MX2008008923A - Methods and apparatuses for manufacturing geometric multicrystalline cast silicon and geometric multicrystalline cast silicon bodies for photovoltaics - Google Patents
Methods and apparatuses for manufacturing geometric multicrystalline cast silicon and geometric multicrystalline cast silicon bodies for photovoltaicsInfo
- Publication number
- MX2008008923A MX2008008923A MXMX/A/2008/008923A MX2008008923A MX2008008923A MX 2008008923 A MX2008008923 A MX 2008008923A MX 2008008923 A MX2008008923 A MX 2008008923A MX 2008008923 A MX2008008923 A MX 2008008923A
- Authority
- MX
- Mexico
- Prior art keywords
- silicon
- crucible
- plate
- multicrystalline
- optionally
- Prior art date
Links
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Abstract
Methods and apparatuses are provided for casting silicon for photovoltaic cells and other applications. With such methods and apparatuses, a cast body of geometrically ordered multi-crystalline silicon may be formed that is free or substantially free of radially-distributed impurities and defects and having at least two dimensions that are each at least about 10 cm is provided.
Description
METHODS AND APPARATUS FOR MANUFACTURING MONO-CRYSTALLINE GEOMETRIC CAST SILICONE AND CAST SILICON BODIES
GEOMETRIC MONOCRYSTALLINE FOR PHOTOVOLTAIC CELLS
FIELD OF THE INVENTION The present invention relates generally to the field of photovoltaic cells and methods and apparatuses for manufacturing molten silicon for photovoltaic applications. The invention is further related to new forms of molten silicon that can be used to make devices such as photovoltaic cells and other semiconductor devices. The new silicon can have a geometrically ordered multicrystalline structure and can be manufactured by a casting process.
BACKGROUND OF THE INVENTION Photovoltaic cells convert light into electric current. One of the most important measures of a photovoltaic cell is its efficiency in converting light energy into electrical energy. Although photovoltaic cells have been manufactured from a variety of semiconductor materials, silicon is generally used because it is readily available at a reasonable cost and because it has an adequate balance of electrical, physical and chemical properties for use in the manufacture of REF. . : 194466
Photovoltaic cells. In a known process for the production of photovoltaic cells, the silicon raw material is mixed with a material (or adulterant) to induce a conductivity of positive or negative type, it is melted and then crystallized either by extraction by pulling the crystallized silicon of a zone fused in monocrystalline silicon ingots (via the Czochralski (CZ) or flotation zone (FZ) methods) or melted into blocks or bricks of multicrystalline silicon or polycrystalline silicon, depending on the grain size of the grains of individual silicon. In the process described in the foregoing, ingots or blocks are cut into thin substrates, also referred to as planks, by known slicing or sawing methods. These plates are then processed in photovoltaic cells. Monocrystalline silicon for use in the production of photovoltaic cells is generally produced by the CZ or FZ methods, both processes in which a cylindrically shaped bolus of crystalline silicon is produced. For a CZ procedure, the bolus is slowly pulled out from a pool of molten silicon. For a FZ process, the solid material is fed through a melting zone and resolidified on the other side of the melting zone. A bolus of monocrystalline silicon, manufactured
in this way, it contains a radial distribution of impurities and defects such as oxygen-induced stacking failure rings (OSF) and "wavy" defects of interstitial or free groups. Even with the presence of these impurities and defects, monocrystalline silicon is generally a preferred source of silicon to produce photovoltaic cells because it can be used to make high efficiency solar cells. However, monocrystalline silicon is more expensive to produce than conventional multicrystalline silicon, using known techniques such as those described above. Conventional multicrystalline silicon for use in the production of photovoltaic cells is generally produced by a casting process. The melting process for preparing conventional multicrystalline silicon is known in the art of photovoltaic technology. Briefly, in the process, the molten silicon is contained in a crucible such as a quartz crucible and is cooled in a controlled manner to allow crystallization of the silicon contained therein. The block of multicrystalline silicon that results is usually cut into bricks that have a cross section that is equal to or close to the size of the plate to be used for manufacturing a photovoltaic cell and the bricks are cut or sliced in some other way in said plates.
The multicrystalline silicon produced in this way is an agglomeration of crystal grains where, within the plates made therefrom, the orientation of the grains in relation to one another is effectively random. The random orientation of the grains, either in conventional multicrystalline silicon or in polycrystalline silicon makes it difficult to texturize the surface of the resulting plate. Texturing is used to improve the efficiency of a photovoltaic cell by reducing light reflection and improving the absorption of light energy through the surface of the cell. Additionally, the "deformations" that are formed in the boundaries between conventional multicrystalline silicon grains tend to nuclear structural defects in the form of groups or lines of dislocations. These dislocations and the impurities they tend to attract are considered to cause a rapid recombination of the electric charge carriers in a functioning photovoltaic cell made of conventional multicrystalline silicon. This can cause a decrease in the efficiency of the cell. The photovoltaic cells made of multicrystalline silicon generally have a lower efficiency compared to equivalent photovoltaic cells made of monocrystalline silicon, even considering the radial distribution of defects present in monocrystalline silicon produced by
known techniques. However, due to the relative simplicity and lower fabrication costs of conventional multicrystalline silicon as well as the efficient passivation of defects in cell processing, multicrystalline silicon is a more widely used form of silicon for the manufacture of photovoltaic cells. Some previous smelting techniques involve using a "cold wall" crucible for the growth of crystals. The term "cold wall" refers to the fact that induction coils present on or within the walls of the crucible are cooled with water, and may also be grooved and thus generally remain below 100 ° C. The walls of the crucible can be located in close proximity between the coils and the raw material. The material of the crucible walls is not particularly thermally insulating and therefore can remain in thermal equilibrium with the cooled coils. The heating of the silicon therefore does not impair the radiation of the crucible walls because the inductive heating of the silicon in the crucible means that the silicon is heated directly by induced current to flow therein. In this way the walls of the crucible remain below the melting temperature of the silicon and are considered "cold" in relation to the molten silicon. During solidification of silicon
Inductively heated cast, the use of cold walls of the crucible acts as a heat sink. The ingot cools quickly, determined by radiation from cold walls. Therefore, an initial solidification front quickly becomes substantially curved with crystal nucleation which occurs on the sides of the ingot and which grows diagonally towards the center of the ingot, interrupting any attempt to maintain a vertical and geometrically sowing procedure ordered or a substantially flat solidifying front. In view of the foregoing, there is a need for an improved form of silicon that can be used to manufacture photovoltaic cells. There is also a need for silicon that can be manufactured in a process that is faster and less expensive than the procedures that have hitherto been used to make monocrystalline silicon. The present invention provides the silicon and the processes.
SUMMARY OF THE INVENTION As used herein, the term "monocrystalline silicon" refers to a single crystal silicon body having a consistent crystalline orientation therethrough. In addition, conventional multicrystalline silicon refers to crystalline silicon having a grain size distribution at cm scale with crystals
randomly oriented multiple ones that are located inside a silicon body. Furthermore, as used herein, the term "polycrystalline silicon" refers to crystalline silicon with grain size of the order of micrometers and multiple grain orientations that are located within a given body of silicon. For example, grains are typically an average of about one size submicron to submillimeter (for example individual grains may not be visible to the naked eye) and grain orientation is randomly distributed thereon. Furthermore, as used herein, the term "nearly monocrystalline silicon" refers to a crystalline silicon body having a consistent crystal orientation through more than 50 volume% of the body where, for example, silicon Almost monocrystalline may be constituted by a single crystal silicon body close to a multicrystalline region or it may be constituted by a large and contiguously consistent crystal of silicon partially or completely containing smaller crystals of silicon of other crystalline orientations, wherein the smallest crystals do not constitute more than 50% of the total volume. Preferably, the almost monocrystalline silicon may contain smaller crystals which do not constitute more than 25% of the volume
total. More preferably, the almost monocrystalline silicon may contain smaller crystals which do not constitute more than 10% of the total volume. Even more preferably, the almost monocrystalline silicon may contain smaller crystals which do not constitute more than 5% of the total volume. However, as used herein, the term "geometrically ordered multicrystalline silicon" (hereinafter abbreviated as "geometric multicrystalline silicon") refers to crystalline silicon, according to the embodiments of the present invention having a size distribution of grain to scale of cm ordered geometrically, with multiple ordered crystals located within the body of silicon. For example, in geometric multicrystalline silicon, each grain typically has an average cross-sectional area of about 0.25 cm 2 to about 2,500 cm 2 in size where the cross section in the plane is perpendicular to the height or length of the grain and a height that can be as large as the silicon body, for example, the height can be as large as the body dimension of the silicon that is perpendicular to the plane of the cross section, with the grain orientation inside a body of controlled multicrystalline silicon according to predetermined orientations. The shape of the section
The cross-section of the grain that is perpendicular to the height or length of the grain of the multicrystalline geometric silicon is typically the same as the shape of the seed crystal or part of a seed crystal on which it is formed. Preferably, the shape of the cross section of the grain is polygonal. Preferably, the corners of the polygonal beads correspond to joints of three different grains. Although each grain within a multicrystalline geometric silicon body preferably comprises silicon having a consistent glass orientation contiguous through the grain, one or more grains may also contain small amounts of smaller silicon crystals of different orientation. For example, each of the grains may partially or completely contain smaller crystals of silicon from other crystal orientations where the smaller crystals do not constitute more than 25% of the total grain volume, preferably not more than 10% of the total volume of the grain, more preferably not more than 5% of the total grain volume, still more preferably not more than 1% of the total grain volume and much more preferably not more than 0.1% of the total grain volume. According to the invention, as it is constituted and described generally, there is provided a method for manufacturing molten silicon comprising: placing a geometric distribution of a plurality of crystals of
sowing monocrystalline silicon on at least one surface in a crucible having one or more side walls heated to at least the melting temperature of the silicon and at least one wall for cooling; placing molten silicon in contact with the geometric distribution of seed crystals of monocrystalline silicon; and forming a solid body of geometrically ordered multicrystalline silicon, which optionally has at least two dimensions each is at least about 10 cm, upon cooling the molten silicon to control crystallization, wherein the shaping includes controlling a solid boundary. liquid at the edge of the molten silicon during cooling, so that it moves in a direction that increases a distance between the molten silicon and at least one wall for cooling. It is contemplated that one of the walls of the crucible may be the bottom of the crucible. According to one embodiment of the present invention, there is also provided a method for manufacturing molten silicon comprising: distributing a plurality of monocrystalline silicon seed crystals in a predetermined pattern over at least two surfaces of a crucible having one or more side walls heated to at least the melting temperature of the silicon and at least one wall for cooling; placing molten silicon in contact with the plurality of silicon seed crystals
monocrystalline; and forming a solid body of geometrically ordered multicrystalline silicon, optionally having at least two dimensions, each being at least about 10 cm, by cooling the molten silicon from at least two surfaces of the crucible to control the crystallization, in where the formation includes controlling a solid-liquid boundary on the edge of the molten silicon during cooling so as to move the boundary in a direction that increases the distance between the molten silicon and the monocrystalline silicon seed crystals in the crucible. According to another embodiment of the present invention there is also provided a method for manufacturing molten silicon comprising: placing a geometric distribution of a plurality of seed crystals of mincrystalline silicon on at least one surface in a crucible; placing silicon raw material in contact with the plurality of monocrystalline silicon seed crystals on at least one surface; heating the silicon raw material and the plurality of monocrystalline silicon seed crystals to the melting temperature of the silicon; controlling the heating so that the plurality of seed crystals of monocrystalline silicon is not completely melted, the control comprises maintaining a? T of about 0.1 ° C / min or less, measured on the
outer surface of the crucible, after reaching the melting temperature of the silicon elsewhere in the crucible; and once the plurality of seed crystals have partially melted, form a solid multicrystalline silicon body geometrically ordered by cooling the silicon. According to still another embodiment of the present invention there is also provided a method of manufacturing molten silicon comprising: distributing a plurality of monocrystalline silicon seed crystals in a predetermined pattern on at least two crucible surfaces; placing the silicon raw material in contact with the plurality of monocrystalline silicon seed crystal on at least two surfaces; squirt the silicon raw material and the plurality of monocrystalline silicon seed crystals up to the melting temperature of the silicon; controlling the heating so that the plurality of seed crystals of monocrystalline silicon is not completely melted, the control comprises maintaining a ΔT of about 0.1 ° C / min or less, measured on the external surface of the crucible, after reaching the temperature of fusion of silicon elsewhere in the crucible; and, once the plurality of seed crystals have partially melted, form a solid body of geometrically ordered multicrystalline silicon
by cooling the silicon. According to a further embodiment of the present invention there is also provided a method for manufacturing molten silicon comprising: placing at least one geometric multicrystalline silicon seed crystal on at least one surface in a crucible having one or more side walls heated to at least the melting temperature of the silicon and at least one wall for cooling; placing molten silicon in contact with at least one seed crystal; and forming a solid body of geometrically ordered multicrystalline silicon, optionally having at least two dimensions, each being at least about 10 cm, by cooling the molten silicon to control crystallization, wherein the formation includes controlling the solid boundary liquid at an edge of the molten silicon during cooling so that it moves in a direction that increases the distance between the molten silicon and at least one seed crystal of geometric multicrystalline silicon in the crucible. According to still another embodiment of the present invention there is also provided a method for manufacturing molten silicon comprising: placing a geometric distribution of a plurality of monocrystalline silicon seed crystals on at least one surface in a crucible, the plurality of crystals from
seeding of monocrystalline silicon are distributed to cover all or substantially all of the area of at least one surface in the crucible; placing molten silicon in contact with the geometrical distribution of monocrystalline silicon seed crystals and forming a solid body of geometrically ordered multicrystalline silicon which optionally has at least two dimensions, each being at least about 10 cm by cooling the molten silicon to control crystallization. According to still another embodiment of the present invention there is also provided a method for manufacturing molten silicon comprising: placing molten silicon in contact with at least one geometric multicrystalline silicon seed crystal in a vessel having one or more heated side walls at least the silicon melting temperature, at least one geometrically arranged multicrystalline silicon seeding crystal distributed to cover all or substantially all of the area of a container surface; and forming a solid body of geometrically ordered multicrystalline silicon which optionally has at least two dimensions, each being at least about 10 cm by cooling the molten silicon to control crystallization.
