Back side contact solar cell with doped polysilicon regions

• US 7,468,485 B1
• Filed: 08/11/2005
• Issued: 12/23/2008
• Est. Priority Date: 08/11/2005
• Status: Active Grant

• Current Assignee: Maxeon Solar Pte Limited
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Swanson, Richard M.
• Primary Examiner(s): Neckel; Alexa D.
• Assistant Examiner(s): BERDICHEVSKY, MIRIAM
• Application Number:
  US11/201,817
• Time in Patent Office: 1,230 Days
• Field of Search: None
• US Class Current: 136/243
• CPC Class Codes: H01L 31/03682 including only elements of Group IV of the Periodic Table
• 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 31/072 the potential barriers being only of the PN heterojunction type
• CPC Class Codes: H01L 31/0745 comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/182 Special manufacturing methods for polycrystalline Si, e.g. Si ribbon, poly Si ingots, thin films of polycrystalline Si
• CPC Class Codes: Y02E 10/546 Polycrystalline silicon PV cells
• 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

In one embodiment, a back side contact solar cell includes a tunnel oxide layer formed on a back side of a substrate. A polysilicon layer is formed on the tunnel oxide layer, and dopant sources are formed on the polysilicon layer. Dopants from the dopant sources are diffused into the polysilicon layer to form p-type and n-type regions therein. The p-type and n-type regions form p-n junctions that, among other advantages, allow for relatively high conversion efficiency.

Claims

1. A method of fabricating a back side contact solar cell, the method comprising:

forming a first tunnel oxide layer over a back side of a solar cell substrate;

forming a first polysilicon layer over the first tunnel oxide layer;

forming a p-type dopant source and an n-type dopant source over the first polysilicon layer; and

doping the first polysilicon layer by diffusing dopants from the p-type dopant source and the n-type dopant source into the first polysilicon layer to form a p-type region and an n-type region in a continuous portion of the first polysilicon layer, the p-type region and the n-type region in the first polysilicon layer forming a p-n junction of the solar cell.

2. The method of claim 1 wherein the first tunnel oxide layer is formed to a thickness of about 10 Angstroms.

3. The method of claim 1 wherein the p-type dopant source comprises a boron-doped silicon dioxide.

4. The method of claim 1 wherein the n-type dopant source comprises a phosphorus-doped silicon dioxide.

5. The method of claim 1 further comprising:

forming a second tunnel oxide layer over a front side of the solar cell substrate;

forming a second polysilicon layer over the second tunnel oxide layer;

forming a second n-type dopant source over the second polysilicon layer; and

doping the second polysilicon layer by diffusing dopants from the second n-type dopant source into the second polysilicon layer.

6. The method of claim 1 further comprising:

texturing a front side of the solar cell substrate.

7. The method of claim 6 further comprising:

diffusing n-type dopants into the solar cell substrate by way of the front side of the solar cell substrate.

8. The method of claim 1 wherein a first undoped silicon dioxide layer is formed between the p-type dopant source and the n-type dopant source prior to doping the first polysilicon layer.

9. The method of claim 8 wherein a second undoped silicon dioxide layer is formed over the n-type dopant source prior to doping the first polysilicon layer to prevent dopants from the n-type dopant source from escaping into a furnace environment during the doping of the first polysilicon layer.

10. A back side contact solar cell comprising:

a substrate having a front side and a back side, the front side of the substrate being configured to face the sun to receive solar radiation during normal operation;

a first tunnel oxide layer formed over the back side of the substrate;

a first doped polysilicon layer formed over the first tunnel oxide layer, the first doped polysilicon layer having a plurality of p-type and n-type regions in a continuous portion, each adjacent p-type region and n-type region in the plurality of p-type and n-type regions forming a p-n junction of the solar cell; and

metal contacts coupled to the p-type and n-type regions, the metal contacts being configured to allow an external device to be coupled to the solar cell.

11. The back side contact solar cell of claim 10 further comprising:

an anti-reflective coating formed over a textured surface on the front side of the substrate.

12. The back side contact solar cell of claim 10 further comprising:

a p-type dopant source formed over the first doped polysilicon layer; and

an n-type dopant source formed over the p-type dopant source and the first doped polysilicon layer.

13. The back side contact solar cell of claim 12 further comprising:

an undoped silicon dioxide layer formed between the p-type dopant source and the n-type dopant source.

14. The back side contact solar cell of claim 10 wherein the p-type dopant source comprises boron-doped silicon dioxide.

15. The back side contact solar cell of claim 10 wherein the n-type dopant source comprises phosphorus-doped silicon dioxide.

16. The back side contact solar cell of claim 10 further comprising:

a second tunnel oxide layer formed over a textured surface on the front side of the substrate; and

a second doped polysilicon layer formed over the second tunnel oxide layer.

17. The back side contact solar cell of claim 16 wherein the second doped polysilicon layer is doped with an n-type dopant.

18. The back side contact solar cell of claim 16 further comprising an n-type dopant source formed over the second doped polysilicon layer.

19. A back side contact solar cell comprising:

a silicon wafer;

a tunnel oxide layer formed on a back side of the wafer; and

a doped polysilicon layer formed on the tunnel oxide layer, the doped polysilicon layer having a continuous portion having boron-doped regions and phosphorus-doped regions, each adjacent boron-doped region and phosphorus-doped region forming a p-n junction of the solar cell.

20. The back side contact solar cell of claim 19 further comprising:

metal contacts formed to connect to the boron-doped and phosphorus-doped regions for allowing the solar cell to be coupled to an external circuit.