SOLAR CELL FABRICATION WITH FACETING AND ION IMPLANTATION

• US 20090308450A1
• Filed: 06/11/2009
• Published: 12/17/2009
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Intevac
• Original Assignee: Solar Implant Technologies, Inc. (Intevac, Inc.)
• Inventors: Murrer, Edward S., Adibi, Babak
• Granted Patent: US 8,697,553 B2
• Time in Patent Office: Days
• US Class Current: 136/256
• CPC Class Codes: H01L 21/26506 in group IV semiconductors
• CPC Class Codes: H01L 21/26513 of electrically active species
• CPC Class Codes: H01L 21/2658 of a molecular ion, e.g. decaborane
• CPC Class Codes: H01L 21/266 using masks H01L21/26586 takes precedence
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/072 the potential barriers being only of the PN heterojunction type
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

Solar cells in accordance with the present invention have reduced ohmic losses. These cells include photo-receptive regions that are doped less densely than adjacent selective emitter regions. The photo-receptive regions contain multiple four-sided pyramids that decrease the amount of light lost to the solar cell by reflection. The smaller doping density in the photo-receptive regions results in less blue light that is lost by electron-hole recombination. The higher doping density in the selective emitter region allows for better contacts with the metallic grid coupled to the multiple emitter regions. Preferably, the selective emitter and photo-receptive regions are both implanted using a narrow ion beam containing the dopants.

Claims

1. A semiconductor device comprising:

a substrate having a surface that contains textured regions doped with a dopant to a first doping level and non-textured regions forming gridlines and doped with the dopant to a second doping level larger than the first doping level; and

conductive fingers coupled to the gridlines.

2. The semiconductor device of claim 1, wherein the textured-regions are photo-receptive.

3. The semiconductor device of claim 1, wherein each of the textured regions comprises multiple textured elements.

4. The semiconductor device of claim 3, wherein each of the textured elements is pyramidal shaped.

5. The semiconductor device of claim 4, wherein each of the textured elements has a <

111>

plane.

6. The semiconductor device of claim 3, wherein each of the textured elements is dome shaped.

7. The semiconductor device of claim 3, wherein a thickness of the dopant on each of the multiple textured elements is uniform.

8. The semiconductor device of claim 1, wherein each of the textured regions is covered with an anti-reflective coating.

9. The semiconductor device of claim 1, wherein the dopants are n-type and the substrate is p-type.

10. The semiconductor substrate of claim 1, wherein the dopants are p-type and the substrate is n-type.

11. The semiconductor device of claim 1, wherein the dopants in the non-textured regions are interspersed with a metallic species.

12. The semiconductor device of claim 1, wherein the substrate has a bottom portion coupled to a metallic contact containing impurities.

13. A method of fabricating a solar cell comprising:

exposing a surface of a substrate having non-textured and textured regions to ions, thereby implanting dopants into the textured regions at a first density and into the non-textured regions at a second density larger than the first density to form gridlines; and

coupling contact fingers to the gridlines.

14. The method of claim 13, wherein the textured regions each comprise multiple textured elements.

15. The method of claim 14, wherein the multiple textured elements are pyramidal.

16. The method of claim 14, wherein the multiple textured elements are semi-spherical.

17. The method of claim 13, wherein exposing the surface comprises directing an ion beam containing the dopants onto the surface.

18. The method of claim 17, wherein the beam is shaped to implant dopants into each of the multiple textured elements individually.

19. The method of claim 17, further comprising linearly scanning the beam across the surface to thereby implant the dopants.

20. The method of claim 13, wherein exposing the surface comprises engulfing the surface with a plasma beam.

21. The method of claim 13, wherein the textured regions are photo-receptive.

22. The method of claim 13, further comprising rotating a source of the ions, the substrate, or both so that the ion source is substantially perpendicular to faces of each of the multiple textured elements.

23. The method of claim 13, wherein a resistance of the dopant in the non-textured regions is about 20 ohms/square.

24. The method of claim 13, wherein a resistance of the dopant in the textured regions is about 100 ohms/square.

25. The method of claim 13, further comprising coupling the gridlines to metallic contact fingers.

26. The method of claim 25, further comprising forming a silicide between the gridlines and the contact fingers.

27. A method of fabricating a solar cell comprising:

etching a top surface of a substrate to form textured photo-receptive regions among planar regions, wherein the textured regions comprise pyramidal shaped elements;

directing an ion beam onto the top surface, thereby implanting dopants into the textured regions at a first density and into the planar regions at a second density larger than the first density to form gridlines, wherein a resistance of the dopant in the textured regions is less than 100 ohms per square and a resistance of the dopant in the planar regions is about 20 ohms per square; and

coupling contact fingers to the gridlines.

28. A solar cell comprising:

a substrate having a top layer and a bottom layer, wherein the top layer has a surface containing pyramidal regions doped with a dopant to a first doping level and substantially planar regions forming gridlines and doped with the dopant to a second doping level larger than the first doping level, distances between adjacent substantially planar regions are less than 50 microns, and the substrate having a thickness of less than 50 microns;

silicide elements coupling the gridlines to metallic fingers; and

a contact coupled to the bottom layer.

29. A system for fabricating solar cells comprising:

a source for producing ions;

a beam shaper to direct a beam containing the ions onto a substrate; and

a controller programmed to direct the beam onto the substrate such that a textured photo-receptive region of the substrate is implanted with the ions to a first density and a planar region of the substrate defining a gridline is implanted with the ions to a second density larger than the first density.

30. The system of claim 29, wherein the controller is also programmed to step the beam to individually implant textured elements in the photo-receptive region.

31. The system of claim 30, wherein the controller is also programmed to perform any combination of rotating, tilting, or translating the substrate when the beam is directed onto the substrate.

32. The system of claim 30, wherein the controller is programmed to direct the beam so that a resistance of the photo-receptive region is about 100 ohms per square.

33. The system of claim 30, wherein the controller is programmed to direct the beam so that a resistance of the planar region is about 10 ohms per square.