Seed layer structure for crystalline silicon ingot and method for producing crystalline silicon ingot

Abstract

The present invention provides a seed crystal layer structure for crystalline silicon ingot casting and a method for producing crystalline silicon ingots, wherein the seed crystal layer structure comprises a plurality of seed crystal groups, each seed crystal group comprises a plurality of seed crystals arranged in sequence along a first direction, the seed crystals have a top surface and four joint surfaces connected in sequence end to end along a circumferential direction, and the joints between two adjacent seed crystals in the seed crystal group and the joints between two adjacent seed crystals corresponding to the positions in another adjacent seed crystal group are staggered. When the seed crystal layer structure is used to produce crystalline silicon ingots, the joints between adjacent seed crystals can form stable three-pronged grain boundaries during the ingot casting process, reduce dislocation proliferation, and reduce defect density.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic manufacturing, and in particular to a seed layer structure for crystalline silicon ingots and a production method of crystalline silicon ingots. Background Art

[0002] Since the end of the last century, with the crisis of traditional fossil energy and people's attention to clean energy, the photovoltaic industry has achieved vigorous development. Among them, crystalline silicon cells and photovoltaic modules still occupy an important position in the entire photovoltaic market. Compared with single crystal silicon rods produced by the Czochralski method, crystalline silicon ingots produced by directional solidification casting have better cost performance, but how to reduce the defect density of the above crystalline silicon ingots has been a topic that manufacturers have been focusing on.

[0003] The industry has disclosed a technical solution to improve crystalline silicon ingot casting by controlling the temperature gradient and the temperature field in the crucible; at the same time, there is also a solution to adjust the seed crystal morphology and crystal orientation for ingot casting. However, most of the above solutions place the seed crystals at the bottom of the crucible in a cross-stitching manner, which results in unstable cross grain boundaries. The crystal growth process is affected by interfacial tension, crystal growth and annealing stress, resulting in the proliferation of dislocations and increased defects.

[0004] Therefore, it is necessary to provide a new seed layer structure for crystalline silicon ingots and a method for producing crystalline silicon ingots. Summary of the invention

[0005] The object of the present invention is to provide a seed layer structure for crystalline silicon ingot and a method for producing a crystalline silicon ingot, which can reduce dislocation and defect density and improve the quality of the crystalline silicon ingot.

[0006] To achieve the above-mentioned purpose of the invention, the present invention provides a seed layer structure for crystalline silicon ingots, including a plurality of seed crystal groups, each seed crystal group including a plurality of seed crystals arranged in sequence along a first direction, the seed crystal having a top surface and four splicing surfaces connected in sequence end to end along a circumferential direction, and the joint between two adjacent seed crystals in the seed crystal group is staggered with the joint between two adjacent seed crystals in corresponding positions in another adjacent seed crystal group.

[0007] As a further improvement of the present invention, the seed crystal includes a first seed crystal, a second seed crystal and a third seed crystal obtained by cutting along different crystal planes on a single crystal silicon rod.

[0008] As a further improvement of the present invention, the top surfaces of the first seed crystal, the second seed crystal and the third seed crystal are all {100} crystal planes.

[0009] As a further improvement of the present invention, the four edges of the first seed crystal are spliced ​​with at most six seed crystals, and the six seed crystals include three second seed crystals and three third seed crystals.

[0010] As a further improvement of the present invention, the first seed crystal, the second seed crystal and the third seed crystal in each seed crystal group are arranged in sequence.

[0011] As a further improvement of the present invention, the first seed crystal, the second seed crystal and the third seed crystal have the same appearance and are all arranged in a flat square shape.

[0012] As a further improvement of the present invention, edge seed crystals are further provided at the head end or the tail end of the seed crystal group, so that the two ends of adjacent seed crystal groups are flush.

[0013] As a further improvement of the present invention, the edge seed crystal is obtained by cutting the first seed crystal or the second seed crystal or the third seed crystal, and the top surface area of ​​the edge seed crystal is smaller than the top surface areas of the first seed crystal, the second seed crystal and the third seed crystal.

