Solar cells composed of semiconductive materials

• US 4,253,881 A
• Filed: 10/10/1979
• Issued: 03/03/1981
• Est. Priority Date: 10/23/1978
• Status: Expired due to Term

• Current Assignee: NUKEM GmbH (Cameco Corporation)
• Original Assignee: Rudolf Hezel
• Inventors: Hezel, Rudolf
• Primary Examiner(s): Weisstuch, Aaron
• Application Number:
  US06/083,248
• Time in Patent Office: 510 Days
• Field of Search: 136/89 CC, 136/89 SJ, 357/30, 357/54
• US Class Current: 136/256
• CPC Class Codes: H01L 31/02167 for solar cells
• CPC Class Codes: H01L 31/062 the potential barriers being only of the metal-insulator-semiconductor type
• CPC Class Codes: H01L 31/068 the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
• CPC Class Codes: H01L 31/0693 the devices including, apart from doping material or other impurities, only AIIIBV compounds, e.g. GaAs or InP solar cells
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

A solar cell is composed of a semiconductive material having an active zone in which charge carriers are produced by photons which strike and penetrate into the solar cell. The cell is comprised of a semiconductive body having an electrically insulating laminate with metal contacts therein positioned on the semiconductor body in the active zone thereof. The insulating laminate is composed of a double layer of insulating material, with the layer in direct contact with the semiconductive surface being composed of SiO₂ which is either natural or is produced at temperatures below 800° C. and the layer superimposed above the SiO₂ layer being composed of a different insulating material, such as plasma-produced Si₃ N₄. In certain embodiments of the invention, a whole-area pn-junction is provided parallel to the semiconductive surface. The solar cells of the invention exhibit a higher degree of efficiency due to a higher fixed interface charged density, and low surface recombination velocity, an increased UV sensitivity, improved surface protection and passivation and improved anti-reflection characteristics relative to prior art solar cell devices.

Claims

1. A solar cell having a body composed of a semiconductive material with an active zone in which charge carriers are generated by energy impinging upon such cell and penetrating into it, said cell having an electrically insulating layer on the incident surface of said semiconductive material comprised of a double layer with metal contacts positioned therein and overlying said active zone, said double layer consisting of a first layer having a thickness greater than 0 and less than about 4 nm and being directly applied onto said semiconductive body and being composed of a material selected from the group consisting of natural silicon oxide and a silicon oxide generated at temperatures below 800°

C., and a second layer directly applied onto said first layer and being composed of a material selected from the group consisting of silicon nitride and silicon oxynitride.

2. A solar cell as defined in claim 1 wherein the total thickness of said double layer is less than about 5.5 nm.

3. A solar cell as defined in claim 1 wherein the thickness of said second layer is in the range of about 50 to 300 nm.

4. In a solar cell as defined in claim 1 wherein said second layer is composed of silicon nitride which is produced by deposition from a gas phase in a reaction furnace means.

6. In a solar cell as defined in claim 1 wherein said second layer is composed of a material selected from the group consisting of silicon nitride and silicon oxynitride, and said second layer includes foreign ions deliberately incorporated therein.

7. In a solar cell as defined in claim 6 wherein said foreign ions are alkali ions.

8. In a solar cell as defined in claim 1 wherein said metallic contacts at least partially penetrate into said second layer.

9. In a solar cell as defined in claim 1 wherein said metal contacts penetrate through said first and second layers and contact a highly doped zone on said semiconductive body.

10. In a solar cell as defined in claim 9 wherein said highly-doped zone is produced via diffusion or ion implantation.

11. In a solar cell as defined in claim 1 wherein said first layer has a thickness less than about 2 nm, said second layer has a thickness in the range of about 2 to 3 nm and a transparent metal layer is provided above said second layer and covers the surface areas between said metallic contacts.

12. In a solar cell as defined in claim 1 wherein said first layer has a thickness of less than about 2 nm, said second layer has a thickness in the range of about 1 to 4 nm, said metallic contacts being directly applied onto said second layer and a third insulating layer having a thickness in the range of about 50 to 300 nm is applied between and above said metallic contacts.

13. In a solar cell as defined in claim 12 wherein said third layer is composed of silicon nitride.

14. In a solar cell as defined in claim 1 wherein said semiconductive body is provided with spaced-apart highly-doped zones produced via diffusion or ion implantation and said metallic contacts penetrate said first layer above said highly doped zones so as to contact such zones and said second insulating layer having a thickness in the range of about 50 to 300 nm is applied between and above said metallic contacts.

15. In a solar cell as defined in claim 1 wherein said semiconductive body is provided with a whole-area pn-junction arranged parallel with a surface of said body and said metallic contacts penetrate said first layer so as to contact said pn-junction, and said second insulating layer having a thickness in the range of about 50 to 300 nm is applied between and above said metallic contacts.

16. In a solar cell as defined in claim 15 wherein said pn-junction has a depth within said semiconductive body ranging between about 0.05 to 0.5 μ

m.

17. In a solar cell as defined in claim 16 wherein said pn-junction is produced via ion implantation.

18. In a solar cell as defined in claim 16 wherein said pn-junction is produced via diffusion.

19. In a solar cell as defined in claim 15 wherein said second layer is composed of silicon nitride and has a thickness adapted for optimum anti-reflection characteristics.

20. In a solar cell as defined in claim 19 wherein said semiconductive material forming said solar cell body is silicon and said silicon nitride second layer has a thickness of about 80 nm.

21. In a solar cell as defined in claim 19 wherein said silicon nitride comprises a plasma-produced nitride.

22. In a solar cell as defined in claim 1 wherein said semiconductive material forming said solar cell body is selected from the group consisting of monocrystalline semiconductive material, polycrystalline semiconductive material, amorphous semiconductive material, silicon, germanium and A^III B^V compounds.

23. In a solar cell as defined in claim 22 wherein said semiconductive material comprises p-doped silicon.

5. In a solar cell as defined in 1 wherein said second layer is composed of silicon nitride which is produced by deposition from a gas phase in a glow discharge.