Methods and Apparatuses for Manufacturing Monocrystalline Cast Silicon and Monocrystalline Cast Silicon Bodies for Photovoltaics

Abstract

Methods and apparatuses are provided for casting silicon for photovoltaic cells and other applications. With such methods and apparatuses, a cast body of monocrystalline silicon may be formed that is free of, or substantially free of, radially-distributed impurities and defects and having at least two dimensions that are each at least about 35 cm is provided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the features, advantages, and principles of the invention. In the drawings:

FIG. 1 illustrates an exemplary arrangement of silicon seeds on the bottom surface of a crucible, according to an embodiment of the present invention;

FIG. 2 illustrates another exemplary arrangement of silicon seeds on the bottom and side surfaces of a crucible, according to an embodiment of the present invention;

FIG. 3A-3C illustrate an example of tiling for casting geometrically ordered multi-crystalline silicon in a crucible, according to an embodiment of the present invention;

FIG. 4 illustrates another example of tiling for casting geometrically ordered multi-crystalline silicon in a crucible, according to an embodiment of the present invention;

FIG. 5 illustrates an example of a close-packed array of hexagon seed tiles, according to an embodiment of the present invention;

FIG. 6 illustrates an exemplary array of polygonal shapes having rhomboid or triangular interstices, according to an embodiment of the present invention

FIG. 7 illustrates an exemplary method, according to an embodiment of the present invention; and

FIGS. 8A-8G and 9 illustrate exemplary casting processes for monocrystalline or geometrically ordered multi-crystalline silicon, according to embodiments of the present invention.

Claims

1. A method of manufacturing cast silicon, comprising: placing molten silicon in contact with at least one silicon seed crystal in a vessel having one or more side walls heated to at least the melting temperature of silicon and at least one wall for cooling; andforming a solid body comprising monocrystalline silicon, optionally having at least two dimensions each being at least about 10 cm, by cooling the molten silicon to control crystallization, wherein the forming includes forming a solid-liquid interface at an edge of the molten silicon that at least initially parallels the at least one wall for cooling, the interface being controlled during the cooling so as to move in a direction that increases a distance between the molten silicon and the at least one wall for cooling.

2. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 1;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

3. The method according to claims 1 or 2, wherein the placing further includes placing the at least one silicon seed crystal in a bottom of a crucible, andfurther wherein the cooling moves the solid-liquid interface in a direction away from the bottom of the crucible while maintaining the edge that parallels the at least one wall for cooling.

4. The method according to claim 3, further comprising arranging the at least one seed crystal so that a specific pole direction is perpendicular to a bottom of the crucible.

5. The method according to claim 3, wherein the placing molten silicon further includes melting silicon feedstock in a melt container separate from the crucible, heating the crucible and the silicon to the melting temperature of silicon, controlling the heating so that the at least one seed crystal in the crucible does not melt completely, and transferring the molten silicon from the melt container into the crucible.

6. The method according to claim 3, further including forming a portion of the body to include the at least one seed crystal.

7. A method of manufacturing cast silicon, comprising: placing a geometric arrangement of a plurality of silicon seed crystals comprising monocrystalline silicon on at least one surface in a crucible having one or more side walls heated to at least the melting temperature of silicon and at least one wall for cooling, wherein the geometric arrangement includes close-packed polygons;placing molten silicon in contact with the geometric arrangement of the silicon seed crystals; andforming a solid body comprising monocrystalline silicon, optionally having at least two dimensions each being at least about 10 cm, by cooling the molten silicon to control crystallization, wherein the forming includes forming a solid-liquid interface at an edge of the molten silicon that parallels the at least one wall for cooling, the interface being controlled during the cooling so as to move in a direction that increases a distance between the molten silicon and the at least one wall for cooling.

8. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 7;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

9. A method of manufacturing cast silicon, comprising: arranging a plurality of silicon seed crystals comprising monocrystalline silicon in a predetermined pattern on at least two surfaces of a crucible;placing molten silicon in contact with the monocrystalline silicon seed crystals; andforming a solid body comprising monocrystalline silicon, optionally having at least two dimensions each being at least about 10 cm, by cooling the molten silicon from the at least two surfaces of the crucible to control crystallization, wherein the forming includes controlling a solid-liquid interface at an edge of the molten silicon during the cooling so as to move in a direction that increases a distance between the molten silicon and the at least two surfaces of the crucible.

10. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 9;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

11. A method of manufacturing cast silicon, comprising: placing silicon feedstock in contact with at least one silicon seed crystal comprising monocrystalline silicon on at least one surface;heating the silicon feedstock and the at least one silicon seed crystal to the melting temperature of silicon;controlling the heating so that the at least one silicon seed crystal does not melt completely, the controlling comprising maintaining a ΔT of about 0.1° C./min or less, as measured on an outside surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible; and, once the at least one silicon seed crystal is partially melted,forming a solid body comprising monocrystalline silicon by cooling the silicon.

12. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 11;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

13. The method according to claims 9 or 11, wherein the placing further includes placing the at least one silicon seed crystal in a bottom of a crucible.

14. The method according to claims 9 or 11, further including forming a portion of the body to include the at least one seed crystal.

15. A method of manufacturing cast silicon, comprising: placing a geometric arrangement of a plurality of silicon seed crystals comprising monocrystalline silicon on at least one surface in a crucible, wherein the geometric arrangement includes close-packed polygons;placing silicon feedstock in contact with the plurality of silicon seed crystals on the at least one surface;heating the silicon feedstock and the plurality of silicon seed crystals to the melting temperature of silicon;controlling the heating so that the plurality of seed crystals does not melt completely, the controlling comprising maintaining a ΔT of about 0.1° C./min or less, as measured on an outside surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible; and, once the at least one silicon seed crystal is partially melted,forming a solid body comprising monocrystalline silicon by cooling the silicon.

16. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 15;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

17. A method of manufacturing cast silicon, comprising: arranging a plurality of silicon seed crystals comprising monocrystalline silicon in a predetermined pattern on at least two surfaces of a crucible;placing silicon feedstock in contact with the plurality of silicon seed crystals on the at least two surfaces;heating the silicon feedstock and the plurality of silicon seed crystals to the melting temperature of silicon;controlling the heating so that the plurality of silicon seed crystals does not melt completely, the controlling comprising maintaining a ΔT of about 0.1° C./min or less, as measured on an outside surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible; and, once at least one monocrystalline silicon seed crystal is partially melted,forming a solid body comprising monocrystalline silicon by cooling the silicon.

18. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 17;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

19. A method of manufacturing cast silicon, comprising: placing molten silicon in contact with at least one silicon seed crystal in a vessel having one or more side walls heated to at least the melting temperature of silicon, the at least one silicon seed crystal arranged to cover an entire or substantially an entire area of a surface of the vessel; andforming a solid body comprising monocrystalline silicon, optionally having at least two dimensions each being at least about 10 cm, by cooling the molten silicon to control crystallization.

20. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 19;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

21. A solar cell, manufactured according to the method of claims 1, 7, 9, 11, 15, 17, or 19.

22. The method according to claims 1, 3, 7-12, or 15-19, wherein the cooling includes using a heat sink material for radiating heat to water-cooled walls.

23. The method according to claims 1, 3, 7-12, or 15-19, further comprising forming the body to be substantially free of swirl defects and substantially free of oxygen-induced stacking fault defects.

24. The method according to claims 1, 7, 9, 11, 15, 17, or 19, further comprising forming a wafer having at least one dimension being at least about 50 mm.

25. The method according to claims 2, 8, 10, 12, 16, 18, or 20, further comprising forming the wafer to have at least one dimension be at least about 50 mm.

26. The method according to claim 24, further comprising forming the wafer to be substantially free of swirl defects and substantially free of oxygen-induced stacking fault defects.

27. The method according to claim 25, further comprising forming the wafer to be substantially free of swirl defects and substantially free of oxygen-induced stacking fault defects.

28. The method according to claims 7-12 or 15-18, further including forming a portion of the body to include the plurality of seed crystals.

29. The method according to any one of claims 7-10 and 15-18, wherein the placing molten silicon further includes melting silicon feedstock in a melt container separate from the crucible, heating the crucible and the silicon to the melting temperature of silicon, controlling the heating so that the plurality of seed crystals in the crucible does not melt completely, and transferring the molten silicon from the melt container into the crucible.