[0014] As a further improvement of the present invention, there is only one edge seed crystal in each seed crystal group, and in any two adjacent seed crystal groups, the edge seed crystal in one seed crystal group is located at the head end of the seed crystal group, while the edge seed crystal in the other seed crystal group is located at the end of the seed crystal group.

[0015] As a further improvement of the present invention, the misalignment length of the joints between two adjacent seed crystals in the seed crystal group and the joints between two corresponding adjacent seed crystals in another adjacent seed crystal group along the first direction is not less than 5 mm.

[0016] The present invention also provides a method for producing a crystalline silicon ingot, which mainly comprises:

[0017] Cutting to obtain a plurality of seed crystals, wherein the seed crystals have a top surface and four splicing surfaces which are sequentially connected end to end along a circumferential direction;

[0018] Selecting a number of seed crystals and arranging them in sequence along a first direction to obtain a seed crystal group, and then arranging the number of seed crystal groups along a second direction perpendicular to the first direction to obtain a seed crystal layer structure, so that the seams between two adjacent seed crystals in any seed crystal group are staggered with the seams between two corresponding seed crystals in another adjacent seed crystal group;

[0019] The silicon material is placed on the seed crystal layer structure, heated until the silicon material is melted, and then directionally solidified to obtain the corresponding crystalline silicon ingot.

[0020] As a further improvement of the present invention, the plurality of seed crystals are obtained by cutting from the same single crystal silicon rod; or, the plurality of seed crystals are obtained by cutting from at least two single crystal silicon rods.

[0021] As a further improvement of the present invention, the “cutting to obtain a plurality of seed crystals” includes: cutting a single crystal silicon rod along a predetermined direction to obtain a first seed crystal;

[0022] The single crystal silicon rod is rotated by a first deflection angle, and then cut along the same direction to obtain a second seed crystal;

[0023] The single crystal silicon rod is rotated to a second deflection angle and then cut along the same direction to obtain a third seed crystal.

[0024] As a further improvement of the present invention, it specifically includes:

[0025] Select <100> A single crystal silicon rod having a crystalline direction is cut along a {100} crystal plane to obtain a first seed crystal;

[0026] The single crystal silicon rod is rotated clockwise along its axial direction by a first deflection angle to cut and obtain a second seed crystal.

[0027] As a further improvement of the present invention, the first deflection angle and the second deflection angle are consistent in magnitude and opposite in direction.

[0028] As a further improvement of the present invention, both the first deflection angle and the second deflection angle are set to 25-35°.

[0029] As a further improvement of the present invention, the first seed crystal, the second seed crystal and the third seed crystal in the seed crystal group are arranged in sequence along the first direction, and any two first seed crystals, two second seed crystals and two third seed crystals in the seed crystal layer structure are not in contact with each other.

[0030] As a further improvement of the present invention, the “cutting to obtain a plurality of seed crystals” further includes: cutting to obtain edge seed crystals, and then arranging the edge seed crystals at one end of the seed crystal group so that the two ends of adjacent seed crystal groups are flush.

[0031] As a further improvement of the present invention, the edge seed crystal is obtained by cutting the first seed crystal or the second seed crystal or the third seed crystal along a second direction perpendicular to the first direction.

[0032] As a further improvement of the present invention, the misalignment length of the joints between two adjacent seed crystals in the seed crystal group and the joints between two corresponding adjacent seed crystals in another adjacent seed crystal group along the first direction is not less than 5 mm.

[0033] The beneficial effects of the present invention are: by adopting the seed crystal layer structure and the production method of the crystalline silicon ingot of the present invention, by staggering the seed crystals of different seed crystal groups to form a T-shaped joint, a stable three-pronged grain boundary can be formed during the growth of the crystalline silicon ingot, thereby reducing the dislocation and defect density and improving the quality of the crystalline silicon ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic plan view of a preferred embodiment of the seed layer structure of the present invention;

[0035] Figure 2 Schematic diagram of the crystal orientation structure of the first seed crystal in the seed crystal layer structure of the present invention;

[0036] Figure 3 Schematic diagram of the cutting direction of the second seed crystal in the seed crystal layer structure of the present invention;

[0037] Figure 4 It is a schematic diagram of the main process of the production method of crystalline silicon ingot of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below in conjunction with the embodiments shown in the accompanying drawings. However, the embodiments do not limit the present invention, and any structural, methodological, or functional changes made by a person skilled in the art based on the embodiments are all within the protection scope of the present invention.

