supply the generated power from the power generation unit to a load can be obtained.

  The example shown in FIG. 2 is produced using the crystalline silicon particles 206 obtained as described above. In order to obtain this photoelectric conversion device, first, the silicon compound film formed on the surface of the obtained crystalline silicon particles 206 is removed by etching with hydrofluoric acid. The thickness of the silicon compound film removed at this time is 1 μm or more in the radial direction. Further, in order to remove the interfacial strain between the silicon compound film and the crystalline silicon particles 206 and the p-type dopant segregated on the surface of the crystalline silicon particles 206, impurities such as oxygen, carbon and metal, the surface of the crystalline silicon particles 206 is removed. Etching away with hydrofluoric acid or the like may be used. The thickness of the surface layer of the crystalline silicon particles 206 removed at that time is desirably 100 μm or less in the radial direction.

  Next, a second conductivity type semiconductor layer 210, for example, an n-type semiconductor layer 210 is provided on the surface of the crystalline silicon particles 206. The n-type semiconductor layer 210 is provided by forming an amorphous or polycrystalline semiconductor layer 210 or by forming the semiconductor layer 210 by thermal diffusion or the like. At this time, since the crystalline silicon particles 206 are p-type, the silicon layer 210 which is the semiconductor layer 210 is an n-type semiconductor layer 210.

Next, a large number of crystalline silicon particles 206 are arranged on the conductive substrate 207. Then, the crystalline silicon particles 206 are bonded to the conductive substrate 207 through the bonding layer 208 generated by heating the whole in a reducing atmosphere. The bonding layer 208 is, for example, an alloy of aluminum and silicon.
At this time, by using the conductive substrate 207 as a metal substrate including at least aluminum on the surface, the crystalline silicon particles 206 can be bonded at a low temperature, and a light-weight and low-cost photoelectric conversion device can be provided. In addition, by making the surface of the conductive substrate 207 rough, it is possible to randomly reflect the incident light in the non-light-receiving region that reaches the surface of the conductive substrate 207, and to reflect the incident light obliquely. Incident light can be used effectively by allowing the module surface to be re-reflected and further photoelectrically converting it at the photoelectric conversion part of the crystalline silicon particles 206.

Next, an insulating material 209 is placed on the conductive substrate 207 so as to be interposed between adjacent ones of the bonded crystalline silicon particles 206, and at least the zenith portion of the crystalline silicon particles 206 is formed from the insulating material 209. Place it exposed.
Here, the surface shape of the insulating material 209 between the adjacent crystalline silicon particles 206 is a concave shape in which the crystalline silicon particle 206 side is raised, so that the insulating material 209 and the top thereof are covered. The difference in refractive index from the sealing resin of the photoelectric conversion module applied in this manner can promote the irregular reflection of incident light on the crystalline silicon particles 206 in the non-light-receiving region where the crystalline silicon particles 206 as the photoelectric conversion material are not present. it can.

Next, a translucent conductor layer 211 is provided on the exposed upper portion of the crystalline silicon particles 206. And in order to take out desired electric power as a solar cell, silver paste etc. are apply | coated to the predetermined pattern shape, and electrodes 212, such as a grid electrode or a finger electrode and a bus-bar electrode, are formed. In this manner, by using the conductive substrate 207 as one electrode and the electrode 212 as the other electrode, a photoelectric conversion device as a solar cell can be obtained.
According to the photoelectric conversion device of the present invention as described above, since the effect of segregating impurities can be enhanced by repeating the melting and solidifying step twice or more, a large number of high-quality crystals with less impurities Silicon particles 206 can be manufactured with high productivity, and silicon materials used in the photoelectric conversion device can be used efficiently. At the same time, the high-quality granular silicon crystal 206 improves the efficiency and reliability of the photoelectric conversion device. Thus, a photoelectric conversion device with high efficiency and low cost can be provided.
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.

  EXAMPLES Hereinafter, although an Example is given and the manufacturing method and photoelectric conversion apparatus of the crystalline semiconductor particle 101 of this invention are demonstrated in detail, this invention is not limited only to a following example.