According to a further embodiment of the present invention there is also provided a geometrically continuous multicrystalline silicon body having a predetermined distribution of grain orientations, the body optionally further having at least two dimensions wherein each is at least about 10 cm and a third dimension of at least about 5 cm. According to yet another embodiment of the present invention there is also provided a geometrically melted and continuous multicrystalline silicon body having a predetermined distribution of grain orientations, the body optionally having at least two dimensions which are each at least approximately 10 cm. According to a further embodiment of the present invention there is also provided a geometrically continuous multicrystalline ordered silicon sheet having a predetermined distribution of grain orientations, the sheet further having at least two dimensions wherein each is at least approximately 50 mm According to a further embodiment of the present invention there is also provided a solar cell comprising: a plate formed of a multicrystalline silicon body ordered geometrically continuous, the body
has a predetermined distribution of grain orientations preferably with a common pole direction that is perpendicular to a body surface, the body further has at least two dimensions wherein each is optionally of at least about 10 cm and a third dimension of at least about 5 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the iron; optionally at least one layer that is selected from the back surface field and a passivating layer; and electrically conductive contacts on the plate. According to a further embodiment of the present invention there is also provided a solar cell comprising: a plate formed of a multicrystalline silicon body arranged continuously geometrically melted, the body having a predetermined distribution of grain orientations preferably with a common pole direction which is perpendicular to a surface of the body, the body further has at least two dimensions which are each optionally at least about 10 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the plate; optionally at least one layer that is selected from a back surface field and a passivating layer; and electrically conductive contacts on the plate.
According to a further embodiment of the present invention there is also provided a solar cell comprising: a continuous geometrically ordered multicrystalline silicon sheet having a predetermined distribution of grain orientations preferably as a common pole direction which is perpendicular to a surface of the iron, the iron also has at least two dimensions and are each at least approximately 50 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the iron; optionally at least one layer that is selected from a back surface field and a passivating layer; and electrically conductive contacts on the plate. According to a further embodiment of the present invention there is also provided a plate comprising: silicon formed from a continuously geometrically ordered multicrystalline silicon body, the body having a predetermined distribution of grain orientations preferably with a common pole direction that is perpendicular to a surface of the body, the body further has at least two dimensions which are each optionally at least about 10 cm and a third dimension of at least about 5 cm. According to an additional modality of the
present invention there is also provided a plate comprising: silicon formed from a multicrystalline silicon body continuously geometrically melted, the body has a predetermined distribution of grain orientations preferably with a common pole direction that is perpendicular to a body surface , the body further has at least two dimensions wherein each is optionally of at least about 10 cm. According to a further embodiment of the present invention there is also provided a plate comprising: a continuous geometrically ordered multicrystalline silicon plate having a predetermined distribution of grain orientations preferably with a common pole direction that is perpendicular to a surface of the iron, the iron also has at least two dimensions where each is at least about 50 mm. According to a further embodiment of the present invention there is also provided a solar cell comprising: a plate sliced from a continuously geometrically ordered multicrystalline silicon body, the body having a predetermined distribution of grain orientations preferably with a pole direction common that is perpendicular to a surface of the body, the body also has at least two dimensions where each one is
optionally of at least about 10 cm and a third dimension of at least about 5 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the iron; optionally at least one optional layer that is selected from the back surface field and a passivating layer; and a plurality of electrically conductive contacts on at least one surface of the plate. According to a further embodiment of the present invention there is also provided a solar cell comprising: a plate sliced from a multicrystalline silicon body arranged continuously geometrically melted, the body has a predetermined distribution of grain orientations preferably with a direction of common pole that is perpendicular to a surface of the body, the body furthermore has at least two dimensions which are each optionally of at least about 10 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the iron; optionally at least one optional layer that is selected from a back surface field and a passivating layer; and a plurality of electrically conductive contacts on at least one surface of the plate. According to a further embodiment of the present invention there is also provided a solar cell which
comprises: a geometrically continuous multicrystalline ordered silicon plate having a predetermined distribution of grain orientations preferably with a common pole direction that is perpendicular to a surface of the plate, the plate further having at least two dimensions wherein each of at least about 50 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the iron; at least one optional layer that is selected from a back surface field and a passivating layer; and a plurality of electrically conductive contacts on at least one surface of the plate. According to another embodiment of the present invention, the nearly monocrystalline silicon of the present invention made according to the invention can contain up to 5% by volume of smaller crystals of silicon from other crystal orientations. Preferably, according to another embodiment of the present invention, the nearly monocrystalline silicon made in accordance with the invention can contain up to 1% by volume of smaller crystals of silicon of other crystalline orientations. Even more preferably, according to another embodiment of the present invention, the almost monocrystalline silicon made according to the invention can contain up to 0.1% by volume of smaller silicon crystals of other
crystal orientations. The additional features and advantages of the invention will be established in the description that follows, being evident from the description or learned by the practice of the embodiments of the invention. The features and other advantages of the invention will be realized and will be obtained by the structures of semiconductor devices and methods and manufacturing apparatus highlighted particularly in the written description and in the claims as well as in the appended claims. It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are designed to provide a further explanation of the invention as claimed. This invention also includes silicon made by the methods described and claimed herein and plates and solar cells made from silicon.
BRIEF DESCRIPTION OF THE FIGURES The appended figures, which are incorporated and constitute a part of this specification illustrate embodiments of the invention and together with the description serve to explain the characteristics, advantages and principles of the invention. In the drawings: Figure 1 illustrates an exemplary distribution of
silicon seeds on the bottom surface of a crucible, according to one embodiment of the present invention; Figure 2 illustrates another exemplary distribution of silicon seeds on the bottom and side surfaces of a crucible, in accordance with one embodiment of the present invention; Figure 3A to Figure 3C illustrate an example of tile roofing for casting geometrically ordered multicrystalline silicon in a crucible according to an embodiment of the present invention; Figure 4 illustrates another example of tile coating for melting multicrystalline silicon arranged geometrically in a crucible, according to one embodiment of the present invention; Figure 5 illustrates an example of a tight packed arrangement of hexagonal seed tiles, according to one embodiment of the present invention; Figure 6 illustrates an exemplary distribution of polygonal shapes having rhomboidal or triangular interstices, according to one embodiment of the present invention; Figure 7 illustrates an exemplary method according to an embodiment of the present invention; and Figure 8A to Figure 8G and Figure 9 illustrate exemplary casting procedures for silicon
monocrystalline or multicrystalline ordered geometrically according to embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or similar reference numbers will be used in the drawings to refer to the same or similar parts. In the embodiments according to the invention, the crystallization of the molten silicon is carried out by a melting process using one or more seed crystals. As described herein, the casting processes can be implemented so as to control the size, shape and orientation of the crystal grains in the casting body of the crystallized silicon. As used herein, the term "molten" means that the silicon is formed by molten silicon cooled in a mold or container used to retain the molten silicon. Since a liquid, such as molten silicon, will take on the shape of the container in which it is placed, it is also contemplated herein that the cooling of the molten silicon can also be carried out while confining the molten silicon by any means and not only in a
mold or container. By way of example, the silicon can be formed by solidification in a crucible, wherein the solidification is initiated from at least one wall of the crucible and not through a foreign cooling object introduced into the melt. The crucible can have any suitable shape such as a cup, a cylinder or a box. Therefore, the crystallization process of molten silicon according to this invention is not controlled by "pulling" a bolus or ribbon. Furthermore, in a manner consistent with one embodiment of the present invention, the mold, container or crucible includes at least one "hot side wall" surface in contact with the molten silicon. As used herein, the term "hot side wall" refers to a surface that is isothermal or that is hotter than the molten silicon with which it has contact. Preferably, the hot side wall surface remains fixed during silicon processing. Consistent with the embodiments of the invention, the crystallized silicon can be continuous, almost monocrystalline or continuous multicrystalline geometric monocrystalline silicon having controlled grain orientations. As used herein, the term "continuous monocrystalline silicon" refers to a single crystal silicon, wherein the silicon body is a homogeneous body of monocrystalline silicon and not smaller pieces of silicon attached
to form a larger piece of silicon. Further, as used herein, the term "continuous geometric multicrystalline silicon" refers to the multicrystalline geometric silicon wherein the silicon body is a homogeneous body of geometric multicrystalline silicon and not smaller pieces of silicon that join to form a largest piece of silicon. Consistent with the embodiments of the present invention, the crystallization can be carried out by placing a desired collection of crystalline silicon "seeds", for example, at the bottom of a container, such as a quartz crucible that can hold molten silicon. . As used herein, the term "seed" (seeding) refers to a piece of silicon preferably geometrically shaped with a desired crystal structure, preferably wherein at least one cross section has a geometric shape, preferably polygon and preferably having a side that adapts to the surface of a container in which it can be placed. Said seed may be a monocrystalline piece of silicon or a piece of multicrystalline silicon arranged geometrically, for example, a plate or a cut in horizontal section or obtained in some other way from a geometrically ordered monocrystalline silicon ingot. Consistent with the present invention, a seed may have a
upper surface that is parallel to its lower surface although this does not need to be the case. For example, a seed may be a piece of silicon that varies in size from about 2 mm to about 3000 mm across. For example, a seed can be from about 10 mm to about 300 mm across. The silicon part can have a thickness from about 1 mm to about 1000 mm, preferably from about 5 mm to about 50 mm. A suitable size and shape of the seeds can be selected for comfort and tile roofing. The shingle coating, which will be described in more detail in the following, is when the silicon seed crystals are distributed in a predetermined geometrical orientation or pattern through, for example, the bottom of one or more of the sides and the sides. bottom surfaces of a crucible. It is preferable that the seed or seeds cover all the surfaces of the crucible near which they are located so that when the seed crystal is moved the solidification by growth moves away from the seeds, the full size of the cross section of the crucible it can be maintained as a matching geometric crystal. The molten silicon is then allowed to cool and crystallize in the presence of the seeds, preferably in such a way that the cooling of the molten silicon is brought to
This is done so that the crystallization of the molten silicon starts at or below the level of the original top of the solid seeds and moves away, preferably moving upwards from the seeds. The solid-liquid boundary at one edge of the molten silicon will preferably be initially adapted to a cooling surface of the container such as a surface in a crucible in which it has been melted. According to embodiments of the invention, the liquid-solid boundary between the molten silicon and the crystallized silicon can be maintained substantially flat through a part, for example the initial part of the solidification step or throughout the casting process . In one embodiment of the invention, the solid-liquid boundary at each of the edges of the molten silicon is controlled during cooling so that it moves in a direction that increases a distance between the molten silicon and the cooled surface of a crucible while which preferably maintains a substantially flat solid-liquid boundary. Therefore, in accordance with the present invention, the solidification front can be parallel to the shape of the cooled surface of the container. For example, with a flat bottom crucible, the solidification front may remain substantially flat where the solid-liquid boundary has a controlled profile. He
Solid-liquid boundary can be controlled so that its radius of curvature decreases as one moves from edge to center. Alternatively, the solid-liquid limit can be controlled to maintain an average radius of curvature of half the width of the container. In addition, the solid-liquid limit can be controlled to maintain an average radius of curvature of at least twice the width of the container. The solid may have a slightly convex boundary with a radius of curvature at least about four times the width of the container. For example, the solid-liquid boundary may have a radius of curvature generally greater than 2 m in a square crucible of 0.7 m, more than twice the horizontal dimension of the crucible and preferably approximately 8x to approximately 16x a horizontal dimension of the crucible . According to embodiments of the present invention, a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably molten silicon, preferably having at least two dimensions, each of which is at least about 20 cm, for example, can be formed. less about 20 cm on one side and a third dimension of at least about 10 cm. Preferably, a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably melted having at least two, can be formed.