[0039] Ginseng Figures 1 to 3 As shown, the seed crystal layer structure 100 for crystalline silicon ingot provided by the present invention comprises a plurality of seed crystal groups 10, each of which comprises a plurality of seed crystals arranged in sequence along a first direction. The seed crystal has a top surface and four splicing surfaces connected in sequence end to end along a circumferential direction, and the top surfaces of the plurality of seed crystals belong to the same crystal plane.

[0040] The joints of two adjacent seed crystals in the seed crystal group 10 are staggered with the joints of two corresponding adjacent seed crystals in another adjacent seed crystal group 10, that is, different seed crystals in adjacent seed crystal groups form a T-shaped joint. The length of the joints of two adjacent seed crystals in the seed crystal group 10 and the joints of two corresponding adjacent seed crystals in another adjacent seed crystal group 10 along the first direction is not less than 5 mm. In the subsequent crystal growth process, the corresponding T-shaped grain boundaries gradually form stable three-pronged grain boundaries under the action of interfacial tension, which can effectively reduce dislocation proliferation and defects compared to traditional cross grain boundaries.

[0041] In this embodiment, the seed crystal group 10 includes a first seed crystal A, a second seed crystal B and a third seed crystal C arranged in sequence, and the first seed crystal A, the second seed crystal B and the third seed crystal C have the same appearance so as to be closely spliced ​​with each other. The first seed crystal A, the second seed crystal B and the third seed crystal C are obtained by cutting the corresponding single crystal silicon rod along different crystal planes, specifically, the splicing surfaces of the first seed crystal A, the second seed crystal B and the third seed crystal C are cut along different crystal planes. Here, the top surfaces of the first seed crystal A, the second seed crystal B and the third seed crystal C are all {100} crystal planes.

[0042] Any two first seed crystals A, two second seed crystals B, and two third seed crystals C are arranged at intervals from each other in the horizontal direction, that is, seed crystals of the same type do not touch each other. Taking the first seed crystal A as an example, the edges of the first seed crystal A are spliced ​​with at most six seed crystals, and the six seed crystals include three second seed crystals B and three third seed crystals C. The first seed crystal A is connected to the second seed crystal B and the third seed crystal C respectively along the first direction, and the first seed crystal A is also only connected to the second seed crystal B and / or the third seed crystal C in the second direction. The first seed crystals A are not in direct contact with each other, avoiding dislocation caused by phase difference.

[0043] The crystal plane where the splicing surface of the second seed crystal B is located has a first angle with the crystal plane where the splicing surface of the first seed crystal A is located on the same side, and the crystal plane where the splicing surface of the third seed crystal C is located has a second angle with the crystal plane where the splicing surface of the first seed crystal A is located on the same side. Wherein, both the first angle and the second angle are set to 25-35°, so that the splicing position of the first seed crystal A and the second seed crystal B, and the first seed crystal A and the third seed crystal C can form a grain boundary with low energy state density. Here, the first angle and the second angle are of the same size and opposite direction. In other words, the second seed crystal B and the third seed crystal C are symmetrical in crystal direction, and a large-angle random grain boundary is formed at the corresponding position of the joint between the two, thereby reducing the defect density of the crystalline silicon ingot obtained by subsequent ingot casting.

[0044] The first seed crystal A, the second seed crystal B and the third seed crystal C are all arranged in a flat block shape, and their length and width in the horizontal direction are consistent, and their width is mostly set to about 20 mm. Usually, the first seed crystal A, the second seed crystal B and the third seed crystal C can be obtained by cutting the corresponding single crystal silicon rod, and their long crystal faces are mostly crystal faces perpendicular to the axial direction of the single crystal silicon rod. The length and width of the above seed crystals in the horizontal direction are preferably adapted to the size of the single crystal silicon rod to reduce silicon material waste.