Hereinafter, a specific example of the method for manufacturing the crystalline semiconductor particles 101 of the present invention and the photoelectric conversion device using the crystalline silicon particles 206 manufactured thereby will be described along the manufacturing steps.
Quartz having a boron concentration of 0.6 × 10 ¹⁶ atoms / cm ³ and a large number of crystalline silicon particles 101 having a particle diameter of about 400 μm are placed on a silicon wafer 104 and placed inside a firing furnace as a heating furnace. A silicon oxynitride film is formed on the surface of the crystalline silicon particles 101 as a silicon compound film by being heated in the vicinity of 1300 ° C. while being introduced from a reactive gas supply means of oxygen gas and nitrogen gas while being contained in a bell jar.
Next, a large number of crystalline silicon particles 101 having a silicon oxynitride film formed thereon are placed on a quartz glass base plate 102 in one layer, and the inside of an atmosphere firing furnace filled with an argon inert atmosphere as a heating furnace. And heated while introducing a reaction gas of oxygen gas and nitrogen gas from the gas supply means, heated to 1440 ° C. above the melting point of silicon and held for 2 minutes. After the silicon inside the silicon oxynitride film was melted, it was solidified from the solidification starting point (one pole) 103 toward the other pole above while cooling at a temperature drop rate of 4 ° C. per minute. Thereafter, the temperature was further lowered to 1300 ° C., and a thermal annealing treatment for 200 minutes was performed. After this thermal annealing treatment, the temperature was lowered to around room temperature.
Next, the same process was performed again on the crystalline silicon particles 101 cooled to near room temperature, and the crystalline silicon particles 101 were produced by the method for producing the crystalline semiconductor particles 101 of the present invention.
At this time, the partial pressure with respect to the total gas flow rate of oxygen gas and nitrogen gas in the heating furnace when forming the silicon oxynitride film on the surface of the crystalline silicon particle 101 is 20% and 80%, respectively, and the oxygen gas with respect to the total gas flow rate The temperature drop rate was adjusted by controlling the temperature of oxygen gas and nitrogen gas.
The silicon oxynitride film formed on the surface of the recovered crystalline silicon particles 101 was removed with hydrofluoric acid, and the surface of the crystalline silicon particles 101 was etched away in the depth direction with hydrofluoric acid to a predetermined thickness (10 μm).
The crystalline silicon particles 101 are placed on a quartz boat and introduced into a quartz tube controlled at 900 ° C., POCL ₃ gas is bubbled with nitrogen and fed into the quartz tube, and the crystalline silicon particles 101 ( 206), an n-type semiconductor layer 210 having a thickness of about 1 μm was formed, and then the silicon oxynitride film on the surface was removed with hydrofluoric acid.
Next, as shown in FIG. 2, an aluminum substrate having a size of 50 mm × 50 mm × thickness 0.3 mm is used as the conductive substrate 207, and the crystalline silicon particles 206 are arranged on the upper surface in a close-packed manner, and then aluminum and silicon are used. The lower part of the crystalline silicon particles 206 was bonded to the conductive substrate 207 by heating in a reducing atmosphere furnace of nitrogen containing 5% hydrogen at 600 ° C. exceeding the eutectic temperature of 577 ° C. . At this time, a bonding layer 208 made of a eutectic of aluminum and silicon was formed in a portion where the crystalline silicon particles 206 were in contact with aluminum of the conductive substrate 207, and exhibited strong adhesive strength.
Further, from above, the upper portions of the crystalline silicon particles 206 are exposed to each other, and an insulating material 209 made of polyimide is applied and dried to form a conductive substrate 207 serving as a lower electrode, and a light-transmitting conductive layer serving as an upper electrode. 211 is electrically insulated and separated.
On this, a translucent conductor layer 211 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 disperser to form an electrode 212 composed of finger electrodes and bus bar electrodes, and a photoelectric conversion device according to the present invention was produced. The silver paste pattern was fired at 500 ° C. in the atmosphere.

  As an example of the present invention, as shown in FIG. 1, the silicon compound film was formed on the silicon wafer 104 in advance on the silicon particles 101 of the present invention. Crystalline silicon particles 206 were produced, and a photoelectric conversion device was produced using them (sample Nos. 1 to 5). However, Sample No. Nos. 1 and 5 have a silicon compound film thickness outside the scope of the present invention.

  Next, as a comparative example, a silicon compound film is directly formed on the quartz base plate 102 to produce crystalline silicon particles 206 having the thickness of the silicon compound film shown in Table 2, and a photoelectric conversion device using them. (Sample Nos. 6 to 10).

表１に示す通り、比較例として石英製の台板１０２上にシリコン粒子１０１を載置してシリコン粒子１０１表面に珪素化合物被膜を形成した場合（試料Ｎｏ．８）に比較して、本発明の実施例で作製した、シリコンウェーハ１０４上にシリコン粒子１０１を載置してシリコン粒子１０１表面に珪素化合物被膜を形成した場合（試料Ｎｏ．３）では、比較例に比べてＦｅの不純物濃度が減少し、良好な結果であった。 (Measurement method and measurement results)
Impurities in the crystalline silicon particles 206 obtained above were sampled. 3 and 8 were examined. The impurity concentration was measured using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) (manufactured by Micromass). The film thickness of the silicon compound film was measured using a fluorescent X-ray film measuring apparatus (manufactured by Philips). The results are shown in Table 1. The silicon compound film was confirmed to be silicon oxynitride by measurement using ICP-MS.