dimensions, each is at least about 30 cm, for example, of at least about 30 cm on one side and a third dimension of at least about 10 cm. More preferably, a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably molten silicon, having at least two dimensions, each of which is at least about 35 cm, for example, at least about 35 cm in diameter, can be formed. one side and one third dimension, of at least about 10 cm. Even more preferably a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably molten silicon, having at least two dimensions, each of which is at least about 40 cm, for example at least about 40 cm in diameter, can be formed. one side and one third dimension of at least about 20 cm. Even more preferably, a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably cast, having at least two dimensions, each of which is at least about 50 cm, for example, at least about 50 cm, can be formed. on one side, and a third dimension of at least about 20 cm. Even more preferably, a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably molten silicon, can be formed, which
less two dimensions, each is at least about 60 cm, for example, at least about 50 cm on one side and a third dimension, of at least about 20 cm. Even more preferably, a solid body of monocrystalline silicon or almost monocrystalline silicon, preferably molten silicone having at least two dimensions, each of which is at least about 70 cm, for example, at least about 70 cm in diameter, can be formed. one side and one third dimension of at least about 20 cm. The upper limit of the horizontal size of a molten silicon longue made according to the embodiments of the invention is determined solely by the technology of casting and making crucibles and not by the invented method itself. Ingots having a cross-sectional area of at least 1 m2 and up to 4-8 m2 can be manufactured according to this invention. Similarly, the upper limit of the height of the ingot can be related to longer cycle times and not to the foundations of the casting process. Ingot heights of up to approximately 50 cm to approximately 80 cm are possible. Thus, according to the invention, a continuous monocrystalline silicon body or nearly monocrystalline silicon can be successfully grown to approximately 66 cm x 66 cm in cross section, with a
rectangular solid piece of continuous monocrystalline silicon that is at least 33,750 cm3 in volume. Furthermore, according to the present invention, a solid body of molten continuous monocrystalline silicon or almost monocrystalline silicon can be formed which preferably has at least two dimensions, each being as large as the internal dimensions of the casting container and the third dimension is the same height as the ingot. For example, if the monocrystalline silicon casting body has a cube shape or a solid of rectangular shape, these previous dimensions make reference to the length, width and height of the bodies. Similarly, a solid body of multicrystalline geometric silicon, preferably melted geometric multicrystalline silicon, preferably has at least two dimensions, each of at least about 10 cm and a third dimension of at least about 5 cm, can be formed. Preferably, a solid body of fused multicrystalline geometric silicon, preferably of fused multicrystalline geometric silicon having at least two dimensions, each of at least about 20 cm and a third dimension of at least about 5 cm, can be formed. More preferably, a solid multicrystalline silicon multicrystalline silicon body can be formed
fused, preferably cast, geometric having at least two dimensions, each is at least about 30 cm and a third dimension at least about 5 cm. Even more preferably, a solid multicrystalline geometric multicrystalline silicon silicon body may be formed, preferably having at least two dimensions, each being at least about 35 cm and a third dimension of at least about 5 cm. cm. Even more preferably, a solid multicrystalline geometric multicrystalline silicon silicon body may be formed, preferably having at least two dimensions, each being at least about 40 cm and a third dimension of at least about 5 cm. cm. Even more preferably, a solid multicrystalline geometric silicon multicrystalline silicon body, preferably cast, having at least two dimensions, each of at least about 50 cm and a third dimension of at least about 5 cm, can be formed. cm. More preferably, a solid body of multicrystalline geometric silicon can be formed of a molten multicrystalline, preferably molten silicon body having at least two dimensions, each being at least about 60 cm and a third dimension of at least less approximately 5
cm. More preferably, a solid multicrystalline geometric silicon multicrystalline silicon body preferably having a geometrically melted silicon having at least two dimensions, each of at least about 70 cm and a third dimension of at least about 5 cm. Thus, consistent with the invention, a continuous geometric multicrystalline silicon body can successfully grow up to approximately 66 cm x 66 cm in cross section, with a solid rectangular piece of continuous geometric monocrystalline silicon that is at least 33,750 cm3 in diameter. volume. Furthermore, according to the present invention, a solid body of molten multicrystalline geometric silicon, preferably a molten multicrystalline silicon, preferably having at least two dimensions, each being as large as the internal dimensions of the casting container, can be formed. For example, if the geometric multicrystalline silicon melting body is a cube-shaped solid or a rectangular shape, the above dimensions can refer to the length, width and height of the bodies. By carrying out the crystallization of the molten silicon in a manner consistent with the embodiments of the invention, molten silicon having specific grain boundaries, instead of random and specific grain sizes, can be made. Additionally, when aligning one or several
of the seeds so that all the seeds are oriented in the same relative direction to each other, for example the pole direction (100) that is perpendicular to the bottom of the crucible and the pole direction (110) parallel to one of the sides of a crucible of rectangular or square cross section, large bodies of molten silicon can be obtained which are of monocrystalline or near silicon, in which the pole direction of the molten silicon is the same as that of the seeds. Similarly, other pole directions may be perpendicular to the bottom of the crucible. In addition, according to one embodiment of the invention, one or more of the seeds can be distributed so that any direction of common pole is perpendicular to the bottom of the crucible. When monocrystalline silicon is made by the conventional method of pulling a cylindrically shaped bolus from an accumulated molten silicon, for example, according to the CZ or FZ method, the monocrystalline silicon obtained contains impurities and radially distributed defects such as as wavy defects (formed from intrinsic defects such as voids and autointerstitial atoms) and OSF ring defects. Wavy defects are interstitial or hollow silicon atoms, either singly or clustered. Waviness defects can be detected by X-ray topography, and
they appear as "wavy" in silicon. They can also be detected after attack by preferential acid etchant of silicon for defect delineation. According to conventional CZ or FZ methods, the distribution of oxygen atoms within silicon and defects in silicon caused by oxygen atoms are located radially. This means that they tend to be distributed in rings, spirals or grooves that are symmetrical around the central axis. OSF ring defects are a particular example of this, where nanometer-scale oxygen precipitates filament faults nucleated in a cylindrical band within an extracted monocrystalline ingot or silicon bolus, resulting in circular defect bands on plates made from silicon. Said bands can be observed in a sample of silicon after attack by preferential acid etchant. Both wavy defects and OSF ring defects are present in monocrystalline silicon boluses when pulling a cylindrically shaped bolus from an accumulated molten silicon, for example in accordance with conventional CZ or FZ methods, due to the rotational symmetry of the Pull procedure, axial thermal gradients and the inherent rotation in the procedure. In contrast, silicon can be made by casting procedures
according to the embodiments of the invention which do not show the wavy defects and OSF ring defects. This is due to the incorporation of defects during the casting process can be distributed essentially randomly at the growth limit unaltered by rotation in a silicon body that does not possess cylindrical symmetry and in procedures where the isotherms are essentially flat to through the ingot through the solidification and cooling procedures. With respect to the concentrations of the impurities of the light element in silicon that is grown by different methods, the following levels, which are shown in table 1, are considered to be broadly characteristic. TABLE 1
The parts of the CZ ingots can be produced with an amount as low as 5 x 1017 atoms / cm3 of oxygen but not less. Carbon and nitrogen concentrations can be increased in FZ and CZ ingots by adulteration
intentional, but the adulteration does not exceed the limit of solid solubility in these techniques (as it does in the molten material) and the adulterated ingots have not been made if the size is greater than 20 cm in diameter. By contrast, the molten ingots are typically supersaturated with carbon and nitrogen due to the design release coatings of the hot zone of the furnace. As a consequence, precipitated nitrides and carbides are ubiquitous due to nucleation and liquid phase growth. In addition, the single molten glass ingots have been manufactured according to the embodiments of the invention with impurity concentrations reported in the foregoing and with sizes as large as 50 x 50 x 20 cm3 and 60 x 60 x 5 cm3. These dimensions are only exemplary and are not considered upper limits for the casting process of the invention. For example, a concentration of dissolved carbon of about 1-5 x 1017 atoms / cm3 (notation for about 1 x 1017 atoms / cm3 to about 5 x 1017 atoms / cm3) is preferred over a concentration of impurity, a concentration of dissolved oxygen of about 2-3 x 1017 atoms / cm 3 and a dissolved nitrogen concentration of about 1-5 x 10 15 atoms / cm 3 are preferred in the silicon melt according to this invention. In accordance with the modalities of this
invention can be formed into a solid multicrystalline geometric silicon body, preferably fused multicrystalline geometric silicon and preferably having at least two dimensions, each being at least about 10 cm, and a third dimension of at least about 5 cm. cm, having a dissolved carbon concentration of approximately 1-5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Preferably a solid body of multicrystalline geometric silicon, preferably fused multicrystalline geometric silicon and having at least two dimensions, each is at least about 20 cm, and a third dimension of at least about 5 cm, can be formed. it has a dissolved carbon concentration of approximately 1-5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Preferably, a solid body of multicrystalline geometric silicon, preferably melted geometric multicrystalline silicon and having at least two dimensions, each is at least about 30 cm, and a third dimension of at least about 5 cm, can be formed. has a concentration of
dissolved carbon of approximately 1-5 x 10 atoms / cm, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Even more preferably, a solid body of multicrystalline geometric silicon, preferably fused multicrystalline geometric silicon and having at least two dimensions, each of at least about 35 cm, and a third dimension of at least one can be formed. about 5 cm, which has a dissolved carbon concentration of approximately 1-5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Even more preferably, a solid body of multicrystalline geometric silicon, preferably fused multicrystalline geometric silicon and having at least two dimensions, each is at least about 40 cm, and a third dimension of at least one can be formed. about 5 cm, which has a dissolved carbon concentration of approximately 1-5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Even more preferably, a solid silicon body can be formed
multicrystalline geometric, preferably fused multicrystalline geometric silicon and having at least two dimensions, each is at least about 50 cm, and a third dimension of at least about 5 cm, having a dissolved carbon concentration of about 1 -5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Even more preferably, a solid body of multicrystalline geometric silicon, preferably fused multicrystalline geometric silicon and having at least two dimensions, each is at least about 60 cm, and a third dimension of at least one can be formed. about 5 cm, which has a dissolved carbon concentration of approximately 1-5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. Even more preferably, a solid body of multicrystalline geometric silicon, preferably fused multicrystalline geometric silicon and having at least two dimensions, each is at least about 70 cm, and a third dimension of at least one can be formed. approximately 5 cm, which has a concentration of carbon
dissolved from approximately 1-5 x 1017 atoms / cm3, a dissolved oxygen concentration of approximately 2-3 x 1017 atoms / cm3 and a dissolved nitrogen concentration of approximately 1-5 x 1015 atoms / cm3. The upper limit of the horizontal size of a molten silicon ingot made according to the embodiments of the invention and having the impurity concentrations referred to in the foregoing is determined solely by the melting and processing technology of the crucible and not by the same invented method. Thus, according to the invention, a solid body of continuous multicrystalline geometric silicon can successfully grow up to approximately 66 cm x 66 cm in cross section with a rectangular solid piece of continuous multicrystalline geometric silicon that is at least 33,750 cc in volume. Further, in accordance with the present invention, a solid body of multicrystalline geometric silicon preferably melted geometric multicrystalline silicon can be preferably formed with at least two dimensions, each being as large as the inside dimensions of a melt container. For example, if the casting body of the multicrystalline silicon is cube-shaped or is a solid of rectangular shape, these dimensions mentioned above refer to the length, width and height of the bodies.
