Interdigitated Back Contact Silicon Solar Cells With Laser Ablated Grooves

• US 20100059109A1
• Filed: 09/09/2008
• Published: 03/11/2010
• Est. Priority Date: 09/09/2008
• Status: Active Grant

• Current Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Nakayashiki, Kenta, Xu, Baomin
• Granted Patent: US 7,999,175 B2
• Time in Patent Office: Days
• US Class Current: 136/255
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact solar cells
• CPC Class Codes: H01L 31/0682 back-junction, i.e. rearside emitter, solar cells, e.g. interdigitated base-emitter regions back-junction cells
• 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

Interdigitated back contact (IBC) solar cells are produced by depositing spaced-apart parallel pads of a first dopant bearing material (e.g., boron) on a substrate, heating the substrate to both diffuse the first dopant into corresponding first (e.g., p+) diffusion regions and to form diffusion barriers (e.g., borosilicate glass) over the first diffusion regions, and then disposing the substrate in an atmosphere containing a second dopant (e.g., phosphorus) such that the second dopant diffuses through exposed surface areas of the substrate to form second (e.g., n+) diffusion regions between the first (p+) diffusion regions (the diffusion barriers prevent the second dopant from diffusion into the first (p+) diffusion regions). The substrate material along each interface between adjacent first (p+) and second (n+) diffusion regions is then removed (e.g., using laser ablation) such that elongated grooves, which extend deeper into the substrate than the diffused dopant, are formed between adjacent diffusion regions.

Claims

1. An IBC solar cell comprising

a substrate having a rear surface and an opposing front surface;

a plurality of interdigitated diffusion regions formed in the rear surface of the substrate, the plurality of interdigitated diffusion regions including a first diffusion region and a second diffusion region having a first doping concentration and extending a first depth into the substrate from the rear surface, and a third diffusion region having a second doping concentration and extending a second depth into the substrate from the rear surface, the third diffusion region being disposed between the first and second diffusion regions; and

a plurality of grooves defined into the rear surface of the substrate between adjacent pairs of said plurality of interdigitated diffusion regions such that the first diffusion region is separated from the third diffusion region by a first groove, and the second diffusion region is separated from the third diffusion region by a second groove,

wherein each of said plurality of grooves having a third depth into the substrate from the rear surface that is greater than the first and second depths.

2. The IBC solar cell according to claim 1, wherein the first and second diffusion regions comprise a p-type dopant, and wherein the third diffusion region comprises an n-type dopant.

3. The IBC solar cell according to claim 1, wherein the substrate comprises an n-type substrate.

4. The IBC solar cell according to claim 1, wherein the substrate comprises an p-type substrate.

5. The IBC solar cell according to claim 1, wherein the depth of each of said plurality of grooves is in the range of 0.2 to 10 m, and wherein each of said plurality of grooves has a width in the range of 1 to 50 μ

m.

6. The IBC solar cell according to claim 1, wherein the depth of each of said plurality of grooves is in the range of 0.5 to 1.5 μ

m, and wherein each of said plurality of grooves has a width in the range of 1 to 10 μ

m.

7. An IBC solar cell according to claim 1, further comprising a fourth diffusion region formed in the front surface of the substrate, the fourth diffusion region having the second doping concentration and extending a second depth into the substrate from the rear surface.

8. An IBC solar cell according to claim 7, further comprising a passivation layer disposed over the rear surface of the substrate, wherein the passivation layer includes portions respectively disposed in each of said plurality of grooves.

9. An IBC solar cell according to claim 8, further comprising a plurality of metal contacts extending through the passivation layer, wherein each said metal contact abuts a corresponding one of said plurality of diffusion regions.

10. A method of fabricating an IBC solar cell, the method comprising:

diffusing a first dopant into a rear surface of a semiconductor substrate such that first and second spaced-apart diffusion regions of the substrate have a first doping concentration and extends a first depth into the substrate from the rear surface, and are separated by a third diffusion region having a second doping concentration and extending a second depth into the substrate from the rear surface; and

form a plurality of grooves into the rear surface of the semiconductor substrate such that the first diffusion region is separated from the third diffusion region by a first groove, and the second diffusion region is separated from the third diffusion region by a second groove.

11. The method according to claim 10, wherein diffusing the first dopant comprises:

depositing spaced-apart pads of said first dopant onto the rear surface of substrate over said first and second diffusion regions; and

heating the substrate such that a portion of the first dopant diffuses into said first and second diffusion regions through said rear surface, wherein the second doping concentration of the third diffusion region maintains said second doping concentration during said heating.

12. The method according to claim 10, wherein depositing the spaced-apart pads of said first dopant comprises one of extrusion, screen printing, pad printing or jet printing said first dopant onto said rear surface.

13. The method according to claim 12,

wherein said first dopant comprises boron, and

wherein heating comprises forming borosilicate glass on said rear surface over said first and second diffusion regions.

14. The method according to claim 13, further comprising, after forming said borosilicate glass, diffusing a n-type dopant into said third diffusion region such that said borosilicate glass prevent diffusion of said n-type dopant into said first and second diffusion regions.

15. The method according to claim 14, wherein diffusing the n-type dopant comprises disposing said substrate in a furnace containing POCl₃ at a temperature below 900°

C.

16. The method according to claim 11, further comprising, after said first dopant material is diffused into said first and second diffusion regions, diffusing a second dopant material into said third diffusion region such that said first dopant in said first and second diffusion regions serves as a diffusion barrier, whereby said third diffusion region acquires a third doping concentration determined by said second dopant material, and said first and second diffusion regions maintain said first doping concentration.

17. The method according to claim 11, wherein the forming of a plurality of grooves on the rear surface of the substrate comprises selectively laser ablating the rear surface of the substrate.

18. The method according to claim 11, wherein the forming of a plurality of grooves on the rear surface of the substrate comprises selectively chemical etching the rear surface of the substrate.

19. A method of fabricating an IBC solar cell, the method comprising:

diffusing a first dopant into a rear surface of a semiconductor substrate such that first and second spaced-apart diffusion regions of the substrate have a first doping concentration and extends a first depth into the substrate from the rear surface, and are separated by a third diffusion region having a second doping concentration and extending a second depth into the substrate from the rear surface; and

diffusing a second dopant into said third diffusion region such that said first dopant prevents diffusion of said second dopant into said first and second diffusion regions.

20. The method according to claim 19, wherein diffusing the first dopant comprises:

depositing spaced-apart pads of material containing boron onto the rear surface of substrate over said first and second diffusion regions; and

heating the substrate such that a first portion of the boron diffuses into said first and second diffusion regions through said rear surface, and a second portion of the boron forms borosilicate glass on said rear surface over said first and second diffusion regions.

21. The method according to claim 20, further comprising, after forming said borosilicate glass, disposing said substrate in a furnace containing POCl₃ at a temperature selected such that phosphorus is diffused into said third diffusion region and said borosilicate glass prevents diffusion of said n-type dopant into said first and second diffusion regions.

22. The method according to claim 19, further comprising forming a plurality of grooves into the rear surface of the substrate such that the first diffusion region is separated from the third diffusion region by a first groove, and the second diffusion region is separated from the third diffusion region by a second groove.