[0045] In this embodiment, the top surfaces of the first seed crystal A, the second seed crystal B and the third seed crystal C are all {100} crystal planes, and the top surfaces of the first seed crystal A, the second seed crystal B and the third seed crystal C are set to 157 mm*157 mm.

[0046] The seed crystal layer structure 100 further includes an edge seed crystal D disposed at one end of the seed crystal group 10, through which the two ends of the adjacent seed crystal group 10 are flush, thereby making the seed crystal layer structure 100 rectangular as a whole. Of course, the thickness of the edge seed crystal D is consistent with the aforementioned first seed crystal A, second seed crystal B and third seed crystal C, and its length in the first direction can be determined according to the overall size specification of the seed crystal layer structure 100.

[0047] The edge seed crystal D can be obtained by simply cutting the first seed crystal A or the second seed crystal B or the third seed crystal C, that is, the crystal plane where the splicing surface of the edge seed crystal D is located is consistent with the crystal plane where the splicing surface of the first seed crystal A or the second seed crystal B or the third seed crystal C is located. The edge seed crystal D corresponding to the end of the seed crystal group 10 is also not in contact with the same seed crystal. If the crystal plane of the edge seed crystal D is consistent with the first seed crystal A, that is, when the edge seed crystal D is cut from the first seed crystal A, the edge seed crystal is recorded as D(A), which does not directly cooperate with the first seed crystal A. Here, the size of the edge seed crystal D along the horizontal direction is set to 157mm*147mm, that is, the offset length of the joint between two adjacent seed crystals in the seed crystal group 10 and the joint between the corresponding two seed crystals in another adjacent seed crystal group 10 is 10mm.

[0048] The specific size and style of the seed crystal layer structure 100 can be determined according to the corresponding ingot crucible. In actual operation, at least part of the seed crystals located on the peripheral side of the seed crystal layer structure 100 can be cut to meet production requirements, which will not be repeated here.

[0049] Ginseng Figure 4 As shown, the present invention also provides a method for producing a crystalline silicon ingot, which mainly comprises:

[0050] Cutting to obtain a plurality of seed crystals, wherein the seed crystals have a top surface and four splicing surfaces which are sequentially connected end to end along a circumferential direction;

[0051] A plurality of seed crystals are selected and arranged in sequence along a first direction to obtain a seed crystal group 10, and then the plurality of seed crystal groups 10 are arranged along a second direction perpendicular to the first direction to obtain the aforementioned seed crystal layer structure 100, wherein the seed crystal layer structure 100 matches the shape of the corresponding crucible bottom, and the joints of two adjacent seed crystals in any seed crystal group 10 are staggered with the joints of two adjacent seed crystals in another adjacent seed crystal group 10;

[0052] The silicon material is placed on the seed crystal layer structure 100, heated until the silicon material is melted, and then directionally solidified to obtain the corresponding crystalline silicon ingot.

[0053] The seed crystal cutting process includes:

[0054] A single crystal silicon rod is selected, and a first seed crystal A is obtained by cutting the single crystal silicon rod along a predetermined direction;

[0055] The single crystal silicon rod is rotated along the top surface normal of the first seed crystal A by a first deflection angle α, and then cut along the same direction to obtain a second seed crystal B;

[0056] The single crystal silicon rod is rotated along the top surface normal of the first seed crystal A by a second deflection angle α', and then cut along the same direction to obtain a third seed crystal C.

[0057] In this embodiment, the above-mentioned cutting process includes selecting <100> A single crystal silicon rod with a crystal orientation is cut along the {100} crystal plane to obtain a first seed crystal A; the single crystal silicon rod is then rotated along its axial direction by a first deflection angle α, and then cut along the same direction to obtain a second seed crystal B, that is, the first angle between the crystal plane where the splicing plane of the second seed crystal B is located and the crystal plane where the splicing plane on the same side of the first seed crystal A is located is the first deflection angle α. Similarly, the single crystal silicon rod is rotated along its axial direction by a second deflection angle α', and then cut along the same direction to obtain a third seed crystal C, and the second angle between the crystal plane where the splicing plane of the third seed crystal C is located and the crystal plane where the splicing plane on the same side of the first seed crystal A is located is the second deflection angle α'. In particular, both the first deflection angle α and the second deflection angle α' are set to 25-35°, and their sizes are consistent and the directions are opposite.