One or more of the seeds used for casting processes, according to the embodiments of the invention can be of any desired size and shape but are usually geometrically shaped parts of monocrystalline silicon, nearly monocrystalline silicon or geometrically ordered multicrystalline silicon such as silicon pieces with square, rectangular, hexagonal, rhomboid or octagonal shape. Conductors can be formed for tile roofing so that they can be placed or "covered with tiles" edge to edge and can be shaped to the bottom of a crucible in a desired pattern. Also according to the embodiments of the invention, the seeds can be placed on one or more, including all sides of the crucible. Said seeds can be obtained, for example, by slicing a source of crystalline silicon such as a bolus of monocrystalline silicon into pieces having more desired shapes. The seeds can also be shaped by cutting them from a continuous or nearly monocrystalline monocrystalline silicon sample, or continuous geometric multicrystalline silicon made by a process according to the embodiments of the invention in such a way that one or more of the seeds for use in processes Subsequent castings can be made from an initial casting process. Thus, for example, a continuous or almost continuous monocrystalline silicon plate
Monocrystalline cut or otherwise obtained from a continuous or almost monocrystalline monocrystalline silicon ingot can function as a template for the subsequent casting of continuous or almost monocrystalline monocrystalline silicon. The seed crystal may have the size and shape or substantially the size and shape of a side such as the bottom of a crucible or other container in which the seed is placed. For the purpose of monocrystalline casting, it is preferable to have as few seeds as possible to cover the bottom of the crucible in order to avoid the incorporation of defects. In this way, the seed or seeds may have a size and shape or substantially the size and shape of one or more sides such as the bottom of a crucible or other vessel in which the seed or seeds are placed to perform the method of casting according to this invention. Now the methods and apparatus for preparing silicon according to some embodiments of the invention will be described. However, it should be understood that these are not just ways of forming silicon consistent with the principles of the invention. With reference to Figure 1 the seeds 100 are placed in the bottom of a crucible 110 with bottom and walls, such as a quartz crucible in such a way that they make close contact in the same orientation so that
they form a large and continuously oriented plate 120. Alternatively, they are placed in close contact in erroneous orientations selected in advance in order to produce specific grain boundaries with deliberately selected grain sizes in the resultant silicon that is produced. That is, for casting of multicrystalline geometric silicon the grain size in cross-section and preferably the cross-sectional shape of the resulting multicrystalline geometric crystallized silicon will be equal to or close to that of the seeds and the grain height can be as large as the size of the grain. silicon that is perpendicular to the cross section. If a geometric multicrystalline seed crystal is used, for example a geometric multicrystalline silicon plate cut or otherwise obtained from a geometric multicrystalline silicon ingot, the seed crystal or the seed crystals for coating the multicrystalline geometric silicon, the grain size in cross section and preferably the cross-sectional shape of the beads of the resulting multicrystalline geometric silicon will approximate the seeds grains or the multicrystalline geometric seeds. In this way, a geometric multicrystalline silicon plate cut or otherwise obtained from a geometric multicrystalline silicon ingot can be a "seed crystal"
of multicrystalline geometric silicon "(also referred to as a" geometrically ordered multicrystalline silicon seed crystal ") and can function as a template for a subsequent casting of multicrystalline geometric silicon The seed crystal may have the size and shape or substantially the size and shape of a side, such as the bottom of the crucible or other containers in which the seed is placed When the seed crystal is used in the method of this invention, the resulting multicrystalline geometric silicon will preferably have crystal grain having a size and shape in cross section equal or substantially equal to the grains in the seed Preferably, the seeds 100 are coated as shingles and placed so as to cover substantially the entire bottom of the crucible 110. It is also preferable that the crucible 110 Thong a release coating such as one made of silica, silicon nitride or A liquid encapsulant to assist in the separation of the crystallized silicon from the crucible 110. In addition, the seeds may comprise a monocrystalline silicon plate or plates of a desired crystal orientation of about 3 mm to about 100 mm in thickness. Although a specific number and size of seeds 100 is shown in Figure 1, it will be readily apparent to a person ordinarily skilled in the art that both the number and the size of the
Seeds can increase or decrease, depending on the application. With reference to Figure 2, the seeds 100 may also be placed in one or more lateral walls 130, 140 of the crucible 110. The seeds 100 may be placed in the entirety of the four walls of the crucible 110, but only for purposes of illustration the seeds 100 are only shown on the walls 130, 140. Preferably, the seeds 100 that are placed on any of the four walls of the crucible 110 are columnar to facilitate the growth of the crystal. Preferably, each of the columnar seeds placed on any of the four walls of the crucible 110 will have the same grain orientation as the seed placed immediately below on the bottom surface of the crucible 110. In case of growth of the multicrystalline geometric silicon, the placement of the columnar seeds in this way will facilitate the growth of multicrystalline geometric silicon grains as large as the height of the crucible 110. Still with reference to Fig. 2, the advantages of this seed distribution 110 are faster, simpler procedures of self-propagation for the casting of silicon with greater crystallinity and higher growth rates. For example, silicon can be melted into a "cup" of silicon consisting of many seeds that are
they stack together to form a cavity, for example the bottom and the four walls within the crucible 110. Alternatively, molten silicon can be poured into a silicon "cup" consisting of many seeds that are stacked together to form a cavity, for example the bottom and the four walls within the crucible 110. In an alternative example, the receiving "cup" is first brought to the melting temperature of the silicon but is maintained in the solid state and then the molten silicon is poured and allowed to It is placed in thermal equilibrium. Then, in any of the above examples, the crucible 110 is cooled so that heat is extracted from the bottom-and sides of the crucible 110, for example, by a solid thermal dissipating material (not shown) which radiates heat to the environment while the heat is still applied to the open top of the crucible 110. In this way, the molten ingot resulting from the silicon can be monocrystalline or multicrystalline geometric (depending on the type of seeds 100 used and their orientation) and the crystallization is carried out faster than in the known multicrystalline casting processes. To repeat this procedure, a portion of the bottom sides of the crystallized silicon ingot is extracted using known techniques and can be reused in a subsequent casting process. Preferably, a plurality of seed crystals, for example seeds 100 are
they distribute so that a common pole direction between the seeds 100 is perpendicular to each of the bottom and the sides of the crucible 110 so that no grain boundaries are formed between the bottom and one side of the crucible 110. Figure 3A to FIG. 3C illustrate an example of shingle coating for the casting of geometric multicrystalline silicon in a crucible 110. The manipulated glass grain can be obtained by the careful creation, orientation, placement and growth of seed glass. Figure 3A and Figure 3B, for example, show two plates 155, 165 of monocrystalline silicon on which different directions (110) are indicated. Both plates have a common direction (100) perpendicular to their surfaces. Each monocrystalline silicon plate 155, 165 is then cut to form many pieces of silicon which become seeds 150, 160. The surface types may be uniform, for example (100) for textural reasons or may be selected at will . The shape and size of the grains can be selected based on the cutting of the tiles from the monocrystalline silicon plates 155 and 165, as shown in Figure 3B. The relative orientation angles between neighboring tiles of the pieces 150, 160 determine the type of grain boundary (eg high angle, low angle or twins) in the resulting multicrystalline fused silicon. In the figure
3A, for example, two grain orientations of the pole direction (100) are shown. The seeds shown in Figure 3C in this way are comprised of monocrystalline silicon pieces coated as tiles 150, 160 having the orientation ratios selected specifically with their neighboring tiles. The silicon pieces 150, 160 are then coated as tiles in the bottom of the crucible 110, which is shown in Figure 3C so that the two directions (110) are alternating, as shown by the arrows drawn on the pieces 150, 160. It is important to note that the pieces 150, 160 are drawn as approximately square blocks solely for illustrative purposes and for the reasons stated in the foregoing, but may have other forms. Although not shown in Figures 3C, the seeds can also be located on the sides of the crucible, as in Figure 2. The silicon raw material (not shown) can then be introduced into the crucible 110 on the pieces 150, 160 and then it melts. Alternatively, the molten silicon can be poured into a crucible 110. In the alternative example, the crucible 110 is first brought to a temperature very close to or above the melting temperature of the silicon and then poured into the same molten silicon . Consistent with the modalities of the
invention a thin layer of seeds can be melted before solidification begins. Then, in any previous example, the crucible 110 is cooled, whereby heat is extracted from the bottom of the crucible 110 (and the sides only without the seeds are coated with tiles on the side surfaces as well), for example, by a dissipating material solid thermal which radiates heat to the environment while the heat is still applied to the open top of the crucible 110. In this way, the molten silicon is introduced while the seed remains as a solid and the directional solidification of the melt causes growth toward above the columnar grains. In this way, the molten ingot resulting from geometric multicrystalline silicon will mimic the grain orientations of siliconized seeds 150, 160 coated as tiles. Once this technique is implemented properly, the resulting ingot can be cut, for example, into horizontal plates to act as seed layers for other casting processes. The plate can have, for example, the size and shape or substantially the size and shape of a surface such as the bottom of a crucible or other container used for casting. For example, only one of said plates can be used for a casting process. Figure 4 illustrates a variation of the coating
with tiles shown in figure 3C. As an example of grain orientation for melted geometric multicrystalline silicon, the sowing pieces 150, 160 are coated as tiles with a common pole direction (001) that is perpendicular to the bottom of the crucible 110. In Figure 4 all the variations of the address family (110) are represented in the coating by shingles of the pieces 150, 160, as indicated by the directional arrows. Although not shown in this particular figure, the seeds can be on one or more sides of the crucible 110. Thus, the orientation of the seed crystals in a crucible used to form the silicon can be selected so that the specific grain boundaries they are formed in fused multicrystalline geometric silicon and where grain boundaries enclose geometric shapes. In contrast to the embodiments of the invention, the known melting processes involve the melting of multicrystalline grains in an uncontrolled manner by directional solidification from a completely melted silicon mass. The resulting grains basically have a random size orientation and distribution. Random grain orientation makes it difficult to effectively texturize the silicon surface. In addition, it has been demonstrated that the deformations in the grain boundaries, the natural products of the typical growth technique,
