Variegated, high efficiency solar cell and method for making same

• US 20040025932A1
• Filed: 08/12/2002
• Published: 02/12/2004
• Est. Priority Date: 08/12/2002
• Status: Abandoned Application

• Current Assignee: Micrel Incorporated (Microchip Technology Incorporated)
• Original Assignee: Micrel Incorporated (Microchip Technology Incorporated)
• Inventors: Husher, John
• Application Number:
  US10/218,687
• Publication Number:
  US 20040025932A1
• Time in Patent Office: Days
• US Class Current: 136/256
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact solar cells
• CPC Class Codes: H01L 31/02363 of the semiconductor body itself, e.g. textured active layers
• CPC Class Codes: H01L 31/035281 Shape of the body
• CPC Class Codes: H01L 31/03529 Shape of the potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/061 the potential barriers being of the point-contact type H01L31/07 takes precedence
• 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: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

A solar cell is provided comprising a substrate having a light-receiving first surface and a variegated second surface, the second surface having at least first and second recesses. The substrate is doped within the first recess to provide a p-type region, and within the second recess to provide an n-type region. At least one conductive material is disposed in each of the first and second recesses, permitting electrical connections to the p-type and n-type regions. In a first embodiment, using selective deposition, tungsten fills the slots and slots may have a depth of up to 60 microns. In a second embodiment, a sputtering technique is used to deposit metal in the slots, and slots may have a depth of up to about 10 microns.

Claims

1. A solar cell comprising a substrate having a light-receiving first surface and a variegated second surface, the second surface defining a first recess, the substrate being doped within the first recess to provide a first doped region defining the first recess and at least one conductive material disposed in each of the first recesses for permitting electrical connections to the doped region.

2. A solar cell according to claim 1, wherein said conductive material comprises tungsten.

3. A solar cell according to claim 1, wherein said second surface further defines a second recess, the substrate being doped within the second recess to provide a second doped region, and wherein said first doped region is a p-type region and said second doped region is an n-type region.

4. The solar cell of claim 3 wherein the substrate is doped with boron within the first recess to provide a p-type region defining the first recess.

5. The solar cell of claim 3 wherein the substrate is doped with and element chosen from the group consisting of Phosphorous and Arsenic within the second recess to provide a n-type region defining the second recess.

6. The solar cell of claim 3 wherein said first and second recesses comprise first and second slots.

7. The solar cell of claim 3, wherein said first and second slots are provided simultaneously.

8. The solar cell of claim 3 wherein the second surface defines a plurality of first recesses and a plurality of second recesses.

9. The solar cell of claim 8, wherein said plurality of first and second recess are all provided in one step.

10. The solar cell of claim 3 wherein the first and second recesses extend parallel to each other.

11. The solar cell of claim 3, wherein said at least one conductive material includes tungsten.

12. The solar cell of claim 3, wherein said at least one conductive material includes tungsten and aluminum.

13. The solar cell of claim 3, wherein tungsten completely fills at least one of said slots.

14. The solar cell of claim 3, further comprising

a first bonding pad electrically connected to said at least one conductive material disposed in said p-type recess;

and

a second bonding pad electrically connected to said at least one conductive material disposed in said n-type recess.

15. The solar cell of claim 6, wherein each of said slots ranges from 25 to 60 microns in length and 5 to 20 microns in width.

16. The solar cell of claim 3, wherein said substrate comprises silicon.

17. A method for forming a solar cell from a substrate having a first light-receiving surface and an opposite second surface, comprising the steps of:

(a) forming a first and second recess extending through the second surface;

(b) providing a p-type region defining the first recess;

(c) providing a n-type region defining the second recess; and

(d) selectively providing at least one conductive material in said recesses by chemical reaction.

18. The method of claim 17, wherein the p-type region defining the first recess comprises Boron doped silicon.

19. The method of claim 17, wherein the n-type region defining the second recess comprises silicon doped with an element chosen from the group consisting of Phosphorous and Arsenic.

20. The method of claim 17, wherein said first and second recess are formed as first and second slots.

21. The method of claim 20, wherein said first and second slots are formed in one step.

22. The method of claim 17, wherein a plurality of first recess and a plurality of second recesses are formed.

23. The method of claim 22, wherein said plurality of first and second recesses are all provided in one step.

24. The method of claim 17, further comprising the step of depositing a second conductive material in said recesses.

25. The method of claim 17, wherein said first conductive material is tungsten.

26. The method of claim 24, wherein said first conductive material is tungsten and said second conductive material is aluminum.

27. The method of claim 17, further comprising the step of:

oxidizing said substrate at a temperature greater than approximately 450 degrees Celsius after said metallization step.

28. The method of claim 20 wherein said selectively depositing step includes the step of generating tungsten on a silicon substrate by means of chemical reaction followed by thickening the tungsten by vapor deposition.

29. The method of claim 28 wherein said depositing tungsten comprises providing a patterned masking layer on said second substrate surface and introducing WF6 gas to said substrate such that tungsten is selectively deposited in said first and second recesses.

30. The method of claim 28 wherein said selectively depositing step further comprises thickening said tungsten by reacting hydrogen gas with said WF6.

31. The method of claim 17, wherein said substrate is silicon and wherein providing said p-type region comprises:

oxidizing said substrate such that silicon dioxide is formed along the surface of said recess;

patterning said silicon dioxide to expose said p-type recess;

exposing said substrate to boron in an oxidizing atmosphere.

32. The method of claim 30, wherein providing said n-type region comprises:

patterning said silicon dioxide to expose said n-type slots;

exposing said substrate to a dopant chosen from the group consisting of Phosphorous and Arsenic.

33. The method of claim 17, further comprising the step of

performing a rapid thermal processing oxidation at about 450 degrees Celsius.

35. The method of claim 33 further comprising:

(e) planarizing said substrate such that conductive material remains in said recesses.

34. A method for forming a solar cell from a substrate having a first light-receiving surface and an opposite second surface, comprising the steps of:

(a) forming a first and second recess extending through the second surface;

(b) providing a p-type region defining the first recess;

(c) providing a n-type region defining the second recess; and

(d) depositing a conductive material in said recess under conditions sufficient for the material to flow into the recesses.

36. The method of claim 34 further comprising:

depositing a second layer of conductive material in said recesses.