Induced junction solar cell and method of fabrication

• US 4,090,213 A
• Filed: 06/15/1976
• Issued: 05/16/1978
• Est. Priority Date: 06/15/1976
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Maserjian, Joseph, Chern, Shy Shiun, Li, Seung P.
• Primary Examiner(s): Edlow, Martin H.
• Application Number:
  US05/696,374
• Time in Patent Office: 700 Days
• Field of Search: 357/30, 357/52, 357/91, 148/1.5
• US Class Current: 136/255
• CPC Class Codes: H01L 31/062 the potential barriers being only of the metal-insulator-semiconductor type
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy
• CPC Class Codes: Y10S 438/91 Controlling charging state at semiconductor-insulator interface

Abstract

An induced junction solar cell is fabricated on a p-type silicon substrate by first diffusing a grid of criss-crossed current collecting n⁺ stripes and thermally growing a thin SiO₂ film, and then, using silicon-rich chemical vapor deposition (CVD), producing a layer of SiO₂ having inherent defects, such as silicon interstices, which function as deep traps for spontaneous positive charges. Ion implantation increases the stable positive charge distribution for a greater inversion layer in the p-type silicon near the surface. After etching through the oxide, to parallel collecting stripes, a pattern of metal is produced consisting of a set of contact stripes over the exposed collecting stripes and a diamond shaped pattern which functions as a current collection bus. Then the reverse side is metallized.

Claims

1. An induced junction solar cell comprising

a substrate of p-type semiconductor material,

a pattern of current collecting stripes on one broad side of said substrate diffused with n-type impurities,

a film of dielectric material on said one side of said substrate,

a layer of dielectric material produced over said dielectric film,

a uniform concentration of positive ions implanted in said dielectric layer,

a pattern of metal conductors in ohmic contact with said current collecting stripes, and

a film of metal in ohmic contact with said substrate on the other side of said substrate opposite said one side.

2. An induced junction solar cell as defined in claim 1 wherein said uniform concentration of ions is in excess of 0.5 ×

10¹² per square centimeter.

3. An induced junction solar cell as defined in claim 1 wherein said uniform concentration of ions is about 8 ×

10¹² per square centimeter.

4. An induced junction solar cell as defined in claim 1 wherein said uniform concentration of ions is a maximum stable concentration produced by implanting ions in excess of that necessary to produce a stable concentration.

5. An induced junction solar cell as defined in claim 1 wherein said film is a thermally grown oxide of said semiconductor material, and said layer is an oxide of said semiconductor material produced by chemical vapor deposition with inherent defects which function as deep traps for spontaneous positive charges.

6. An induced junction solar cell as defined in claim 5 wherein said uniform concentration of ions is in excess of 0.5 ×

10¹² per square centimeter.

7. An induced junction solar cell as defined in claim 5 wherein said uniform concentration of ions is about 8 ×

10¹² per square centimeter.

8. An induced junction solar cell as defined in claim 5 wherein said uniform concentration of ions is a maximum stable concentration produced by implanting ions in excess of that necessary to produce a stable concentration.

9. An induced junction solar cell as defined in claim 1 wherein said pattern of stripes is comprised of crisscrossed stripes, each about 1 mil wide, said stripes being uniformly spaced about 10 mils apart in both orthogonal directions.

10. An induced junction solar cell comprising

a substrate of semiconductor material of a given conductivity type having a broad obverse side through which solar energy is to be received and a reverse side opposite said obverse side,

a crisscrossed grid of current collecting stripes of opposite conductivity type diffused into said substrate on the obverse side,

a thin film of dielectric material on the obverse side of said substrate over said collecting stripes and all areas between said collecting stripes except over collecting stripes of said crisscross pattern which are oriented in one direction,

a layer of dielectric material on said thin film having a maximum concentration of stable charges of said given conductivity type distributed throughout to induce a field of opposite charge in said substrate near the surface thereof, except over collecting stripes of said crisscross pattern which are oriented in said one direction,

a pattern of metal stripes in ohmic contact with said collecting stripes oriented in said one direction and a bus bar interconnecting said metal stripes, and

a film of metal in ohmic contact with said substrate on the reverse side thereof.

11. An induced junction solar cell as defined in claim 10 wherein said maximum concentration of stable charges of said given conductivity type is comprised of ions implanted in said dielectric layer.

12. An induced junction solar cell as defined in claim 11 wherein said dielectric layer is comprised of an oxide produced by chemical vapor deposition, whereby said layer is provided with inherent defects that function as deep traps for spontaneous positive charges.

13. A method for the preparation of semiconductor material of a given conductivity type for a solar cell using an induced junction in a substrate of said semiconductor material for the conversion of radiation into electrical energy, comprising

diffusing a pattern of stripes on a broad surface of said substrate, said stripes being of a conductivity type opposite said given conductivity type,

producing a thin uniform dielectric film over said surface,

producing a uniform dielectric layer over said film,

implanting a uniform concentration of ions in said dielectric layer, said ions being of the same polarity as the conductivity of said semiconductor material, and

producing a pattern of metal conductors in ohmic contact with stripes of said pattern to collect current from all stripes and a bus bar to collect current from all conductors.

14. A method as defined in claim 13 wherein said uniform concentration of ions is in excess of 0.5 ×

10¹² per square centimeter.

15. A method as defined in claim 13 wherein said uniform concentration of ions is about 8 ×

10¹² per square centimeter.

16. A method as defined in claim 13 wherein said uniform concentration of ions is a maximum stable concentration produced by implanting ions in excess of that necessary to produce a stable concentration.

17. A method as defined in claim 13 wherein said semiconductor material is silicon, said thin dielectric film is produced by thermal oxidation on said surface and said dielectric layer is produced by chemical vapor deposition of silicon dioxide on said thin film.

18. A method as defined in claim 17 wherein said semiconductor material is p-type silicon, and said ions implanted are positive.

19. A method as defined in claim 18 wherein said uniform concentration of ions is in excess of 0.5 ×

10¹² per square centimeter.

20. A method as defined in claim 18 wherein said uniform concentration of ions is about 8 ×

10¹² per square centimeter.

21. A method as defined in claim 18 wherein said uniform concentration of ions is a maximum stable concentration produced by implanting ions in excess of that necessary to produce a stable concentration.