they tend to generate nuclei of structural defects that involve groups of dislocation lines. These dislocations and the impurities that tend to attract cause rapid recombination of electrical carriers and the degradation of functioning as a photovoltaic material. Therefore, in accordance with one embodiment of the invention, careful planning and sowing of a regular grain limit network for casting of monocrystalline or multicrystalline geometric silicon is carried out in such a way that the size, shape and orientation of the grains it is explicitly selected to maximize the carrier duration time and obtain impurities while minimizing structural defects. The grain boundaries can be selected to be uniform planes in order to minimize nucleation of dislocation and at the same time maintain vertical direction during growth. Grain boundary types are selected to maximize impurities and stress release. Grain orientations (especially surface orientation) are selected to allow texturing, improve surface passivation and increase grain strength. The size of the grains is selected to optimize the balance between effective collection distances and large absorption areas. For example, the casting of multicrystalline silicon
The geometry can be carried out in such a way that the multicrystalline geometric silicon can have a minimum average grain cross-sectional size of at least about 0.5 cm to about 10 cm with a common pole direction that is perpendicular to the surface of the multicrystalline silicon. fused geometric, as shown, for example, in Figures 3C and 4. The cross-sectional size of average glass grain can be from about 0.5 cm to about 70 cm or greater. As described above, the cross-sectional size is understood as the longest dimension of the grain cross-section that is perpendicular to the height or length of the grain. The net result is a general increase in the efficiency of the resulting photovoltaic material. According to one embodiment of the invention, a geometric distribution of a plurality of seed crystals of monocrystalline silicas can be placed on at least one surface in a crucible, for example a bottom surface of a crucible, wherein the geometrical distribution includes tightly packed polygons. Alternatively, a geometric distribution of a plurality of monocrystalline silicon seed crystals can be placed in such a way that the geometric distribution includes tightly packed hexagons or shapes
polygonals having rhomboid or triangular interstices as shown, for example, in Figures 5 and 6. In another further alternative, instead of using a plurality of monocrystalline seed crystals, a section or plate of silicon cut or obtained can be used. in some other manner of an ingot produced in an anterior cast of geometrically ordered multicrystalline silicon used as a single seeding crystal for the melting of geometrically ordered multicrystalline silicon in accordance with this invention. The single geometrical multicrystalline silicon seed crystal can be the same size and shape or substantially the same size and shape as the surface of the crucible or other container used to carry out the casting. More specifically, Figure 5 illustrates an example of a tightly packed distribution of hexagons 170. In contrast, Figure 6 illustrates an example of a distribution of polygonal shapes having rhomboidal or triangular interstices 180, 190. Both distributions are described with more detail in the following. Any of the distributions mentioned in the above is also applicable to a casting mode of either a solid or monocrystalline silicon body, a solid body of almost monocrystalline silicon or a solid body of multicrystalline geometric silicon, wherein the seed crystals are placed in such a way in the background and
the lateral surfaces of a crucible. The silicon crystal grains produced by casting a geometric multicrystalline silicon body, according to the embodiments of the invention, can be grown in a columnar manner. In addition, the crystal grains may have a cross section that is or is close to the shape of the seed from which it is formed. When making silicon that has specifically selected grain boundaries, preferably the grain limit junctions only have three grain boundaries that coincide in a corner. As shown in Figure 5, hexagonal arrays of seed crystals 170 are desirable for seed tile shingling where the orientation of the crystal is such that the atoms in the horizontal plane have three multiples or six multiples of symmetry such as (111) for silicon. In this way, Figure 5 illustrates a plan view of a portion of a hexagonal shaped seed collection for distribution at the bottom of a suitable crucible, such as that shown in Figures 1 and 2. The arrows indicate the orientation of the direction (110) of the silicon crystal in the seeds. Alternatively, orientations with 4 multiples of symmetry can be used with a different geometric configuration of the seeds to maintain stable and symmetric grain boundaries through
multiple grains and still satisfy the three corner grain boundary rule. For example, yes ? is a bad orientation between the direction (110) and the primary sides of an octagon with a pole (100) is already the vertex angle of an interstitial diamond, as shown in figure 6, all crystal grains will have a limit grain symmetric with respect to the direction (110) if a = 90 ° -?. In this example, all the crystal grains have a pole direction (100) perpendicular to the plane of the paper in which figure 6 is shown. In this way, figure 6 is a plan view of a portion of a collection of seeds in octagonal form together with diamond-shaped seeds 180, 190 for distributions in the bottom of a suitable crucible, such as that shown in figures 1 and 2. The arrows indicate the orientation of the direction (110) of the crystal of silicon in the seeds. Figure 7 is a flow diagram showing an exemplary method of silicon processing, in accordance with the present invention. Consistent with FIG. 7, method 700 can begin by selecting monocrystalline silicon seed crystals for monocrystalline or multicrystalline geometric silicon growth and distribution of monocrystalline silicon seed crystals in a crucible (steps 705). Alternatively, a plate cut or obtained in some other way from a silicon ingot
Monocrystalline or monocrystalline silicon ordered geometrically can be used as a single seed crystal. Subsequently, silicon raw material can be added to the crucible (step 710). The crucible is then heated from the top while the bottom of the crucible is cooled from the bottom (either passively or actively, see step 715). During the melting, the melting stage of the silicon is monitored to monitor and control the position of the solid-liquid boundary (step 720). The melting step of the silicon is allowed to take place until a portion of the monocrystalline silicon seed crystals are melted (step 725). Once a desired portion of the monocrystalline silicon seed crystals is melted, the melting step ends and the crystal growth stage begins (step 730). The growth of the crystal is allowed to continue unidirectionally and vertically within the crucible until the crystallization of silicon is complete (step 735). If the seeds are distributed for geometric multicrystalline silicon growth, the crystallization of step 735 will produce a multicrystalline geometric silicon ingot with columnar grains (step 740). Alternatively, if the seeds are distributed for monocrystalline silicon growth, the Crystallization of step 735 will produce a monocrystalline silicon ingot (step 745). Finally,
the ingot produced in any of steps 740 or 745 is separated for further processing (step 750). As shown in Figure 8A, the silicon raw material 200 can be introduced into the crucible 210 containing the seeds 220, for example, in one of two ways. In the first, the crucible 210 is loaded to its full capacity with raw material 200 of solid silicon, suitably in the form of conveniently sized pieces and the loaded crucible 210 is placed in a casting station (not shown). As shown in Figure 8B, the thermal profile in the crucible 210 is adjusted so that the upper part of the silicon charge in the crucible 110 is heated to melting while the bottom is actively or passively cooled to maintain the solid phase of the seeds 220 at the bottom of the crucible 210, that is to say, so that they do not float when the raw material 200 is melted. A solid heatsink material 230 is in contact with the bottom of the crucible 210 to radiate heat to the walls cooled by Water. For example, the heat sink material 230 may be a solid block of graphite and may preferably have dimensions as large or larger than the bottom of the crucible. According to the invention, for example, the heat sink material can be 66 cm by 66 cm by 20 cm when it is used with a crucible having a lower surface that is 66 cm by
66 cm. The side walls of the crucible 210 are preferably not cooled in any way provided that the seeds 220 are located only at the bottom of the crucible 210. In the seeds 220 the sides of the crucible 210, the dissipative material 230 are located at the bottom. The heat should be placed both on the bottom and on the sides of the crucible 210 to maintain the desired thermal profile. The melting phase of the silicon raw material 200 is closely monitored to monitor the position of the boundary between the molten silicon and the seeds. Preferably, the melt 240 (shown in Figure 8B) advances until all of the raw material silicon 200 except for the seeds 220 is completely melted, after which the seeds 220 partially melt. For example, the heating can be controlled closely so that the seeds 220 do not melt completely, by maintaining a ΔT of about 0.1 ° C / min or less, measured on the outer surface of the crucible, after reaching the temperature of fusion of silicon elsewhere in the crucible. Preferably, the heating can be tightly controlled by maintaining a ΔT of about 0.05 ° C / min or less, measured on the outer surface of the crucible, after reaching the melting temperature of the silicon elsewhere in the crucible. For example, consistent with the invention, the? T can be
measuring on the outer surface of the crucible between the crucible and a large block of graphite and a dipstick can be inserted into the melt 240 to measure the depth of the melt in order to calculate the portion of seeds 220 that have been melted. As shown in Figure 8C, the portion 250 illustrates a molten portion of the total thickness of the seeds 220 below the melt 240. After a portion 250 of the seeds 220 melts below the melt 240, the melt stage then it ends quickly and the crystal growth stage begins, wherein the heating in the upper part of the crucible 210 decreases and / or the cooling of the bottom in the material 230 heat sink increases. As an example of this procedure, the diagram shown in Figure 8D illustrates the melting of a portion 250 of seed 220 as a function of time. As shown in Figure 8B, a portion of the seeds having an initial thickness between 5 and 6 cm gradually melts to just under 2 cm of the solid seed remnants. For example, the heating can be closely controlled so that the seeds 220 do not completely melt while maintaining a ΔT of about 0.1 ° C / min or less, measured on the outer surface of the crucible (for example through a mounted thermocouple). in the cooling block) after reaching the temperature of
fusion of silicon elsewhere in the crucible. Preferably, the heating can be tightly controlled by maintaining a ΔT of about 0.05 ° C / min or less, measured on the outer surface of the crucible, after reaching the melting temperature of the silicon elsewhere in the crucible. At this point, the melting step ends quickly and the crystal growth stage begins, which is indicated by the comparative increase in the solid thickness measured in the ordinate of the diagram. Then, as shown in Figure 8E, the seeded crystal growth grows unidirectionally and vertically, within the crucible 210 until the crystallization of the silicon is complete. The casting cycle ends when the thermal gradient from the upper part to the lower part inside the crucible 210 has been uniformed. Then, the complete ingot 260 is cooled slowly to room temperature. For the casting of geometric multicrystalline silicon, as shown in Figure 8E, this unidirectional growth sown produces columnar-shaped grains 270 which generally have a horizontal cross-section which is the shape of the individual seed 220 on which it is formed. In this way, the grain boundaries of the melted geometric multicrystalline silicon can be selected in advance. Any of the
