Semiconductor solar cells

• US 4,681,983 A
• Filed: 09/18/1985
• Issued: 07/21/1987
• Est. Priority Date: 09/18/1984
• Status: Expired due to Term

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Inventors: Markvart, Tomas, Willoughby, Arthur F. W.
• Primary Examiner(s): Weisstuch, Aaron
• Application Number:
  US06/777,343
• Time in Patent Office: 671 Days
• Field of Search: 136/252, 136/255, 136/261, 136/262, 136/290, 29/572, 29/576 B, 148/1.5, 148/176, 148/DIG. 60
• US Class Current: 136/255
• 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 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/184 the active layers comprising only AIIIBV compounds, e.g. GaAs, InP
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials
• 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
• CPC Class Codes: Y10S 148/06 Gettering

Abstract

A photovoltaic solar cell comprises a piece of semiconductor material incorporating a p-type region, an n-type region, a p-n junction between the two, electrodes contacting the two regions, and within its body a lattice defect denuded zone and a lattice defect gettering zone.

The defect gettering zone may be a precipitate-rich zone or a region of lattice damage. The denuded zone may include the p-n junction.

The semiconductor material may be Si, GaAs or InP.

Methods for making the solar cell are described, involving heat treatment steps to produce a denuded zone, nucleating precipitates and generating precipitates. Alternatively precipitation may be nucleated, or a lattice damage zone may be generated, by proton bombardment.

Claims

1. A photovoltaic solar cell which comprises a piece of Czochralski-grown semiconductor material incorporating a first region which is p-type, a second region which is n-type, a p-n junction between the two and electrodes on different surfaces of the piece, a first electrode making contact with the first region and a second electrode making contact with the second region, wherein the piece incorporates in its body a lattice defect gettering zone and a defect denuded zone extending between the p-n junction and the lattice defect gettering zone, said denuded zone having a thickness of 100 microns or less as measured from a surface of said cell on which solar radiation is intended to fall.

2. A photovoltaic solar cell according to claim 1 wherein the lattice defect gettering zone is a precipitate-rich zone.

3. A photovoltaic solar cell according to claim 2 wherein the precipitate is selected from the group consisting of silicon oxide in silicon, arsenic in gallium arsenide, and phosphorus in indium phosphide.

4. A photovoltaic solar cell according to claim 1 wherein the lattice defect gettering zone is a zone of lattice damage.

5. A solar cell according to claim 1 wherein the region in which the defect denuded zone is formed extends from one surface of the piece to the lattice defect gettering zone, the p-n junction being in this region.

6. A photovoltaic solar cell according to claim 1 wherein the semiconductor material is selected from the group consisting of silicon, germanium, gallium arsenide, and indium phosphide.

7. A photovolatic solar cell according to claim 1 wherein:

(a) the piece of semiconductor material is a single crystalline wafer having the p-n junction formed within the wafer near to a first surface thereof, (b) the region extending from the p-n junction to the first surface is of n⁺ -type material, and the body or substrate of the wafer beneath the p-n junction is of p-type material, (c) the region in which the denuded zone is formed extends from the first surface through the part of the wafer where the n-type layer and the p-n junction are formed and into part of the p-type substrate, and (d) the lattice defect gettering zone is formed in the p-type substrate beneath the denuded zone.

8. A photovoltaic solar cell according to claim 7 wherein the wafer adjacent to the surface thereof remote from the said first surface contains a further denuded zone and a p⁺ -type layer within that denuded zone.

9. A method of making a photovoltaic solar cell comprising the steps of:

(a) applying a denuding heat treatment to a wafer of a Czochralski-grown semiconductor material,

(b) nucleating precipitates at a lower temperature and in an inert atmosphere, and

(c) applying a precipitate yielding anneal at a higher temperature greater than that of step (b) so as to form a denuded zone having a thickness of 100 microns or less as measured from the surface of the cell on which solar radiation is intended to fall.

10. A method according to claim 9 wherein step (b) is replaced by a proton bombardment of the wafer.

11. A method according to claim 9 wherein steps (b) and (c) are replaced by a proton bombardment.