30. The method according to any one of claims 1, 2, 11, 12, 19, and 20, wherein the placing molten silicon further includes melting silicon feedstock in a melt container separate from the crucible, heating the crucible and the silicon to the melting temperature of silicon, controlling the heating so that the at least one seed crystal in the crucible does not melt completely, and transferring the molten silicon from the melt container into the crucible.

31. The method according to any one of claims 7, 8, 15, or 16, further comprising arranging the plurality of seed crystals so that a common pole direction among the seed crystals is perpendicular to a bottom of the crucible.

32. The method according to any one of claims 1, 3, 7-12 or 15-20, further comprising forming another solid body of silicon using a seed crystal cut from a body of silicon previously cast according to said method.

33. The method according to any one of claims 7-10, wherein the placing molten silicon further includes heating the crucible and the silicon to the melting temperature of silicon, and controlling the heating to maintain a ΔT of about 0.1° C./min or less, as measured on an outside surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible.

34. The method according to any one of claims 1, 2, 19, and 20, wherein the placing molten silicon further includes heating the crucible and the silicon to the melting temperature of silicon, and controlling the heating to maintain a ΔT of about 0.1° C./min or less, as measured on an outside surface of the crucible, after reaching the melting temperature of silicon elsewhere in the crucible.

35. The method according to any one of claims 9, 11, or 18, further comprising arranging the plurality of seed crystals so that a common pole direction among the seed crystals is perpendicular to one of the at least two surfaces of the crucible so that no grain boundaries are formed between the at least two surfaces of the crucible.

36. The method according to any one of claims 9, 11, or 18, further comprising arranging the plurality of seed crystals so that a maximum of six seed crystal edges meet at any corner of the predetermined pattern.

37. The method according to any one of claims 9, 11, 17, or 18, further comprising arranging the predetermined pattern in a hexagonal or octagonal orientation along the at least one surface of the crucible.

38. The method according to any one of claims 9, 11, 17, or 18, wherein the at least two surfaces of the crucible are perpendicular.

39. The method according to any one of claims 1, 7, 9, 11, 15, 17, or 19, further comprising monitoring a progress of melting by using a dip rod.

40. The method according to any one of claims 1, 7, 9, 11, 15, 17, or 19, wherein the forming comprises forming a solid body of monocrystalline silicon or near-monocrystalline silicon.

41. The method according to claim 1, wherein the placing includes arranging the at least one silicon seed crystal to cover an entire or substantially an entire area of a surface of the vessel.

42. A body of continuous monocrystalline silicon being free or substantially free of radially-distributed impurities and defects, and having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

43. A body of continuous monocrystalline silicon having a carbon concentration of about 2×1016 atoms/cm3 to about 5×1017 atoms/cm3, an oxygen concentration not exceeding 5×1017 atoms/cm3, a nitrogen concentration of at least 1×1015 atoms/cm3, and having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

44. The body according to claim 42, wherein the body is free or substantially free of swirl defects and substantially free of oxygen-induced stacking fault defects.

45. A body of continuous cast monocrystalline silicon having at least two dimensions that are each at least about 35 cm.

46. The body according to claim 45, wherein the body is free or substantially free of radially-distributed defects.

47. A solar cell, comprising the body of silicon according to claims 42 or 45.

48. A solar cell, comprising: a wafer formed from a body of continuous monocrystalline silicon being free or substantially free of radially-distributed impurities and defects, the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm;a p-n junction in the wafer;an optional anti-reflective coating on a surface of the wafer;optionally at least one layer selected from a back surface field and a passivating layer; andelectrically conductive contacts on the wafer.

49. The solar cell according to claim 48, wherein the body is free or substantially free of swirl defects and substantially free of oxygen-induced stacking fault defects.

50. A solar cell, comprising: a wafer formed from a body of continuous cast monocrystalline silicon, the body having at least two dimensions that are each at least about 35 cm;a p-n junction in the wafer;an optional anti-reflective coating on a surface of the wafer;optionally at least one layer selected from a back surface field and a passivating layer; andelectrically conductive contacts on the wafer.

51. The solar cell according to claim 50, wherein the body is free or substantially free of radially-distributed defects.