Sowing patterns / shingle coatings described above is applicable to this casting process. Alternatively, for the casting of monocrystalline silicon, seed distribution 220 can be processed to have no grain limit, resulting in molten monocrystalline silicon. As shown in Figure 8F, the portion 250 illustrates a molten portion of the total thickness of the seeds 220, below the melt 240. After a portion 250 of seed 220 melts below the melt 240, the melting step then it ends quickly and the crystal growth stage begins, where the heating of the upper part of the crucible 210 decreases and / or the cooling of the lower part of the material 230 heatsink increases. Then, as shown in Figure 8G, the. Sown glass growth continues unidirectionally and vertically, inside the crucible 210 until the crystallization of the silicon is complete. A substantially flat solid-liquid boundary 285 preferably propagates upward and away from the bottom surface of the crucible 210. The casting cycle ends after completion of crystal growth when the thermal gradient from the top and bottom inside the 210 glass has been uniformed. Then, the entire ingot 280 is cooled slowly to room temperature. For the casting of silicon
monocrystalline, as shown in Figure 8G, this seeding unidirectional growth produces a continuous solid body of molten monocrystalline silicon 290. In another method, which is illustrated in Figure 9, the silicon raw material 200 may be first melted in a separate compartment or a separate melt container 300. The seeds 220 may or may not partially melt from the top before the molten raw material 305 is fed or poured into the crucible 210 via the melt pipe 310, after which the cooling and growth is carried out as described. with reference to Figure 8B to Figure 8G. In another embodiment, the silicon seed crystals can be mounted on the walls of the crucible 210 (not shown) and the sown growth can be carried out from the sides as well as from the bottom of the crucible 210, as previously described. Alternatively, the silicon raw material 200 is melted in a melt vessel 300 separated from the crucible 210 and at the same time the crucible 210 is heated up to the melting temperature of the silicon and the heating is controlled so that the seeds 220 do not they melt completely. Upon partial melting of the seeds 220, molten raw material 305 can be transferred from the melt container 300 into the crucible 210 and cooling and crystallization can begin. For the
both, consistent with one embodiment of the invention, a portion of the solid body of crystallized silicon can include seeds 220. Alternatively, the seeds can be kept completely solid prior to the introduction of the melt. In this case, the molten silicon in the molten container 300 is heated beyond the melting temperature and the superheated liquid is allowed to melt to a portion of the seed when the superheated liquid is introduced. In a two-stage casting station, such as that shown in Figure 9, the molten raw material 305 can be poured from the melt container 300, land on the seed 220 and acquire its crystallinity during solidification. Alternatively, the melt can be carried out in a central melt container 300 which feeds a distributed distribution of solidification crucibles such as one or more copies of the crucible 210 (not shown). According to the embodiments of the invention, the solidification crucibles can be coated with seeds 220 on either or both sides and at the bottom of the crucibles. Some advantages of this approach include: separation of the melting and solidification systems to allow an optimization of each casting stage; semicontinuous silicon casting, where the melting of new material can be produced in a way
regular, as needed to maintain the supply of the crucible; slag removal from the top (and drained bottom potential) of the silicon while the solidification stations are fed from the middle part of the melt, increasing the purity of the initial silicon material; and by allowing the melt container 300 to equilibrate with molten raw material 305 and no longer be a significant source of impurities. Therefore, after an ingot 260 or 280 has been melted by one of the methods described in the foregoing, the resulting cast ingot can be further processed, for example, by cutting the bottom or other section of the ingot and using it as a single crystal sowing in a subsequent smelting which is carried out to form a monocrystalline silicon body, of almost monocrystalline silicon or of multicrystalline geometric silicon, according to the invention and wherein the size and shape of said single crystal seed is the same size and shape of the bottom of the crucible used in the subsequent casting run and the rest of the ingot can be cut into bricks and plates for processing in photovoltaic cells. Alternatively, the complete ingot can be cut, for example, in horizontal plates for use as seed crystals in multiple casting stations for future castings runs.
The silicon raw material used in the method according to the embodiments of the invention may contain one or more adulterants such as those selected from the list including: boron, aluminum, lithium, gallium, phosphorus, antimony, arsenic and bismuth. The total amount of adulterant can be from approximately 0.01 parts per million atomic percent (ppma) to approximately 2 ppma. Preferably, the amount of adulterant in the silicon is such an amount that the silicon processed plate has a resistivity of from about 0.1 to about 50 ohm-cm, preferably from about 0.5 to about 5.0 ohm-cm. Accordingly, consistent with the present invention, the silicon can be a continuous molten monocrystalline silicon body, molten quasi-monocrystalline silicon or molten continuous geometric multicrystalline silicon that is preferably essentially free, or free of radially distributed defects such as OSF and / or wavy defects and preferably wherein at least two body dimensions are preferably at least about 10 cm and preferably at least about 20 cm, more preferably at least 30 cm, even more preferably so less 40 cm, still more preferably at least 50 cm, still more preferably at least 60 cm and much more
preferable at least about 70 cm. More preferably, the third dimension of the silicon body is at least about 5 cm, preferably at least about 15 cm and more preferably at least about 20 cm. The silicon body can be a separate piece with a single body or it can be contained within or surrounded, totally or partially, by another silicon. The silicon body can be preferably formed with at least two dimensions wherein each is as large as the internal dimensions of the casting container. As described herein, the embodiments of the invention can be used to produce large bodies of monocrystalline silicon, near-monocrystalline silicon or geometric multicrystalline silicon by a simple and cost-effective casting process. The following are examples of experimental results that agree with the embodiments of the invention. These examples are presented to simply exemplify and illustrate embodiments of the invention and should not be considered as limiting the scope of the invention in any way.
Example 1 Preparation of seed: A bolus of pure Czochralski (CZ) silicon (monocrystalline) that is obtained is cut out
from MEMC Inc. and having 0.3 ppma of boron, along its length using a band saw coated with diamond so that it has a square cross section measuring 14 cm per side. The resulting block of monocrystalline silicon is cut through its cross section using the same saw in plates having a thickness of about 2 cm to about 3 cm. These plates are used as seed crystals of monocrystalline silicon or "seeds". The crystallographic pole orientation (100) of the silicon bolus is maintained. The resulting single crystal silicon plates are then distributed at the bottom of a quartz crucible so that the direction (100) of the plates facing upwards and the direction (110) is maintained parallel to one side of the cristol. The quartz crucible has a square cross section with 68 cm on one side, a depth of approximately 40 cm and a wall thickness of approximately 1.8 cm. The plates are distributed in the bottom of the crucible with their long dimensions parallel to the bottom of the crucible and their sides in contact forming a single complete layer of said plates in the bottom of the crucible. Casting: The crucible is filled to a total mass of 265 kg of solid silicon raw material at room temperature. The filled crucible is then loaded into a melt solution by melt / directional solidification in itself that is used to melt
multicrystalline silicon. The melting process is carried out by heating with resistive heaters up to approximately 1550 ° C and the heaters are configured so that the heating comes from the top while allowing the heat to radiate out from the bottom by opening the insulation in a total of 6 cm. This configuration causes the melting to take place in a direction from the top to the bottom, towards the bottom of the crucible. The passive cooling of the bottom caused by the seed crystals that are kept in solid state and at melting temperature, is monitored by a thermocouple. The degree of fusion is measured by a quartz immersion rod that is lowered in the melt every 10 minutes. The height of the dipstick is compared to a measurement taken in an empty crucible at the station to determine the height of the remaining solid material. By measurement by immersion rod, the first melted raw material and then the melting phase is allowed to continue until only a height of about 1.5 cm of the seed crystals remains. At this point, the heating energy is decreased to a temperature set at 1500 ° C while the background radiation is increased by opening the insulation up to 12 cm. One or two additional millimeters of melted seed crystals before solidification begins, as observed by
Immersion rod measurements. The growth of the single sown crystal advances until the end of the solidification stage. The growth stage and the rest of the casting cycle are carried out with the normal parameters where a thermal gradient is uniformed from the top to the bottom and then the entire ingot is cooled slowly to room temperature. The product of molten silicon is an ingot of 66 cm by 66 cm by 24 cm of which a central portion has a horizontal square cross section measuring 50 cm by 50 cm made of monocrystalline silicon from the top to the bottom. The monocrystalline silicon structure is evident from a visual inspection of the ingot surface. Additionally, the etching of silicon with a caustic formula capable of delineating grain boundaries further affirms the lack of grain boundaries in the material. The average bulk adulteration is 1.2 ohms-cm and the photovoltaic cells made of this silicon have an electric efficiency of 16.0%. In other casting tests carried out according to this example it is observed that the molten silicon product is a contiguous glass consisting of silicon containing smaller crystals of silicon or other crystal orientations or is a monocrystalline silicon body having regions adjacent silicon
multicrystalline
EXAMPLE 2 Preparation of seed: Seeding is carried out as in Example 1, except that the monocrystalline silicon seeds are cut so that the direction 110 is 45 degrees on one side of the square seeds for half the seeds while the other half has an angle of approximately 20 degrees. The square pieces are stratified in the bottom of the crucible in the manner of a chessboard alternating two different seed orientations, that is, the direction (110) has an angle of 45 degrees and 20 degrees from the orientation of the sides of the crucible . In relation to each other, the seeds have 25 degrees or 155 degrees of wrong orientation. However, due to the size of the bad pairings of the square-shaped seeds, some separations in the seed layer remain uncovered. The crucible measures approximately 33 cm on each of its square sides and has a height of approximately 22 cm. Casting: The crucible containing the seeds and a separate crucible containing a total of 56 kg of silicon chips as raw material is loaded in a two-stage smelting station of ubiquitous smelting process (UCP). The receiver crucible (with the seeds inside it)
It is heated to the point of silicon melting but the energy is not provided to melt completely. The silicon in the other crucible is melted by resistive graphite heaters at a temperature of at least 50 ° C above the melting temperature of the silicon and then poured into the receiver crucible. At this point, the solidification begins immediately, with heat being extracted from the bottom of the receiver crucible in order to carry out the directional solidification and the growth of seeded crystal. The standard growth cycle is shortened to take into consideration the mass of the solidified material in advance that constitutes the seeds. In this way, instead of allowing the time for all of the 66 kg (10 kg of seeds and 56 kg of raw material silicon) to solidify before the cooling process begins, only time is provided for the 56 kg of molten silicon to avoid wasting heating energy. The product of this process is a silicon ingot with generally large columnar grains having a square cross section and having the shape and dimensions that closely resemble that of the upper surface of the dimensions of the original seed crystal on which they were formed . The positions of lateral grain boundaries are deviated in some cases as growth progresses.