[0058] Obviously, the first seed crystal A, the second seed crystal B, and the third seed crystal C can be cut from the same single crystal silicon rod or cut from different single crystal silicon rods. In another embodiment of the present invention, the cutting process includes:

[0059] Selecting a first single crystal silicon rod and cutting it along a predetermined crystal plane to obtain a first seed crystal A;

[0060] A second single crystal silicon rod is selected and cut to obtain a second seed crystal B, wherein the angle between the crystal plane where the splicing surface of the second seed crystal B is located and the crystal plane where the splicing surface on the same side of the first seed crystal is located is set to 25-35°.

[0061] In addition, in order to make the edge of the seed crystal layer structure 100 fit closely with the corresponding crucible, the production method further includes cutting the edge seed crystal D, and then setting the edge seed crystal D at one end of the seed crystal group 10, so that the two ends of the adjacent seed crystal groups 10 are flush. The specific arrangement method of the seed crystal layer structure 100 is as follows: firstly, the first seed crystal A, the second seed crystal B, the third seed crystal C and the edge seed crystal D are arranged along a first direction to obtain a seed crystal group 10, and then several seed crystal groups 10 are arranged closely along a second direction perpendicular to the first direction.

[0062] The edge seed crystal D is obtained by cutting the first seed crystal A or the second seed crystal B or the third seed crystal C along the second direction, that is, the top surface of the edge seed crystal D is also a {100} crystal plane, and the crystal plane where the splicing surface of the edge seed crystal D is located is consistent with the crystal plane where the splicing surface of the first seed crystal A or the second seed crystal B or the third seed crystal C is located. The dislocation length along the first direction between the joint of two adjacent seed crystals in the seed crystal group 10 and the joint of adjacent seed crystals in another adjacent seed crystal group 10 is not less than 5mm. The dislocation length is equivalent to the difference between the length of the edge seed crystal D and the first seed crystal A or the second seed crystal B or the third seed crystal C along the first direction.

[0063] In summary, by adopting the seed crystal layer structure 100 and the method for producing a crystalline silicon ingot of the present invention, by arranging different seed crystals to form a T-shaped joint, a stable three-pronged grain boundary can be formed during the casting process, while reducing the dislocation and defect density; and, the adjacent splicing positions of the first seed crystal A and the second seed crystal B, and the first seed crystal and the third seed crystal C can form a grain boundary with a low energy state density, which can also reduce the internal dislocations and defects of the crystalline silicon ingot and improve the quality of the crystalline silicon ingot.

[0064] It should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0065] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A seed crystal layer structure for crystalline silicon ingot, comprising a plurality of seed crystal groups, each seed crystal group comprising a plurality of seed crystals arranged in sequence along a first direction, the seed crystals having a top surface and four splicing surfaces connected in sequence end to end along a circumferential direction, characterized in that: The joints between two adjacent seed crystals in the seed crystal group are staggered with the joints between two adjacent seed crystals in the other adjacent seed crystal group that have the same position; the seed crystals include a first seed crystal, a second seed crystal and a third seed crystal obtained by cutting along different crystal planes on a single crystal silicon rod, and any two first seed crystals, two second seed crystals and two third seed crystals are spaced apart from each other in the horizontal direction.

2. The seed layer structure according to claim 1, characterized in that: The top surfaces of the first seed crystal, the second seed crystal and the third seed crystal are all {100} crystal planes.

3. The seed layer structure according to claim 1, characterized in that: The four edges of the first seed crystal are spliced ​​with six seed crystals at most, and the six seed crystals include three second seed crystals and three third seed crystals.

4. The seed layer structure according to claim 1, characterized in that: The first seed crystal, the second seed crystal and the third seed crystal in each seed crystal group are arranged in sequence.