52. A solar cell, comprising: a continuous monocrystalline silicon wafer formed from a body of continuous cast monocrystalline silicon, the wafer having at least one dimension that is at least about 50 mm, and the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm;a p-n junction in the wafer;an optional anti-reflective coating on a surface of the wafer;optionally at least one layer selected from a back surface field and a passivating layer; andelectrically conductive contacts on the wafer.

53. The solar cell according to claim 52, wherein the wafer is free or substantially free of radially-distributed defects.

54. A wafer, comprising: silicon formed from a body of continuous monocrystalline silicon being free or substantially free of radially-distributed impurities and defects, the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

55. A wafer, comprising: silicon formed from a body of continuous cast monocrystalline silicon, the wafer having at least one dimension that is at least about 50 mm, and the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

56. A method of manufacturing cast silicon, comprising: placing molten silicon in contact with at least one silicon seed crystal in a vessel having one or more side walls heated to at least the melting temperature of silicon and at least one wall for cooling; andforming a solid body of near-monocrystalline silicon, optionally having at least two dimensions each being at least about 10 cm, by cooling the molten silicon to control crystallization, wherein the forming includes forming a solid-liquid interface at an edge of the molten silicon that at least initially parallels the at least one wall for cooling, the interface being controlled during the cooling so as to move in a direction that increases a distance between the molten silicon and the at least one wall for cooling.

57. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 56;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

58. A method of manufacturing cast silicon, comprising: placing molten silicon in contact with at least one silicon seed crystal in a vessel having one or more side walls heated to at least the melting temperature of silicon, the at least one silicon seed crystal arranged to cover an entire or substantially an entire area of a surface of the vessel; andforming a solid body of near-monocrystalline silicon, optionally having at least two dimensions each being at least about 10 cm, by cooling the molten silicon to control crystallization.

59. A method of manufacturing a solar cell, comprising: providing a body of cast silicon according to claim 58;forming at least one wafer from the body;optionally performing a cleaning procedure on a surface of the wafer;optionally performing a texturing step on the surface;forming a p-n junction;optionally depositing an anti-reflective coating on the surface;optionally forming at least one layer selected from a back surface field and a passivating layer; andforming electrically conductive contacts on the wafer.

60. A body of near-monocrystalline silicon being free or substantially free of radially-distributed impurities and defects, and having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

61. A body of near-monocrystalline silicon having a carbon concentration of about 2×1016 atoms/cm3 to about 5×1017 atoms/cm3, an oxygen concentration not exceeding 5×1017 atoms/cm3, a nitrogen concentration of at least 1×1015 atoms/cm3, and having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

62. The body according to claim 60, wherein the body is free or substantially free of swirl defects and substantially free of oxygen-induced stacking fault defects.

63. A body of continuous cast near-monocrystalline silicon having at least two dimensions that are each at least about 35 cm.

64. A solar cell, comprising: a wafer formed from a body of near-monocrystalline silicon being free or substantially free of radially-distributed impurities and defects, the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm;a p-n junction in the wafer;an optional anti-reflective coating on a surface of the wafer;optionally at least one layer selected from a back surface field and a passivating layer; andelectrically conductive contacts on the wafer.

65. A solar cell, comprising: a wafer formed from a body of cast near-monocrystalline silicon, the body having at least two dimensions that are each at least about 35 cm;a p-n junction in the wafer;an optional anti-reflective coating on a surface of the wafer;optionally at least one layer selected from a back surface field and a passivating layer; andelectrically conductive contacts on the wafer.

66. A wafer, comprising: silicon formed from a body of near-monocrystalline silicon being free or substantially free of radially-distributed impurities and defects, the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

67. A wafer, comprising: silicon formed from a body of cast near-monocrystalline silicon, the wafer having at least one dimension that is at least about 50 mm, and the body having at least two dimensions that are each at least about 25 cm and a third dimension at least about 20 cm.

68. Silicon, made according to the method of any one of claims 1, 7, 9, 11, 15, 17, or 19.

69. A wafer, made according to the method of any one of claims 1, 7, 9, 11, 15, 17, or 19.

70. One or more solar cells comprising silicon made according to the method of any one of claims 1, 7, 9, 11, 15, 17, or 19.