Example 3 Preparation of the seed: The seeding is carried out with 23 kg of square plate (100), used to align the bottom of a crucible that provide a coverage area of 63 cm x 63 cm and a thickness that varies from 3 cm in the center to 1.8 cm on the sides. All plates are distributed with their addresses (110) to 45 ° from the walls of the crucible. Casting: The crucible containing the seeds is filled with an additional total of 242 kg of raw material silicon pieces, representing a mixture of intrinsic silicon, silicon recycled from previous ingots and double cast silicon with a higher p-type resistivity. 9 ohms-cm. The silicon charge in the crucible is loaded onto a one-stage directional solidification furnace. The crucible (with the seeds inside) is heated to a temperature of 1550 ° C while the bottom cools, opening the insulation to 12 cm. The solid-liquid boundary remains substantially flat during casting so that at the end of casting no part of the seed is melted through. The thickness of the silicon is monitored by the use of a quartz immersion rod. When the center thickness is measured at 2.5 cm, the melting stage is stopped, the heater temperature drops to 1140 ° C and the insulation height is increased to15 cm From the start of the solution phase change, the rate of temperature rise is maintained at or below 0.1 ° C / min, measured on the outer surface of the crucible, after reaching the silicon melting temperature elsewhere in the the crucible Then, the remainder of the solidification process is allowed to be carried out with generally constant energy to the heater which is maintained until the end of crystal growth is observed. After completion of growth, the temperature of the crystallized silicon ingot is uniform and then lowered uniformly to room temperature. After separating the ingot from the crucible, the bottom of the ingot is cut into a large piece for later reuse as a seed in another subsequent casting process and the rest of the ingot is cut into 12.5 cm square bricks for further processing. The method is successful in procreating monocrystalline growth substantially over the entire cross-section of the entire seed layer and advancing towards the top of the ingot. The mono-crystallinity is evident from the inspection of the cut silicon. In other foundry tests carried out according to this example it is observed that the molten silicon product is a contiguously concordant crystal of silicon containing smaller crystals of silicon
other crystal orientations or is a monocrystalline silicon body having adjacent regions of multicrystalline silicon. The manufactured silicon plates concordant with the embodiments of the invention are suitably thin and can be used in photovoltaic cells. In addition, the plates can be n-type or p-type. For example, the sheets can have a thickness of approximately 10 micrometers to a thickness of approximately 700 micrometers. In addition, the plates used in the photovoltaic cells preferably have a diffusion length (Lp) that is greater than the thickness of the plate (t). For example, the ratio of Lp to t suitably is at least 0.5. It can be, for example, of at least about 1.1 or at least about 2. The diffusion length is the average distance that minority carriers (such as electrons in p-type material) can diffuse before recombining with most of them. of the carriers (holes in p-type material). The value Lp is related to the duration time of the minority carrier t through the relation Lp = (Dt) 1/2, where D is the diffusion constant. Diffusion length can be measured by numerous techniques such as the induced photon-beam-current technique or the surface photovoltage technique. See, for example, "Fundamentáis of Solar
Cells ", by A. Fahrenbruch and R. Bube, Academic Press, 1983, pp. 90-102, for a description of how the diffusion length can be measured.The plates can have a width of about 100 millimeters to about 600 millimeters Preferably, the sheets have at least one dimension that is at least about 50 mm The processed sheets of the silicon of the invention and consequently the photovoltaic cells made by the invention can have, for example, a surface area of approximately 50 to about 3600 square centimeters The front surface of the plate is preferably textured, For example, the plate can be adequately textured using chemical etching, plasma etching or laser or mechanical writing. pole (100), the plate can be subjected to attack by mordant to form an anisotropic textured surface by treating the plate in an aqueous solution of a base such as sodium hydroxide at an elevated temperature, for example from about 70 ° C to about 90 ° C for about 10 to about 120 minutes. The aqueous solution may contain an alcohol, such as isopropanol. In this way, solar cells can be manufactured
using the produced plates of silicon ingots fused to the embodiments of the invention, by slicing the solid body of molten silicon to form at least one plate, optionally performing a cleaning process on the surface of the plate; optionally perform a texturing step on the surface; form a p-n junction, for example, by adulterating the surface; optionally deposit an antireflective coating on the surface; optionally forming at least one layer that is selected from a back surface field and a passivating layer, for example, by a step of sintering with aluminum and forming electrically conductive contacts on the plate. A passivating layer is a layer that has a boundary with a bare plate surface that joins the free bonds of the surface atoms. Examples of passivating layers on silicon include silicon nitride, silicon dioxide and amorphous silicon. This layer is usually thinner than a micrometer, either transparent to light or acting as an anti-reflective layer. In a typical process in general for preparing photovoltaic cells using, for example, a p-type silicon plate, the plate is exposed on one side to a suitable n-carrier to form a transmitting layer and a pn junction on the front of the receiving side of light
The iron. Typically, the n-type layer of the emitting layer is formed by first depositing the adulterant n on the front surface of the p-type plate using techniques commonly used in the art such as chemical and physical deposition and, after said deposition, the adulterant n, for example phosphorus, is driven into the front surface of the silicon plate for further diffusion of the adulterant n on the surface of the plate. This "activation" stage is commonly carried out by exposing the plate to high temperatures. A p-n junction in this manner is formed in the boundary region between the n-type layer and the p-type silicon plate substrate. The surface of the plate, before the phosphor or other adulterant forms the emitting layer, can be textured. In order to further improve light absorption, an optional anti-reflective coating, such as silicon nitride, can typically be applied to the front of the plate, sometimes providing a simultaneous surface or a bulk passivation. In order to utilize the electrical potential generated by exposure of the pn junction to light energy, the photovoltaic cell is typically provided with a conductive front electrical contact on the front face of the plate and a conductive rear electrical contact on the rear face of the plate. iron, although both contacts can
be on the back of the iron. The contacts are typically made of one or more electrically highly conductive metals and therefore typically are opaque. Therefore, solar cells concordant with the embodiments described in the foregoing may comprise a plate formed of a continuous monocrystalline silicon body or nearly monocrystalline silicon that is free or substantially free of radially distributed defects, the body may be as described in FIG. the above and, for example, having at least two dimensions, each is at least about 25 cm and a third dimension that is at least about 20 cm, a pn junction on the plate, an optional anti-reflective coating on the surface of the iron; which preferably has at least one layer that is selected from a back surface field and a passivating layer; and electrically conductive contacts on the plate, wherein the body may be free or substantially free of wavy and free defects or substantially free of OSF defects. In addition, the solar cells concordant with the embodiments described in the above may comprise a plate formed of a continuous geometric multicrystalline silicon body, the body having a predetermined distribution of grain orientations, preferably with a common pole direction that is perpendicular to a
body surface, the body preferably further has at least two dimensions, each preferably is at least about 10 cm, a pn junction on the plate, an optional anti-reflective coating on a surface of the plate, preferably has at least a layer that is selected from a back surface field and a passivating layer and electrically conductive contacts on the plate, wherein the multicrystalline geometric silicon includes silicon grains having a cross-sectional size of average crystal grain of about 0.5 cm to about 30 cm, and wherein the body may be free or substantially free of wavy defects and free or substantially free of OSF defects. It will be apparent to those skilled in the art that various modifications and variations in the structures and methods described may be made without departing from the scope or spirit of the invention. For example, methods and methods described that relate to the formation of monocrystalline silicon are also applicable to form nearly monocrystalline silicon or multicrystalline silicon combinations thereof. Furthermore, although silicon casting has been described herein, other semiconductor materials and non-metallic crystalline materials can be melted without departing from the scope and spirit of the invention. For example, the inventor
has contemplated the melting of other materials according to the embodiments of the invention such as gallium arsenide, silicon and germanium, aluminum oxide, gallium nitride, zinc oxide, zinc sulphide, gallium and indium arsenide, indium antimonide, germanium, yttrium and barium oxide, lanthanide oxide, magnesium oxide and other semiconductors, oxides and intermetallics with a liquid phase. Other embodiments of the invention will be apparent to those skilled in the art although consideration of the specification and practice of the invention described herein. It is intended that the specification and examples be considered only exemplary where the scope and true spirit of the invention are indicated by the following claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.
Claims (60)
1. A method for manufacturing molten silicon, characterized in that it comprises: placing a geometric distribution of a plurality of silicon seed crystals on at least one surface in the crucible having one or more side walls heated to at least the melting temperature of silicon and at least one wall for cooling; placing the molten silicon in contact with the geometric distribution of seed crystals of monocrystalline silicon; and forming a solid body comprising geometrically ordered multicrystalline silicon, optionally having at least two dimensions, each being at least about 10 cm, by cooling the molten silicon to control crystallization, wherein the shaping includes controlling the solid boundary liquid at an edge of the molten silicon during cooling so that it moves in a direction that increases the distance between the molten silicon and at least one wall for cooling.
2. A method of manufacturing a solar cell, characterized in that it comprises: providing a molten silicon body according to claim 1; forming at least one plate from the body; optionally performing a cleaning procedure on the surface of the plate; optionally perform a texturing step on the surface; form a p-n union; optionally deposit an antireflective coating on the surface; optionally forming at least one layer that is selected from a back surface field and a passivating layer; and forming electrically conductive contacts on the plate.
A method of manufacturing molten silicon, characterized in that it comprises: distributing a plurality of silicon seed crystals in a predetermined pattern on at least two surfaces of a crucible having one or more side walls heated to at least the temperature melting silicon and at least one wall for cooling; placing molten silicon in contact with the plurality of monocrystalline silicon seed crystals; and forming a solid body comprising geometrically ordered multicrystalline silicon, optionally having at least two dimensions, each being at least about 10 cm, by cooling the molten silicon from at least 2 surfaces of the crucible to control crystallization, wherein the shaping includes controlling a solid-liquid boundary on an edge of the molten silicon during cooling so as to move the boundary in a direction that increases a distance between the molten silicon and the monocrystalline silicon seed crystals in the crucible. .
A method of manufacturing molten silicon, characterized in that it comprises: placing a geometric distribution of a plurality of silicon seed crystals on at least one surface in a crucible; placing silicon raw material in contact with the plurality of silicon seed crystals on at least one surface; heating the silicon raw material and the plurality of silicon seed crystals to the melting temperature of the silicon; - - controlling the heating so that the plurality of silicon seed crystals are not completely melted, the control comprises maintaining a T of about 0.1 ° C / min or less, measured on the outer surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible; and once the plurality of seed crystals have partially melted, form a solid body comprising multicrystalline silicon arranged geometrically and by cooling the silicon.
5. A method for manufacturing a solar cell, characterized in that it comprises: providing a molten silicon body according to claim 4; forming at least one plate from the body; optionally performing a cleaning procedure on the surface of the plate; optionally perform a texturing step on the surface; form a p-n union; optionally deposit an antireflective coating on the surface; optionally forming at least one layer that select from a back surface field and a passivating layer; and forming electrically conductive contacts on the plate.
6. A method of manufacturing molten silicon, characterized in that it comprises: distributing a plurality of silicon seed crystals in a predetermined pattern on at least two surfaces of a crucible; placing the silicon raw material in contact with the plurality of silicon seed crystals on at least two of the surfaces; heating the silicon raw material and the plurality of silicon seed crystals to the melting temperature of the silicon; controlling the heating so that the plurality of silicon seed crystals is not completely melted, the control comprises maintaining a T of about 0.1 ° C / min or less, measured on the outer surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible; and once the plurality of seed crystals have been partially melted, forming a solid body comprising multicrystalline silicon arranged geometrically and by cooling of silicon.
7. A method for manufacturing a solar cell, characterized in that it comprises: providing a molten silicon body according to claim 6; forming at least one plate from the body; optionally performing a cleaning procedure on the surface of the plate; optionally perform a texturing step on the surface; form a p-n union; optionally deposit an antireflective coating on the surface; optionally forming at least one layer that is selected from a back surface field and a passivating layer; and forming electrically conductive contacts on the plate.
A method of manufacturing molten silicon, characterized in that it comprises: placing at least one geometric multicrystalline silicon seed crystal on at least one surface in a crucible having one or more side walls heated to at least the temperature of fusion of silicon and at least one wall for cooling; placing molten silicon in contact with at least one seed crystal; and forming a solid body comprising geometrically ordered multicrystalline silicon which optionally has at least two dimensions, each being at least about 10 cm, by cooling the molten silicon to control crystallization, wherein the formation includes controlling a solid boundary. liquid in a molten silicon rim during cooling so that it moves in a direction that increases the distance between the molten silicon and at least one multicrystalline silicon seeding crystal in the crucible.
9. A method of manufacturing a solar cell, characterized in that it comprises: supplying a molten silicon body according to claim 8; forming at least one plate from the body; optionally performing a cleaning procedure on the surface of the plate; optionally perform a texturing step on the surface; form a p-n union; optionally deposit a coating anti-reflective on the surface; optionally forming at least one layer that is selected from a back surface field and a passivating layer; and forming electrically conductive contacts on the plate.
