Method for forming structures in a solar cell

• US 8,940,572 B2
• Filed: 04/21/2010
• Issued: 01/27/2015
• Est. Priority Date: 04/21/2009
• Status: Expired due to Fees

• Current Assignee: Tetrasun, Inc. (First Solar Incorporated)
• Original Assignee: Tetrasun, Inc. (First Solar Incorporated)
• Inventors: Turner, Adrian
• Primary Examiner(s): Tornow, Mark
• Assistant Examiner(s): RAMPERSAUD, PRIYA M
• Application Number:
  US13/265,438
• Publication Number:
  US 20120055546A1
• Time in Patent Office: 1,742 Days
• Field of Search: None
• US Class Current: 438/71
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 2103/172 wherein at least one of the layers is non-metallic
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 2103/56 semiconducting semiconducting devices B23K2101/40
• CPC Class Codes: B23K 26/066 by using masks
• CPC Class Codes: B23K 26/073 Shaping the laser spot
• CPC Class Codes: B23K 26/083 Devices involving movement of the workpiece in at least one axial direction
• CPC Class Codes: B23K 26/36 Removing material B23K26/55, B23K26/57 take precedence
• CPC Class Codes: B23K 26/402 involving non-metallic material, e.g. isolators
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/022433 Particular geometry of the grid contacts
• CPC Class Codes: H01L 31/18 Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

A conductive contact pattern is formed on a surface of solar cell by forming a thin conductive layer over at least one lower layer of the solar cell, and ablating a majority of the thin conductive layer using a laser beam, thereby leaving behind the conductive contact pattern. The laser has a top-hat profile, enabling precision while scanning and ablating the thin layer across the surface. Heterocontact patterns are also similarly formed.

Claims

1. A method comprising:

forming a conductive contact pattern on a surface of a solar cell, the solar cell comprising a textured semiconductor substrate surface, the forming comprising;

forming a thin conductive layer over at least one lower layer of the solar cell;

providing a laser beam having a non-Gaussian top hat beam profile;

homogenizing the non-Gaussian top hat beam profile, wherein the textured semiconductor substrate surface is configured to facilitate the homogenizing by having a scale comparable to one or more inhomogeneities in the non-Gaussian tot hat beam profile; and

ablating the entire thin conductive layer from over a portion of the surface using the laser beam having the homogenized non-Gaussian top hat beam profile, thereby leaving behind the conductive contact pattern.

2. The method of claim 1, further comprising forming self-aligned metallization on the conductive contact pattern.

3. The method in accordance with claim 2, wherein a passivation and/or antireflective layer is formed on the surface of the solar cell after said forming said self aligned metallization.

4. The method in accordance with claim 1, wherein the at least one lower layer comprises a passivation and/or antireflective layer beneath the thin conductive layer.

5. The method in accordance with claim 1, wherein the conductive contact pattern forms an electrical contact through the at least one lower layer to a semiconductor layer of the solar cell.

6. The method in accordance with claim 1, further comprising etching or cleaning the conductive contact pattern after said ablating to remove residue, the conductive contact pattern being resistant to said etching or cleaning.

7. The method in accordance with claim 1, wherein the thin conductive layer comprises multiple different thin conductive layers.

8. The method in accordance with claim 1, wherein the providing comprises shaping the laser beam into the non-Gaussian top hat homogeneous beam profile, and the conductive contact pattern comprises a plurality of conductive fingers and a plurality of bus bars interconnected, the plurality of conductive fingers being approximately 50 μ

ms or less.

9. The method in accordance with claim 8, wherein the laser beam is a pulsed laser beam, with the top hat beam profile, processes an area with a single laser pulse, and an overlap of the scanned beam is less than 20% of the single pulse processing area.

10. The method in accordance with claim 1, wherein the laser beam is projected through a mask.

11. The method in accordance with claim 10, wherein a laser beam shape created by the mask is a regular polygon.

12. The method in accordance with claim 10, wherein the laser beam shape created by the mask is the regular polygon obstructed by a thin line running across the polygon.

13. The method in accordance with claim 10, further comprising using multiple mask or a dynamically changing mask.

14. The method in accordance with claim 1, wherein the laser is operated at a wavelength and pulse width at which laser energy is strongly absorbed in the thin layer and weakly absorbed in the at least one lower layer.

15. The method in accordance with claim 1, wherein more than 80% of the surface area of the thin layer is ablated.

16. The method in accordance with claim 1, wherein the pattern remaining after said ablating is in the pattern of contact fingers and/or busbars.

17. A method comprising:

forming a heterocontact pattern on a solar cell, the solar cell comprising a textured semiconductor substrate surface, the forming comprising;

forming a thin layer over at least one lower layer of the solar cell;

providing a laser beam having a non-Gaussian top hat homogeneous beam profile;

homogenizing the non-Gaussian top hat beam profile, wherein the textured semiconductor substrate surface is configured to facilitate the homogenizing by having a scale comparable to one or more inhomogeneities in the non-Gaussian top hat beam profile; and

ablating the entire thin layer from over a portion of the surface using the laser beam having the homogenized non-Gaussian top hat beam profile, thereby leaving behind the heterocontact pattern.

18. The method of claim 17, further comprising forming metallization over the heterocontact pattern to facilitate a conductive connection to the at least one lower layer through the heterocontact pattern.

19. The method in accordance with claim 17, wherein the thin layer comprises multiple different layers.

20. The method in accordance with claim 17, further comprising etching the surface of the solar cell after said ablating to form a surface texture and/or to remove any laser ablation damage, the thin film layer being resistant said etching.

21. The method in accordance with claim 17, further comprising modifying said contact pattern by in-situ heat treatment.

22. The method in accordance with claim 17, wherein all or part of the thin layer comprises a doped semiconductor material.

23. The method in accordance with claim 17, wherein all or part of the thin layer comprises a surface passivation layer.

24. The method in accordance with claim 17, wherein the providing comprises shaping the laser beam into the non-Gaussian top hat homogeneous beam profile, and the heterocontact pattern comprises a plurality of conductive fingers and a plurality of bus bars interconnected, the plurality of conductive fingers being approximately 50 μ

ms or less.

25. The method in accordance with claim 24, wherein the laser beam is a pulsed laser beam, with the top hat beam profile, processes an area with a single laser pulse, and an overlap of the scanned beam is less than 20% of the single pulse processing area.

26. The method in accordance with claim 17, wherein the laser beam is projected through a mask.

27. The method in accordance with claim 26, wherein a laser beam shape created by the mask is a regular polygon.

28. The method in accordance with claim 26, wherein the laser beam shape created by the mask is the regular polygon obstructed by a thin line running across the polygon.

29. The method in accordance with claim 26, further comprising using multiple masks or a dynamically changing mask.

30. The method in accordance with claim 17, wherein the laser is operated at a wavelength and pulse width at which laser energy is strongly absorbed in the thin layer and weakly absorbed in the at least one lower layer.

31. The method in accordance with claim 17, wherein more than 80% of the surface area of the thin layer is ablated.

32. The method in accordance with claim 17, wherein the pattern remaining after said ablating is in the pattern of contact fingers and/or busbars.