5. The seed layer structure according to claim 1, characterized in that: The first seed crystal, the second seed crystal and the third seed crystal have the same appearance and are all arranged in a flat square shape.

6. The seed layer structure according to claim 5, characterized in that: The beginning or the end of the seed crystal group is also provided with an edge seed crystal, so that the two ends of the adjacent seed crystal groups are flush.

7. The seed layer structure according to claim 6, characterized in that: The edge seed crystal is obtained by cutting the first seed crystal, the second seed crystal or the third seed crystal, and the top surface area of ​​the edge seed crystal is smaller than the top surface areas of the first seed crystal, the second seed crystal and the third seed crystal.

8. The seed layer structure according to claim 6, characterized in that: Each seed crystal group has only one edge seed crystal, and in any two adjacent seed crystal groups, the edge seed crystals in one seed crystal group are located at the head end of the seed crystal group, while the edge seed crystals in the other seed crystal group are located at the end of the seed crystal group.

9. The seed layer structure according to claim 1, characterized in that: The misalignment length of the joints between two adjacent seed crystals in the seed crystal group and the joints between two corresponding adjacent seed crystals in another adjacent seed crystal group along the first direction is not less than 5 mm.

10. A method for producing a crystalline silicon ingot, characterized in that: Cutting to obtain a plurality of seed crystals, wherein the seed crystals have a top surface and four splicing surfaces that are sequentially connected end to end along a circumferential direction, and the seed crystals include a first seed crystal, a second seed crystal, and a third seed crystal that are cut along different crystal planes on a single crystal silicon rod; Selecting a number of seed crystals and arranging them in sequence along a first direction to obtain a seed crystal group, and then arranging the number of seed crystal groups along a second direction perpendicular to the first direction to obtain a seed crystal layer structure, so that the joints between two adjacent seed crystals in any seed crystal group are staggered with the joints between two corresponding seed crystals in another adjacent seed crystal group, and any two first seed crystals, two second seed crystals, and two third seed crystals are spaced apart from each other in the horizontal direction; The silicon material is placed on the seed crystal layer structure, heated until the silicon material is melted, and then directionally solidified to obtain the corresponding crystalline silicon ingot.

11. The production method according to claim 10, characterized in that: The plurality of seed crystals are obtained by cutting from the same single crystal silicon rod; or, the plurality of seed crystals are obtained by cutting from at least two single crystal silicon rods.

12. The production method according to claim 10, characterized in that: Cutting the single crystal silicon rod along a predetermined direction to obtain a first seed crystal; The single crystal silicon rod is rotated by a first deflection angle, and then cut along the same direction to obtain a second seed crystal; The single crystal silicon rod is rotated to a second deflection angle and then cut along the same direction to obtain a third seed crystal.

13. The production method according to claim 12, characterized in that: Select <100> A single crystal silicon rod having a crystalline direction is cut along a {100} crystal plane to obtain a first seed crystal; The single crystal silicon rod is rotated clockwise along its axial direction by a first deflection angle to cut and obtain a second seed crystal.

14. The production method according to claim 12, characterized in that: The first deflection angle and the second deflection angle are consistent in magnitude and opposite in direction.

15. The production method according to claim 12, characterized in that: The first deflection angle and the second deflection angle are both set to 25-35 degrees.

16. The production method according to claim 12, characterized in that: The first seed crystal, the second seed crystal and the third seed crystal in the seed crystal group are arranged in sequence along the first direction.

17. The production method according to claim 12, characterized in that: The “cutting to obtain a plurality of seed crystals” also includes: cutting to obtain edge seed crystals, and then arranging the edge seed crystals at one end of the seed crystal group so that the two ends of adjacent seed crystal groups are flush.

18. The production method according to claim 17, characterized in that: The edge seed crystal is obtained by cutting the first seed crystal, the second seed crystal or the third seed crystal along a second direction perpendicular to the first direction.

19. The production method according to claim 10, characterized in that: The misalignment length of the joints between two adjacent seed crystals in the seed crystal group and the joints between two corresponding adjacent seed crystals in another adjacent seed crystal group along the first direction is not less than 5 mm.

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