A method of manufacturing molten silicon, characterized in that it comprises: placing a geometric distribution of a plurality of silicon seed crystals on at least one surface in a crucible, the plurality of silicon seed crystals are distributed in a manner that they cover all or substantially one complete area of at least one surface of the crucible; placing molten silicon in contact with the geometric distribution of silicon seed crystals; and forming a solid body comprising geometrically ordered multicrystalline silicon, optionally having at least two dimensions, each being at least about 10 cm, by cooling the molten silicon to control crystallization.
11. A method of manufacturing a solar cell, characterized in that it comprises: supplying a molten silicon body according to claim 8; forming at least one plate from the body; optionally performing a cleaning procedure on the surface of the plate; optionally perform a texturing step on the surface; form a p-n union; optionally deposit an antireflective coating on the surface; optionally forming at least one layer that is selected from a back surface field and a passivating layer; and forming electrically conductive contacts on the plate.
12. A method of manufacturing molten silicon, characterized in that it comprises: placing molten silicon in contact with at least one multicrystalline silicon seeding crystal arranged geometrically in a container having one or more side walls heated to at least the temperature of silicon melting, at least one geometrically arranged multicrystalline silicon seeding crystal distributed to cover all or substantially one complete area of the container surface; and forming a solid body comprising silicon multicrystalline geometrically arranged which optionally has at least two dimensions, each is at least about 10 cm, by cooling the molten silicon to control crystallization.
13. A method of manufacturing a solar cell, characterized in that it comprises: supplying a molten silicon body according to claim 12; forming at least one plate from the body; optionally performing a cleaning procedure on the surface of the plate; optionally perform a texturing step on the surface; form a p-n union; optionally deposit an antireflective coating on the surface; optionally forming at least one layer that is selected from a back surface field and a passivating layer; and forming electrically conductive contacts on the plate.
The method according to any of claims 1, 3, 4, 6, 8, 10 or 12, characterized in that it comprises monitoring the fusion progress using a immersion rod.
15. A solar cell, characterized in that it is manufactured in accordance with the method of any of claims 1, 3, 4, 6, 8, 10 or 12.
16. The method according to any of claims 1, 3, 4 , 6, 8, 10 or 12, characterized in that the cooling includes using a heat dissipating material to radiate heat to water-cooled walls.
The method according to any of claims 1, 3, 4, 6, 8, 10 or 12, characterized in that it comprises forming the body so that it is free or substantially free of free wavy defects or substantially free of fault flaw of oxygen-induced stacking.
18. The method according to any of claims 1, 3, 4, 6, 8, 10 or 12, characterized in that it comprises forming the solid body of multicrystalline silicon arranged geometrically to have at least one dimension that is at least approximately 50 mm.
The method according to any of claims 2, 5, 7, 9, 11 or 13, characterized in that it comprises forming the plate so that it has at least one dimension that is at least about 50 mm.
20. The method according to claim 18, characterized in that it comprises forming the solid body of multicrystalline silicon arranged geometrically so that it is free or substantially free of wavy and free defects or substantially free of oxygen-induced stacking failure defects.
21. The method according to claim 19, characterized in that it comprises forming the plate so that it is free or substantially free of ripple defects and free or substantially free of oxygen-induced stacking failure defects.
22. The method according to any one of claims 1, 3, 4, 6, 10 or 12, characterized in that it comprises forming a portion of the solid body to include the plurality of seed crystals.
23. The method according to claim 8, characterized in that it comprises forming a portion of the solid body to include at least one seed crystal.
24. The method according to any of claims 1, 3 or 10, characterized in that the placement of the molten silicon also includes raw material of molten silicon in a melt container separated from the crucible, heating the crucible and silicon to the temperature of melting of the silicon, controlling the heating so that the plurality of seed crystals in the crucible does not melt completely and transfer the molten silicon from the melting vessel to the crucible.
25. The method according to any of claims 8 to 12, characterized in that the placement of the molten silicon further includes melting silicon raw material in a melt vessel separated from the crucible, heating the crucible and silicon to the melting temperature of the crucible. silicon, control the heating so that at least one seed crystal in the crucible does not melt completely, and transfer the molten silicon from the melt container to the crucible.
26. The method according to any of claims 1, 3, 4, 6 or 10, characterized in that it comprises distributing the plurality of seed crystals so that the common pole direction between the seed crystals is perpendicular to the bottom of the crucible .
The method according to any of claims 1, 3, 4, 6, 8, 10 or 12, characterized in that the formation comprises forming geometrically ordered multicrystalline silicon having an average grain size from about 0.5 cm to about 50 cm so that the direction of common pole is perpendicular to the surface of the multicrystalline silicon ordered geometrically.
28. The method according to any of claims 1, 3, 4, 6, 8 or 10, characterized in that it comprises forming another solid multicrystalline silicon body geometrically ordered using seed glass which is obtained from a previously melt-ordered multicrystalline continuous silicon body, according to the method.
29. The method according to any of claims 1, 3 or 10, characterized in that the placement of the molten silicon further includes heating the crucible and silicon to the melting temperature of the silicon and controlling the heating to maintain a? T of about 0.1 ° C / min or less, measured on the external surface of the crucible, after reaching the melting temperature of the silicon elsewhere in the crucible.
The method according to any of claims 3 or 6, characterized in that it comprises distributing the plurality of seed crystals so that the common pole direction between the seed crystals is perpendicular to one of at least 2 crucible surfaces so that grade limits are not formed between at least two surfaces of the crucible.
31. The method according to any of claims 3 to 6, characterized in that it comprises distributing the plurality of seed crystals so that a maximum of three seed crystal edges coincide in any corner of the predetermined pattern.
32. The method according to any of claims 3 or 6, characterized in that it comprises distributing the predetermined pattern in a hexagonal or octagonal orientation along at least one surface of the crucible.
33. The method according to any of claims 3 or 6, characterized in that at least two surfaces of the crucible are perpendicular.
34. The method according to any of claims 1, 3, 4, 6, 8, 10 or 12, characterized in that it comprises monitoring the progress of the casting using a dip rod or other means.
35. The method according to any of claims 1 or 4, characterized in that the placement of the geometric distribution of a plurality of seed crystals of the monocrystalline silicon comprises distributing the seed crystals to cover all or substantially all of the area of a surface of the crucible.
36. A geometrically continuous multicrystalline ordered silicon body, characterized in that it has a predetermined distribution of grain orientations, the body optionally additionally having at least two dimensions which are each at least about 10 cm and a third dimension of at least approximately 5 cm
37. The body according to claim 36, characterized in that the geometrically ordered multicrystalline silicon includes silicon grains having a cross-sectional size of average crystal grain of about 0.5 cm to about 30 cm.
38. The body according to claim 36, characterized in that the body is free or substantially free of corrugation defects and substantially free of oxygen-induced stacking failure defects.
39. A body of multicrystalline, geometrically ordered, melted, continuous silicon, characterized in that it has a predetermined distribution of grain orientations, the body optionally having at least two dimensions wherein each is at least about 10 cm.
40. The body according to claim 39, characterized in that the geometrically ordered multicrystalline silicon includes silicon grains having a cross-sectional size of average crystal grain of about 0.5 cm to about 50 cm.
41. The body in accordance with claim 39, characterized in that it is free or substantially free of wavy and free defects or substantially free of oxygen-induced stacking failure defects.
42. A geometrically continuous multicrystalline silicon sheet, characterized in that it has a predetermined distribution of grain orientations, the sheet also has at least two dimensions wherein each is at least about 50 mm.
43. The plate according to claim 42, characterized in that it includes silicon grains having a cross-sectional size of average crystal grain of about 0.5 cm to about 50 cm.
44. The plate according to claim 39, characterized in that the plate is free or substantially free of wavy defects and free or substantially free of oxygen-induced stacking failure defects.
45. The body according to any of claims 36 or 39, characterized in that the grain orientations have a common pole direction that is perpendicular to the body surface.
46. The plate according to claim 42, characterized in that the orientations of Grain have a common pole direction that is perpendicular to a surface of the plate.
47. A solar cell, characterized in that it comprises silicon of the silicon body according to any of claims 36 or 39.
48. A solar cell, characterized in that it comprises silicon of the plate according to claim 42.
49. A solar cell , characterized in that it comprises: a plate that is formed from a geometrically continuous multicrystalline silicon body, the body has a predetermined distribution of grain orientations with a common pole direction that is perpendicular to the surface of the body, the body has furthermore at least two dimensions which are each optionally of at least about 10 cm and a third dimension of at least about 5 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the plate; optionally at least one layer that is selected from a back surface field and a passivating layer; and electrically conductive contacts on the griddle .
50. The solar cell according to claim 49, characterized in that the geometrically ordered multicrystalline silicon includes silicon grains having a cross-sectional size of average crystal grain from about 0.5 cm to about 30 cm.
51. The solar cell according to claim 49, characterized in that the body is free or substantially free of wavy defects and free or substantially free of oxygen-induced stacking failure defects.
52. A solar cell, characterized in that it comprises: a plate formed of a multicrystalline silicon body arranged geometrically fused continuously, the body has a predetermined distribution of grain orientations with a common pole direction that is perpendicular to the surface of the body, the body further has at least two dimensions wherein each is optionally at least about 10 cm; a p-n union on the plate; an optional anti-reflective coating on the surface of the plate; optionally at least one layer that select from a back surface field and a passivating layer; and electrically conductive contacts on the plate.
53. The solar cell according to claim 52, characterized in that the geometrically ordered multicrystalline silicon includes silicon grains having a cross-sectional size of average crystal grain from about 0.5 cm to about 30 cm.
54. The solar cell according to claim 52, characterized in that the body is free or substantially free of wavy defects and free or substantially free of oxygen-induced stacking failure defects.
55. A solar cell, characterized in that it comprises: a geometrically continuous multicrystalline silicon sheet having a predetermined distribution of grain orientations with a common pole direction that is perpendicular to the surface of the sheet, the sheet also has at least two dimensions that are each of at least approximately 50 mm; a p-n union on the plate; an optional anti-reflective coating on the surface of the iron; optionally at least one layer that is selected from a back surface field and a passivating layer; and electrically conductive contacts on the plate.
56. The solar cell according to claim 55, characterized in that the geometrically ordered multicrystalline silicon sheet includes silicon grains having a cross-sectional size of average crystal grain of about 0.5 cm to about 30 cm.
57. The solar cell according to claim 55, characterized in that the plate is free or substantially free of wavy defects and free or substantially free of oxygen-induced stacking failure defects.
58. A plate, characterized in that it comprises: silicon formed from a continuously geometrically ordered multicrystalline silicon body, the body has a predetermined distribution of grain orientations with a common pole direction that is perpendicular to a body surface, the body it further has at least two dimensions which are each optionally of at least about 10 cm and a third dimension of at least about 5 cm.
59. A plate, characterized in that it comprises: silicon formed from a multicrystalline silicon body arranged continuously geometrically melted, the body has a predetermined distribution of grain orientations with a common pole direction that is perpendicular to a surface of the body, the The body further has at least two dimensions which are each optionally of at least about 10 cm.
60. A plate, characterized in that it comprises: a geometrically continuous multicrystalline silicon plate having a predetermined distribution of grain orientations with a common pole direction that is perpendicular to a surface of the plate, the plate also has at least two dimensions that are each at least about 50 mm.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60/760,453 | 2006-01-20 | ||
| US60/808,954 | 2006-05-30 | ||
| US60/839,670 | 2006-08-24 | ||
| US60/839,672 | 2006-08-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| MX2008008923A true MX2008008923A (en) | 2008-09-26 |
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