MICROWAVE ANNEAL OF A THIN LAMINA FOR USE IN A PHOTOVOLTAIC CELL

• US 20110143480A1
• Filed: 12/11/2009
• Published: 06/16/2011
• Est. Priority Date: 12/11/2009
• Status: Active Grant

• Current Assignee: Neutron Therapeutics Inc.
• Original Assignee: Twin Creeks Technologies, Inc.
• Inventors: Venkatesan, Murali, Prabhu, Gopal, Li, Zhiyong, Hilali, Mohamed M.
• Granted Patent: US 8,257,995 B2
• Time in Patent Office: Days
• US Class Current: 438/58
• CPC Class Codes: H01L 21/324 Thermal treatment for modifying the properties of semiconductor bodies, e.g. annealing, sintering H01L21/20 - H01L21/288 and H01L21/302 - H01L21/322 take precedence
• CPC Class Codes: H01L 31/056 the light-reflecting means being of the back surface reflector [BSR] 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 31/0747 comprising a heterojunction of crystalline and amorphous materials, e.g. heterojunction with intrinsic thin layer
• CPC Class Codes: H01L 31/1864 Annealing
• CPC Class Codes: H01L 31/1872 Recrystallisation
• CPC Class Codes: H01L 31/1892 methods involving the use of temporary, removable substrates
• CPC Class Codes: Y02E 10/52 PV systems with concentrators
• 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

A cleave plane is defined in a semiconductor donor body by implanting ions into the wafer. A lamina is cleaved from the donor body, and a photovoltaic cell is formed which comprises the lamina. The implant may cause some damage to the crystal structure of the lamina. This damage can be repaired by annealing the lamina using microwave energy. If the lamina is bonded to a receiver element, the receiver element may be either transparent to microwaves, or may reflect microwaves, while the semiconductor material absorbs the microwaves. In this way the lamina can be annealed at high temperature while the receiver element remains cooler.

Claims

1. A method to form a photovoltaic cell, the method comprising the steps of:

providing a semiconductor lamina bonded to a receiver element, the lamina having a first surface and a second surface opposite the first, the thickness between the first surface and the second surface between about 1.5 microns and about 10 microns,

wherein the lamina is bonded to the receiver element at the first surface, with zero, one, or more layers intervening, and the second surface is exposed, and wherein the receiver element has a thickness of at least 80 microns; and

annealing the entire thickness of the bonded lamina with microwave energy,

wherein the lamina is suitable for use in the photovoltaic cell, and wherein the photovoltaic cell comprises the lamina.

2. The method of claim 1 further comprising the step of fabricating the photovoltaic cell.

3. The method of claim 1 wherein the semiconductor lamina is substantially crystalline.

4. The method of claim 1 wherein the receiver element comprises glass, metal, polymer, ceramic, or semiconductor material.

5. The method of claim 4 wherein the receiver element comprises glass.

6. The method of claim 1 wherein a metal layer is disposed between the lamina and the receiver element.

7. The method of claim 6 wherein, during the annealing step, microwave energy enters the lamina at the second surface and is reflected from the metal layer.

8. The method of claim 6 wherein a transparent conductive oxide layer is disposed between the lamina and the metal layer.

9. The method of claim 1 wherein, during the annealing step, microwave energy enters the lamina at the second surface and is absorbed at a depth of at least 2 microns beneath the second surface.

10. The method of claim 1 wherein, during the annealing step, microwave energy enters the lamina at the second surface and is absorbed at a depth of at least 4 microns beneath the second surface.

11. The method of claim 1 wherein the power of the microwave energy during the anneal step is between about 500 watts and about 5000 watts.

12. The method of claim 1 wherein, before the annealing step, the lamina is substantially monocrystalline silicon.

13. The method of claim 1 wherein, before the annealing step, the lamina includes an amorphous silicon, nanocrystalline, or microcrystalline silicon layer.

14. A method to form a photovoltaic cell, the method comprising the steps of:

defining a cleave plane in a substantially crystalline semiconductor donor wafer;

bonding the donor wafer at a first surface to a receiver element;

cleaving a substantially crystalline semiconductor lamina from the donor wafer at the cleave plane, wherein the lamina remains bonded to the receiver element at the first surface and a second surface of the lamina is created by cleaving, the second surface opposite the first, and wherein the lamina has a thickness of at least 2 microns; and

annealing the entire thickness of the bonded lamina with microwave energy to repair crystalline defects,

wherein the lamina is suitable for use in the photovoltaic cell, the photovoltaic cell comprising the lamina.

15. The method of claim 14 further comprising fabricating the photovoltaic cell.

16. The method of claim 14 wherein the receiver element comprises glass, metal, polymer, ceramic, or semiconductor material.

17. The method of claim 16 wherein the receiver element comprises glass.

18. The method of claim 14 wherein a metal layer is disposed between the lamina and the receiver element.

19. The method of claim 18 wherein, during the annealing step, microwave energy enters the lamina at the second surface and is reflected from the metal layer.

20. The method of claim 18 wherein a transparent conductive oxide is disposed between the lamina and the metal layer.

21. The method of claim 14 wherein the donor wafer is monocrystalline silicon.

22. The method of claim 14 wherein, during the bonding step, zero, one, or more layers are disposed between the donor wafer and the receiver element.

23. The method of claim 14 further comprising, before the annealing step, etching at the second surface to remove exfoliation damage.