As shown in Table 1, as a comparative example, the present invention is compared with the case where silicon particles 101 are placed on a quartz base plate 102 and a silicon compound film is formed on the surface of the silicon particles 101 (sample No. 8). In the case where the silicon particles 101 are placed on the silicon wafer 104 and the silicon compound film is formed on the surface of the silicon particles 101 (sample No. 3), the impurity concentration of Fe is higher than that of the comparative example. It was decreased and was a good result.

表２に示す通り、石英製の台板１０２上にシリコン粒子１０１を載置してシリコン粒子１０１表面に珪素化合物被膜を形成し、溶融・凝固させて結晶シリコン粒子２０６としたものから成る光電変換装置（試料Ｎｏ．５〜１０）に比較して、本発明で作製した、シリコンウェーハ１０４上にシリコン粒子１０１を載置してシリコン粒子１０１表面に本発明の範囲内の膜厚の珪素化合物被膜を形成した場合の光電変換装置（試料Ｎｏ．２〜４）では、光電変換効率が高く良好な結果であった。また、珪素化合物被膜の膜厚を変えて比較した場合、シリコンウェーハ１０４上および石英製の台板１０２上で珪素化合物被膜を形成した場合共に、珪素化合物被膜が０．０１〜５０μｍの範囲で光電変換効率が高く良好な結果であった。 Next, about the obtained photoelectric conversion apparatus (sample No. 1-10), the light of predetermined intensity | strength and predetermined wavelength was irradiated, and the photoelectric conversion efficiency (unit:%) which shows an electrical property was measured. The measurement of electrical characteristics was carried out by a method based on JIS C 8913 using a solar simulator (WACOM: WXS155S-10). The results are shown in Table 2.

As shown in Table 2, a photoelectric conversion comprising a silicon particle 101 placed on a quartz base plate 102 to form a silicon compound film on the surface of the silicon particle 101 and melted and solidified to form a crystalline silicon particle 206. Compared with the apparatus (sample Nos. 5 to 10), the silicon compound film having a film thickness within the range of the present invention is placed on the surface of the silicon particle 101 by placing the silicon particle 101 on the silicon wafer 104 produced in the present invention. In the photoelectric conversion device (Sample Nos. 2 to 4) in the case of forming, the photoelectric conversion efficiency was high and good results. Further, when the thickness of the silicon compound film is changed and compared, both in the case where the silicon compound film is formed on the silicon wafer 104 and the quartz base plate 102, the silicon compound film is in the range of 0.01 to 50 μm. The conversion efficiency was high and good results were obtained.

  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 method of melting the semiconductor particles 101 by irradiating light energy such as laser light from the upper part of the semiconductor particles 101 placed on the upper surface of the base plate 102 is used to heat and melt the semiconductor particles 101 instead of a heating furnace. In that case, since the melting and solidifying step can be repeated with the atmosphere as a vacuum atmosphere, the entry of oxygen or the like from the atmospheric gas into the crystalline semiconductor particles 101 can be suppressed.

It is a longitudinal cross-sectional view for every process which shows schematic structure of an example of embodiment about the manufacturing method of the crystalline semiconductor particle of this invention. It is a longitudinal cross-sectional view which shows an example of embodiment about the photoelectric conversion apparatus of this invention.

Explanation of symbols

101 ... Semiconductor particles or crystalline semiconductor particles (silicon crystals or crystalline silicon particles)
101a ... Stress strain 102 formed on the surface layer ... Base plate 104 ... Silicon wafer 206 ... Crystalline silicon particles 207 ... Conductive substrate 208 ... Bonding layer 209 ... Insulating substance 210 ... Semiconductor layer 211 ... Translucent conductor layer 212 ... Electrode

Claims (5)

  In a method for producing crystalline semiconductor particles, in which a silicon compound film is formed on the surface of the semiconductor particles, heated and melted, and then cooled and solidified to crystallize the semiconductor particles when the silicon compound film is formed. A method for producing crystalline semiconductor particles, comprising placing a silicon compound film on a wafer.   The method for producing crystalline semiconductor particles according to claim 1, wherein the silicon compound film has a thickness of 0.01 to 50 μm.   The method for producing crystalline semiconductor particles according to claim 1, wherein the silicon compound film is silicon oxide or silicon oxynitride.   A photoelectric conversion device in which a large number of semiconductor particles exhibiting one conductivity type are provided on a substrate, an insulator is provided between the semiconductor particles, and a semiconductor layer having a reverse conductivity type is provided on the semiconductor particles. The said semiconductor particle is manufactured by the manufacturing method of the crystalline semiconductor particle in any one of Claims 1-3, The photoelectric conversion apparatus characterized by the above-mentioned. 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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